- Email: [email protected]
Comparative leaf anatomical studies of someMallotusLour. (Euphorbiaceae) species
Botanical Journal of the Linnean Society (1996), 122: 137–153. With 11 figures
Comparative leaf anatomical studies of some Mallotus Lour. (Euphorbiaceae) species KHATIJAH HAJI HUSSIN, BKHTIAR ABDUL WAHAB AND CHE PIAH TEH Jabatan Botani, Fakulti Sains Hayat, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor Received June 1995, accepted for publication April 1996
A comparative study was undertaken on the leaves and petioles of 16 species of Mallotus in order to investigate anatomical variations of potential in species identification. There is a range of characters which varies between species. These include the outline of the midrib and petiole in transverse sections, the shape of the vascular tissue in midribs, the presence of central bundles in the petiole, the presence of terminal sclereids, enlarged tracheids, presence or absence of non-glandular trichomes, and parenchymatous sheaths in vascular bundles. A combination of these characters may be used to identify species. Anatomical data support the placing of only a few species into the respective sections. ©1996 The Linnean Society of London
ADDITIONAL KEY WORDS: — crystals – petiole – terminal sclereids – trichome. CONTENTS Introduction . . . . . . . . . Material and methods . . . . . . Results . . . . . . . . . . . Generic anatomical descriptions . Anatomical descriptions of species Discussion . . . . . . . . . . Significant anatomical features . . . Acknowledgements . . . . . . . References . . . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
137 138 139 139 141 151 151 153 153
INTRODUCTION
There are 28 species of Mallotus (Euphorbiaceae, tribe Acalypheae) recorded for peninsular Malaya and they are mainly distributed in the primary lowland forest. Some species extend up to Burma and Indo-China in the north, some as far as China and India. To the south, a few species extend to Sumatra and Java while some, such as M. repandus and M. tiliifolius, reach as far as New Caledonia and Fiji, respectively (Whitmore, 1973). Out of the 28 species recorded, two species, M. penangensis and M. griffithianus are endemic to Malaya, three are uncommon, four are rare and one, M. smilaciformis seems to have disappeared (Whitmore, 1973). Leaf morphological characters have been used for the identification of species (Ridley, 1924; Corner, 1952; Whitmore, 1973). Ridley (1924) divided the genus into 0024–4074/96/010137 + 17 $25.00/0
137
©1996 The Linnean Society of London
138
K. H. HUSSIN ET AL
TABLE 1. Sections in Mallotus with taxa included in this study Airy Shaw (1973)
Ridley (1924)
S. Hancea M. miquelianus M. griffithianus M. penangensis
S. Diplochlamys M. subpeltatus M. griffithianus S. Axenfeldia M. penangensis M. kingii
S. Mallotus M. paniculatus M. macrostachyus
S. Echinus M. barbatus M. macrostachyus
S. Polyadenii M. leucodermis M. muticus
S. Philippensis M. lecucodermis M. repands M. philippensis
S. Rottlera M. philippensis S. Rottleropsis M. tiliifolius M. dispar
S. Echinocroton M. tiliifolius M. dispar
S. Stylanthus M. oblongifolius
six sections based primarily on leaf morphology, while Airy Shaw (1973) divided the genus into eight sections also using leaf morphological characteristics (Table 1). Mallotus is often confused with Macaranga, a closely-related species. Corner (1952) differentiated Macaranga from Mallotus due to the presence of its red latex and its memercophytic habit, characters which are not available in herbarium specimens. Leaf anatomy is useful in systematic studies such as in the genus Euphorbia where leaf anatomical evidence supports the division of the genus into sub-genera or even genera (Sehgal & Paliwal, 1974). Apart from a brief mention of the anatomy of Mallotus by Metcalfe & Chalk (1950) no other work has been carried out on the systematic anatomy of the genus. This paper presents the results of a comparative study of the anatomy of leaves and petioles of 15 Mallotus species from peninsular Malaya and one from Thailand in order to investigate the potential of anatomical characters in species identification as well as to test the validity of the classification of the genus into sections. This systematic study of Mallotus is also undertaken as a contribution to the revision of the anatomy of the dicotyledons.
MATERIAL AND METHODS
Mallotus barbatus M¨uell. Arg. KELANTAN: Kg. Krian, 1986, A. Latiff, A. Zainuddin, Razali Jaman, Sani Miran, ALM 1598 (UKMB). KEDAH: Lunas, 1986, Hamid Salleh HS 2005 (UKMB). Mallotus dispar M¨uell. Arg. Thailand 1986, J.F. Maxwell. Mallotus griffithianus Hook. fil. PAHANG: 1975, Razali Jaman (UKMB). Mallotus kingii Hook. f. KELANTAN: 1987, Zainuddin, Sani & Buruk (UKMB). Mallotus leucodermis Hook. f. SELANGOR: Langat, 1975, A. Rahim (UKMB).
LEAF ANATOMY OF MALLOTUS
139
Mallotus macrostachyus (Miq.) M¨uell. Arg. KEDAH: Jalan Sungai Petani, 1986, Hamid Salleh HS 2015 (UKMB). SELANGOR: Jalan Rawang, 1986, Hamid Salleh HS 2015 (UKMB); Rumah Hijau UKM, 6.8.86 (UKMB). SABAH: 1984, A. Latiff Mohd. (UKMB). Mallotus miquelianus (Scheff.) Boerl. KEDAH: 1984, A. Zainuddin (UKMB). Mallotus muticus (M¨uell. Arg.) Airy Shaw. PAHANG: 1989, Airy Shaw (UKMB). Mallotus oblongifolius (Miq.) M¨uell. Arg. NEGRI SEMBILAN: 1981, A. Hamid (UKMB). Mallotus paniculatus (Lam.) M¨uell. Arg. JOHOR: Segamat, Jalan Muar, 4.8.86, (UKMB). KEDAH: 1975, A. Rahim Othman (UKMB). NEGRI SEMBILAN: Jeram Toi, 13.4.86 (UKMB). PAHANG: Genting Highland, 6.8.86 (UKMB). WILAYAH PERSEKUTUAN: Taman Templer, 2.8.86 (UKMB). Mallotus peltatus (Gessel) M¨uell. Arg. KEDAH: 1922, A. Zainuddin (UKMB). Mallotus penangensis M¨uell. Arg. PAHANG: 1985; A. Latiff Mohammad (UKMB). Mallotus philippensis (Lam.) M¨uell. Arg. JOHOR: 1990, RH 70 (UKMB). KEDAH: Permatang Tengah, 1986, Hamid Salleh HS 2006 (UKMB). NEGRI SEMBILAN: Hutan Simpan Serting, 1986, Hamid Salleh HS 2001 (UKMB). Mallotus repandus (Willd.) M¨uell. Arg. SABAH: 1987, Norhazni Mat Sani, NMS 0050 (UKMB). Mallotus subpeltatus M¨uell. Arg. SELANGOR: Klang, 1977, M. Kassim & Rahim (UKMB). Mallotus tiliifolius M¨uell. Arg. KEDAH: Langkawi, 1980, A. Latiff Mohammad, (UKMB). Specimens were collected in the field (voucher specimens deposited in Universiti Kebangsaan herbarium, UKMB) or studied from herbarium specimens. Specimens were fixed in FAA, sectioned on the sliding microtome and stained in safranin and alcian green. Sections were made from the middle part of the petioles and midribs. Herbarium specimens were boiled gently before fixation. Epidermal peels were prepared by treatment with Jeffrey’s fluid (10% nitric acid and 10% chromic acid, 1:1) and stained in alcian green. Leaf clearings were prepared by treating the specimens with 1% basic fuchsin in 10% KOH at 60°C. The cleaned specimens were washed in 50% alcohol then transferred to 70% alcohol and acidified with HCL. All slides were mounted in Euparal after dehydration. Only one leaf was sectioned from each specimen.
RESULTS
Generic anatomical descriptions Leaf surface EPIDERMAL CELLS:
adaxial and abaxial cells with wavy to sinuous walls. STOMATA: paracytic. TRICHOMES: glandular hairs present on abaxial surface of leaves of all species (Figs 1 & 3); simple, armed or stellate present in some. Lamina TS
EPIDERMAL CELLS:
adaxial and abaxial cells vary from as high as wide to three times wider than high. HYPODERMIS: not seen. CHLORENCHYMA: palisade cells in one layer in all species except M. paniculatus which has one to two layers, making up one third to just under half of leaf thickness, spongy cells in 2–8 layers. VASCULAR BUNDLES: collateral bundles with phloem and tracheary elements not arranged in any particular orientation; all species except M. barbatus with fibrous sheaths, with or without girders extending to adaxial epidermis. Vein endings dendroid (from cleared
140
K. H. HUSSIN ET AL
Figures 1–8. Mallotus. 1. Surface view of abaxial epidermis of M. tiliifolius: glandular trichome. 2. T.S. of M. penangensis lamina: terminal sclereid. 3. T.S. of M. dispar lamina: glandular trichome. 4. T.S. of M. kingii lamina: terminal sclereids under polarized light. 5. T.S. of M. leucodermis lamina: peltate-like trichome situated in papilla-lined crypt. 6. T.S. of M. griffithianus petiole: brachysclereids in ground tissue. 7. Abaxial epidermis of M. leucodermis: surface view of trichomes of Fig. 5. 8. T.S. of M. philippensis lamina: dense trichomes in crypts in abaxial epidermis. Scale bar = 50 µm in Figs 3 and 5, 80 µm in Figs 1, 2, 4, 6–8.
LEAF ANATOMY OF MALLOTUS
141
Figure 9. Cleared leaf of M. subpeltatus: terminal sclereids under polarized light. Scale bar = 30µm.
leaves), some with swollen tracheids or with terminal sclereids (Figs 2, 4 & 9). CRYSTALS: druses and/or solitary crystals present in idioblasts and sometimes scattered in palisade and spongy cells. Midrib TS U-shaped to semi-circular abaxially, adaxial side flat, convex or with ridges. COLLENCHYMA: not seen. Vascular tissue in an interrupted ring, some species with central bundles. BUNDLE SHEATHS: sclerenchymatous; strands of fibres incompletely encircling midrib complex. CRYSTALS: druses in phloem and parenchyma, solitary crystals infrequent (Fig. 10). Petiole TS OUTLINE: circular. EPIDERMIS: cells twice as high as wide to twice as wide as high. TRICHOMES: simple, armed or stellate. OUTER TISSUES: collenchyma absent; parenchyma in 5-13 layers. VASCULAR TISSUES: closed ring with 1–14 central bundles, uninterrupted except in M. miquelianus, M. dispar, M. peltatus, M. paniculatus, and M. philippensis. BUNDLE SHEATH: sclerenchymatous; strands of fibres usually incompletely encircling main vascular system except in M. penangensis and M. subpeltatus where the sheath is complete (Fig. 11). CENTRAL TISSUES: parenchymatous. CRYSTALS: druses in parenchyma and phloem, solitary crystals infrequent. Anatomical descriptions of species Leaf morphological and anatomical descriptions for species are listed in Tables 2–5. Other characters are as follows: Mallotus babatus. M¨uell. Arg. vascular bundles not surrounded by any sheaths; parenchymatous girders sometimes with fibres extending to adaxial epidermis; vein endings with swollen tracheids. Adaxial surface raised over vascular bundles. MIDRIB TS: semi-circular abaxially, adaxial side with ridge; vascular tissue with three small bundles and strands of phloem in centre region (Fig. 10J). LAMINA TS:
142
K. H. HUSSIN ET AL
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
parenchyma sclerenchyma xylem phloem
Figure 10. Transverse sections of midribs of Mallotus species. A, M. tiliifolius. B, M. dispar. C, M. miquelianus. D, M. paniculatus. E, M. peltatus. F, M. oblongifolius. G, M. repandus. H, M. penangensis. I, M. macrostachyus. J, M. barbatus. K, M. kingii. L, M. griffithianus. M, M. muticus. N, M. leucodermis. O, M. subpeltatus. P, M. philippensis. Scale bar = 2.5 mm.
LEAF ANATOMY OF MALLOTUS
Figure 11. Transverse sections of petioles of Mallotus species. A, M. miquelianus. B, M. tiliifolius. C, M. dispar. D, M. paniculatus. E, M. peltatus. F, M. oblongifolius. G, M. repandus. H, M. penangensis. I, M. macrostachyus. J, M. barbatus. K, M. kingii. I, M. griffithianus. M, M. muticus. N, M. leucodermis. O, M. philippensis. P, M. subpeltatus. Scale bar = 500 µm
143
Length (cm) 2.5–7.5 6.0–20.0 25.0–30.0 17.0–22.0
Shape
peltate, three-lobed
ovate to elliptic
minutely peltate, oblong
elliptic to oblong
M. barbatus
M. dispar
M. griffithianus
M. kingii 10.0–22.0 9.0–28.0 10.0–30.0 8.0–18.0 10.0–26.0 8.0–18.0 9.0–20.0 3.5–10.0
elliptic
ovate or rhomboid
ovate
obovate, minutely peltate
oblong to elliptic
trilobus & bilobus rhombic-ovate
peltate
oblong-lanceolate
M. miquelianus
M. muticus
M. oblongifolius
M. paniculatus
M. penangensis
M. philippensis
8.0–20.0 3.5–15.0
18.0–24.5
7.5–24.5
elliptical to ovate
rhombic-ovate
minutely peltate, oblong, spirally arranged
orbicular or tiangular-ovate
M. repandus
M. subpeltatus
M. tiliifolius
M. peltatus
M. leucodermis
M. macrostachyus
Species
5.5–15.5
6.5–10.0
1.5–6.0
4.0–15.0
1.0–3.5
3.0–11.0
4.0–13.0
4.0–8.0
4.0–8.5
4.5–8.0
7.0–13.0
5.5–8.5
5.5–7.0
8.0–10.0
3.0–11.0
2.6–6.0
Width (cm)
acuminate
cuspidate
acuminate
undulate
dentate
rounded, truncate or cordate
serrate
dentate
undulate
dentate
smooth
greyish white, glabrous
smooth or dentate
velvety
lamina glabrous, hairs on midrib
glabrous
finely velvety
fine hairs lamina glabrous, hairs on midbrib
brownish white, powdery
lamina glabrous, hairs on veins
velvety
hairy
1.5–7.5
5.5–7.5
0.5–5.5
2.5–8.0
0.8–2.0
2.5–12.0
2.5–13.0
1.2–8.0
1.0–5.5
2.0–7.0
2.5–25.0
2.5–7.5
1.0–3.5 glabrous
5.5–8.0
velvety on midrib & secondary veins
1.5–7.0
5.0–25.0
Length (cm)
Petiole
lamina glabrous, hairs on midrib
entire
dentate
smooth to wavy
undulate
entire
rounded
cuneate
acute roundish to cuneate
acute to acuminate
slightly cordate
cuneate
cuneate
cuneate
roundish
cuneate
rounded
cuneate
entire
slightly dentate
roundish to cuneate softly hairy
thickly hairy
smooth to slightly dentate
roundish
cuneate to rounded
Underside
Margin
Base
acuminate
acuminate
acute or acuminate
acuminate
cuspidate
acuminate
acute
acuminate
acuminate
cuspidate
acute
acute
Apex
Leaf
TABLE 2. Morphological characters of some Mallotus Lour. (Euphorbiaceae) species 144 K. H. HUSSIN ET AL
LEAF ANATOMY OF MALLOTUS
145
TABLE 3. Anatomical characters of some Mallotus Lour. (Euphorbiaceae) species Leaf thickness (mm) Species M. barbatus M. dispar M. griffithianus M. kingii M. leucodermis M. macrostachyus M. miquelianus M. muticus M. oblongifolius M. paniculatus M. peltatus M. penangensis M. philippensis M. repandus M. subpeltatus M. tiliifolius
Epidermal cell wall
Midrib
Lamina
Adaxial
Abaxial
1.62 0.63 0.87 1.11 0.70 0.92 0.60 0.71 0.93 0.63 0.92 0.60 0.73 0.67 0.71 1.08
0.10 0.10 0.24 0.11 0.20 0.10 0.11 0.11 0.12 0.10 0.11 0.16 0.11 0.11 0.10 0.08
sinuous sinuous sinuous sinuous wavy–slightly sinuous sinuous sinuous sinuous sinuous wavy–straight sinuous sinuous sinuous wavy–slightly sinuous sinuous sinuous
wavy–straight sinuous sinuous sinuous sinuous sinuous sinuous wavy wavy wavy wavy–sinuous sinuous not observed wavy–slightly sinuous sinuous wavy
Mallotus dispar M¨uell. Arg. MIDRIB TS: U-shaped abaxially, adaxial surface nearly flat; thick-walled cells present below adaxial and abaxial epidermis. Vascular tissue with smaller bundles situated laterally to adaxial side of main system (Fig. 10B). Mallotus griffithianus Hook. fil. semi-circular abaxially, adaxial side flat (Fig. 10L). Adaxial surface raised over larger vascular bundles. PETIOLE TS: brachysclereids present in ground tissue (Fig. 6). MIDRIB TS:
Mallotus kingii Hook. f. LAMINA TS: vein endings sometimes with slightly enlarged tracheids. MIDRIB TS: semicircular abaxially, adaxial surface with low broad ridge; vascular tissue with a small central bundle (Fig. 10K). Mallotus leucodermis Hook. f. peltate trichomes in papilla-lined crypts (Fig. 5). MIDRIB TS: U-shaped abaxially, adaxial side slightly ridged; vascular tissue with no central bundles (Fig. 10N).
LAMINA TS:
Mallotus macrostachyus (Miq.) M¨uell. Arg. TS: adaxial epidermal cells conical in shape. Lamina bundles with parenchymatous girders to adaxial epidermis; vein endings with slightly swollen tracheids. Adaxial surface raised over larger vascular bundles. MIDRIB TS: U-shaped abaxially, adaxial side nearly flat with slight ridge; vascular tissue with one central bundle (Fig. 10I). Inner ground tissue with secretory cells.
LAMINA
Mallotus miquelianus (Scheff.) Boerl. adaxial surface bulging over large veins. MIDRIB TS: U-shaped abaxially,
LAMINA TS:
as high as wide to 3 times wider than high as high as wide to twice as wide as high 2–5 times wider than high 2–3 times wider than high as high as wide to 4 times wider than high 3–4 times wider than high 3–4 times wider than high as high as wide to twice as wide as high 1–4 times wider than high as high as wide to twice as wide as high 2–3 times wider than high
simple, multicellular with arms & stellate
—
—
peltate in papillalined crypts
stellate
simple, multicellular with arms & stellate
—
simple, multicellular with 2–3 arms
stalked stellate
simple, multicellular with arms
—
M. dispar
M. griffithianus
M. kingii
M. macrostachyus
M. miquelianus
M. oblongifolius
M. paniculatus
M. penangensis
M. peltatus
M. muticus
M. leucodermis
3–5 times wider than high
stalked stellate
M. barbatus
Adaxial
Species
twice as wide as high
as high as wide to twice as high as wide
twice as wide as high
2–3 times wider than high
3–4 times wider than high
2–3 times wider than high
2–3 times wider than high
2–3 times wider than high
2–3 times wider than high
2–3 times wider than high
once to twice as wide as high
3–5 times wider than high
Abaxial
Epidermal cell (size)
Trichomes (non-glandular)
just under half of leaf thickness
just under half of leaf thickness
outer layer just under half of leaf thickness
just under half of leaf thickness
just under quarter of leaf thickness
just under half of leaf thickness
just under half of leaf thickness
1/3 of leaf thickness
just under half of leaf thickness
just under half of leaf thickness
just under half of leaf thickness
more than half of leaf thickness
Palisade thickness
Lamina
5–6
4–6
1–2
4–5
6–7
3–4
2
7–10
4–5
5–6
3–4
2
Mesophyll (layers)
TABLE 4. Anatomical characters of some Mallotus Lour. (Euphorbiaceae) species
++
++
–
++
+
+
–
+
++
+++
–
+
Terminal sclereids
palisade, mesophyll
palisade mesophyll
mesophyll
in idioblasts
in idioblasts
*palisade
mesophyll
palisade infrequent
—
—
palisade, mesophyll
mesophyll
Druses
–
+
+
+
+
+
+
+
+
–
+
+
Idioblasts
146 K. H. HUSSIN ET AL
as high as wide to twice as wide as high 2–3 times wider than high as high as wide to twice as wide as high as high as wide to 3 times wider than high
simple, stellate in crypts
simple, unicellular and short
simple, unicellular and short
simple, multicellular with arms & stellate
M. philippensis
M. repandus
M. subpeltatus
as high as wide to twice as wide as high
2–3 times wider than high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
Abaxial
just under half of leaf thickness
just under half of leaf thickness
just under half of leaf thickness
1/3 of leaf thickness
Palisade thickness
3–4
4–5
3
2–8
Mesophyll (layers)
+
++
–
+
Terminal sclereids
palisade, mesophyll
palisade
in idioblasts
mesophyll
Druses
Terminal sclereids: + = infrequent, ++ = present, +++ = abundant; *Druses = both druse and solitary crystals present; Idioblasts: + = present, -ve = absent.
M. tilifolius
Species
Adaxial
Epidermal cell (size)
Trichomes (non-glandular)
Lamina
TABLE 4. continued
–
+
+
+
Idioblasts
LEAF ANATOMY OF MALLOTUS 147
phloem, parenchyma infrequent *phloem, *parenchyma —
phloem, *parenchyma phloem, parenchyma phloem, *parenchyma parenchyma, phloem infrequent phloem, solitary in parenchyma phloem, parenchyma phloem, solitary in parenchyma
stalked stellate
simple, armed & stellate
—
simple, infrequent
—
—
multicellular with arms
—
stalked stellate
simple, multicellular with arms and stellate
M. barbatus
M. dispar
M. griffithianus
M. leucodermis
M. macrostachyus
M. miquelianus
M. oblongifolius
M. paniculatus
M. peltatus
M. muticus
Druses
Trichomes
Species
Midrib
twice as wide as high
twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
twice as wide as high
as high as wide to twice as wide as high
Epidermal cell (size)
8–12
10
10–11
7–10
8–10
6–7
10–11
5–6
11–13
7–10
Outer parenchymatous tissue (layers)
2–3
6–9
1–3
1
1–2
6–11
13–16
1
1
13–16
Central bundles
Petiole
parenchyma
Druses
*parenchyma
phloem, parenchyma
*parenchyma infrequent
—
parenchyma
parenchyma
*parenchyma, phloem abundant
parenchyma infrequent
*parenchyma
TABLE 5. Anatomical characters of some Mallotus Lour. (Euphorbiaceae) species
simple & stellate
stellate
simple & stellate
simple unicellular, multicellular with arms
stellate
stalked stellate
—
simple, unicellular but infrequent
simple, multicellular with two-armed
stalked stellate
Trichomes
148 K. H. HUSSIN ET AL
*phloem, *parenchyma
*parenchyma, phloem parenchyma, phloem parenchyma, phloem parenchyma phloem
simple
simple, multicellular stellate
—
simple, multicellular with arms
—
M. penangensis
M. philippensis
M. repandus
M. subpeltatus
M. tiliifolius
*Druses = both druse and solitary crystals present
Druses
Trichomes
Species
Midrib
as high as wide to twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
one and a half times higher than wide to twice as wide as high
Epidermal cell (size)
TABLE 5. continued
11–13
8–9
6–7
8–10
7–8
Outer parenchymatous tisse (layers)
1
4
2
1
1
Central bundles
Petiole
parenchyma, phloem, solitary infrequent
parenchyma
parenchyma, phloem
phloem, *parenchyma
*parenchyma infrequent
Druses
simple, multicellular with two-armed
simple, unicellular, short, infrequent
simple, unicellular and short
simple unicellular, multicellular stellate
simple, unicellular
Trichomes LEAF ANATOMY OF MALLOTUS 149
150
K. H. HUSSIN ET AL
adaxial side nearly flat; vascular tissue consists of two main strands adaxially and abaxially with two small bundles situated laterally to main system (Fig. 10C). Mallotus muticus (M¨uell. Arg.) Airy Shaw MIDRIB TS: arc-shaped abaxially, adaxial side with sharp ridge; vascular tissue with no central bundles (Fig. 10M). Mallotus oblongifolius M¨uell. Arg. LAMINA TS: adaxial surface bulging over large bundles. MIDRIB TS: semi-circular abaxially, raised adaxially; strands of fibres present in adaxial ridge (Fig. 10F). Mallotus paniculatus (Lam.) M¨uell. Arg. LAMINA TS: vascular bundles with parenchymatous girders to adaxial epidermis; vein endings with swollen tracheids. Abaxial surface bulging over large vascular bundles. MIDRIB TS: U-shaped abaxially, adaxial side nearly flat; vascular tissue with one central bundle (Fig. 10D). Mallotus peltatus (Gessel.) M¨uell. Arg. abaxial surface bulge out over vascular bundles. MIDRIB TS: semi-circular abaxially, raised adaxially; vascular tissue in an interrupted ring (Fig. 10E).
LAMINA TS:
Mallotus penangensis M¨uell. Arg. vascular bundles with sclerenchymatous girders to adaxial epidermis. MIDRIB TS: semi-circular abaxially, adaxial side sharply raised; vascular tissue consisting of two main arcs, the larger one abaxially (Fig. 10H). PETIOLE TS: Glandular cells abundant in ground tissue, some with dark contents. LAMINA TS:
Mallotus philippensis (Lam.) M¨uell. Arg. LAMINA TS: trichomes in crypts (Fig. 8) in abaxial surface. Enlarged tracheids infrequent. Large vascular bundles with parenchymatous extension to adaxial epidermis. Adaxial surface raised over larger vascular bundles. MIDRIB TS: semicircular abaxially, adaxial side flat to slightly raised. Thick-walled parenchyma cells below adaxial epidermis and few layers to inside of abaxial epidermis. Vascular tissue with no central bundles (Fig. 10P). Mallotus repandus (Willd.) M¨uell. Arg. LAMINA TS: vein endings sometimes with enlarged tracheids, adaxial surface bulging over larger vascular bundles. MIDRIB TS: circular abaxially, raised adaxially; vascular tissue consisting of two main arcs with small lateral bundles, strands of fibres in ground tissue above vascular strand (Fig. 10G). Mallotus subpeltatus M¨uell. Arg. LAMINA TS: adaxial surface raised over larger vascular bundles. MIDRIB TS: U-shaped abaxially, adaxial side flat to slightly convex; vascular tissue with smaller bundles in centre region (Fig. 10 O). Mallotus tiliifolius M¨uell. Arg. LAMINA TS: abaxial surface bulging over vascular bundles.
MIDRIB TS:
U-shaped
LEAF ANATOMY OF MALLOTUS
151
abaxially, adaxial side flat; vascular tissue with smaller bundles situated laterally to adaxial side of main system (Fig. 10A).
DISCUSSION
Significant anatomical features Results of the study show that there is considerable anatomical variation between the 16 species of Mallotus studied. However, some characters are present in all of them. All have a single layer of palisade cells of variable height, except M. paniculatus which varies from one to two layers. A hypodermal layer was not seen in any of the species. Druses are present in enlarged cells (idioblasts) in the palisade layer of most species. In some species the druses are not only confined to the idioblasts but also occur in the palisade and spongy mesophyll cells. In the vascular tissue, druses are usually present in the parenchyma cells of the midrib of the leaves and petioles as well as in the phloem cells. In some species solitary crystals are also present. In all the specimens studied it was not possible to identify collenchyma cells in the midrib or petioles. In some species the cells are noticeably absent, but in others thickwalled parenchyma cells resembling collenchyma cells are present especially in herbarium specimens. Since these could probably be due to the shrinking effect of drying which was not reversed fully, their presence is reported as ‘not seen’. Another feature which was observed but needs confirmation is the presence of small cells to the inner side of the xylem tissue which are not lignified. In M. macrostachyus they occur in groups in the ground tissue in the middle of the midrib. These cells on close observation resemble phloem tissue but this needs verification. Paracytic stomata were observed for all the species except M. philippensis where the presence of persistent trichomes made it impossible to observe the stomata. The ‘rubiaceous’ or paracytic type is characteristic for the tribe Acalypheae (Metcalfe & Chalk, 1950) and forms the basic type for the family (Raju & Rao, 1977), although the anomocytic type is more common in Euphorbia species (Kakkar & Paliwal, 1972). On the underside of the lamina all species have glandular trichomes (Figs 1 & 3). In addition, non-glandular trichomes are also present except in M. kingii, M. griffithianus, M. muticus and M. penangensis. M. leucodermis has only peltate trichomes which is a useful diagnostic character. According to Solereder (1908) glandular hairs are more frequent in the Acalyphae than elsewhere in the Euphorbiaceae. In M. philippensis the presence of trichome-lined crypts on the underside of leaves is a diagnostic character for the species. The vein endings of the vascular system in all the species are of the dendroid type with two species having veins ending with swollen tracheids. These are M. macrostachyus, M. repandus, M. barbatus and sometimes M. philippensis. Such tracheids have been observed in some genera of the Euphorbiaceae (Metcalfe & Chalk, 1950). In some species terminal sclereids are frequent to abundant. This may be similar to the ‘sclerenchymatous elements’ as reported by Metcalfe & Chalk (1950) for a few species of other genera in the family as well as to the ‘filiform’ sclereids observed in Dicoelia affinis and several Cleistanthus species of the Phyllanthoideae (Levin, 1986).
152
K. H. HUSSIN ET AL
According to Solereder (1908) “sclerenchymatous fibres running freely in the leaf are found chiefly in the tribe Acalypheae”. The presence of leaf sclereids may be useful in taxonomy. Their occurrence in Androstachys johnsonii (ex-Euphorbiaceae) supports the separation of the genus into the family Androstachydaceae (Alvin & Rao, 1987). The outer walls of the adaxial epidermal cells in the lamina of M. macrostachyus are conical in shape. This feature was not observed in the rest of the species and hence is diagnostic for M. macrostachyus. The vascular bundles in the lamina of M. paniculatus, M. macrostachyrus, M. barbatus and M. philippensis have parenchymatous extensions to the adaxial epidermis. In M. penangensis these extensions consist of sclerenchyma. This feature has been observed for a few Euphorbia species (Metcalfe & Chalk, 1950). For most of the species of Mallotus studied except M. leucodermis, M. kingii, M. muticus and M. penangensis the adaxial surface bulges out over the larger vascular bundles. Transverse sections of midribs reveal variations in the shape of the adaxial and abaxial surfaces. The adaxial surface varies from flat to slightly concave, convex and ridged. The ridge is very prominent in M. peltatus, M. oblongifolius, M. repandus, M. penangensis and M. muticus while in M. macrostachyus and M. barbatus this ridge is much lower. The abaxial surface shows slight variations, which when combined together with the adaxial surface, may be diagnostic for certain species such as M. muticus. The vascular tissue of the midrib is of the interrupted ‘O’ type. Transverse sections of midribs show some variations between species (Fig. 10). In some species central bundles are present as in M. paniculatus, M. barbatus, M. kingii and M. macrostachyus while in M. tiliifolius, M. dispar and M. subpeltatus the adaxial strand of the vascular tissue is broken into several bundles. The structure of the midrib in transverse section is therefore a useful character in the systematic anatomy of the genus. The general vascular system in the petiole is of the ‘O’ type vascular strand. However, while central bundles are present in the midrib of certain species only, they are present in the petioles of all species but the number varies between species (Fig. 11). M. miquelianus, M. tiliifolius, M. dispar, M. penangensis, M. kingii, M. griffithianus, M. muticus, M. leucodermis and M. philippensis, have one large central bundle. In M. peltatus, M. oblongifolius, M. repandus and M. subpeltatus there are two to four small bundles while in M. paniculatus, M. macrostachyus and M. barbatus the number ranges from six to sixteen. In species with more than one central bundle the number of these bundles varies between specimens. The range in number rather than the exact figure is more useful taxonomically. In M. graffithianus there are brachysclereids present in the parenchyma tissue and this can be a useful diagnostic character. Taxonomic implications of characters These anatomical characters in combination are very useful in the identification of Mallotus species. The results however do not show any clustering of characters which could be used to classify the genus into broad groups. With respect to sectional groupings as made by Ridley (1924) and Airy Shaw (1973), M. tiliifolius and M. dispar which are classified into the same section, S. Echinocroton (Ridley, 1924) and S. Rottleropsis (Airy Shaw, 1973) have nearly similar midrib structure in transverse sections. Both have only one central bundle in the petiole. Similarly, M. macrostachyus and M. barbatus which are both put in the Section Echinus by Ridley are quite similar in the midrib structure. Anatomical data in this case support the placing of those
LEAF ANATOMY OF MALLOTUS
153
species into the respective sections. In the other sections anatomical characters do not support the classification. According to Airy Shaw (1973) in his treatment of the Bornean species, M. griffithianus is related to M. kingii of peninsular Malaysia. Anatomically, they share some common characters such as the presence of terminal sclereids and a large central bundle in the petiole. Both have glandular trichomes only on the lamina. However transverse sections of the midrib show differences in the adaxial surface and the presence of a central bundle in M. kingii. This supports the placing of the two species into different sections by Ridley (1924). Results of this study also do not show any correlation of anatomical characters exclusively for M. muticus and M. leucodermis which according to Whitmore (1973) and Airy Shaw (1973) are very similar in all respects except in the character of the fruit.
ACKNOWLEDGEMENTS
The authors wish to thank Dr D.F. Cutler of Jodrell Laboratory, Kew Gardens for critical reading of the manuscript and Ahmed Zainudin Ibrahim, Hamid Salleh and Sukaimi Rasmi for their technical help. This work was partly supported by IRPA grant (4-07-03-007).
REFERENCES Airy Shaw HK. 1973. The Euphorbiaceae of Borneo. Kew Bull. Additional Services IV, London: HMSO. Alvin KL, Rao TA. 1987. On the unusual distribution pattern of leaf sclereids in Androstachys johnsonii Prain (Euphorbiaceae). Botanical Journal of the Linnean Society 95: 55–60. Corner EJH. 1952. Wayside Trees of Malaya. 2nd edn. Vol 1. Singapore: Government Printer. Kakkar L, Paliwal GS. 1972. Studies on the leaf anatomy of Euphorbia V. Epidermis. Proceedings of the Indian National Science Academy, B 40: 55–67. Levin GA. 1986. Systematic foliar morphology of Phyllanthoideae (Euphorbiaceae). I. Conspectus. Annals of the Missouri Botanical Gardens 73: 29–85. Metcalfe CR, Chalk L. 1950. Anatomy of the Dicotyledons. Vol 1. Oxford: Clarendon Press. Raju VS, Rao PN. 1977. Variation in the structure and development of foliar stomata in the Euphorbiaceae. Botanical Journal of the Linnean Society 75: 69–97. Ridley HN 1924. Flora of the Malay Peninsula. Vol. III. London: L. Reeve & Co. Sehgal L, Paliwal GS. 1974. Studies on the leaf anatomy of Euphorbia VII. General conclusions and systematic considerations. Phytomorphology 24: 141–151. Solereder H. 1908. Systematic Anatomy of the Dicotyledons. Transl. L.A. Boodle & F.E. Fritsch. Oxford: Clarendon Press. Whitmore TC. 1973. Tree Flora of Malaya, A Manual for Foresters, vol 2. Kuala Lumpur: Longman.
Comparative leaf anatomical studies of some Mallotus Lour. (Euphorbiaceae) species KHATIJAH HAJI HUSSIN, BKHTIAR ABDUL WAHAB AND CHE PIAH TEH Jabatan Botani, Fakulti Sains Hayat, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor Received June 1995, accepted for publication April 1996
A comparative study was undertaken on the leaves and petioles of 16 species of Mallotus in order to investigate anatomical variations of potential in species identification. There is a range of characters which varies between species. These include the outline of the midrib and petiole in transverse sections, the shape of the vascular tissue in midribs, the presence of central bundles in the petiole, the presence of terminal sclereids, enlarged tracheids, presence or absence of non-glandular trichomes, and parenchymatous sheaths in vascular bundles. A combination of these characters may be used to identify species. Anatomical data support the placing of only a few species into the respective sections. ©1996 The Linnean Society of London
ADDITIONAL KEY WORDS: — crystals – petiole – terminal sclereids – trichome. CONTENTS Introduction . . . . . . . . . Material and methods . . . . . . Results . . . . . . . . . . . Generic anatomical descriptions . Anatomical descriptions of species Discussion . . . . . . . . . . Significant anatomical features . . . Acknowledgements . . . . . . . References . . . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . . .
137 138 139 139 141 151 151 153 153
INTRODUCTION
There are 28 species of Mallotus (Euphorbiaceae, tribe Acalypheae) recorded for peninsular Malaya and they are mainly distributed in the primary lowland forest. Some species extend up to Burma and Indo-China in the north, some as far as China and India. To the south, a few species extend to Sumatra and Java while some, such as M. repandus and M. tiliifolius, reach as far as New Caledonia and Fiji, respectively (Whitmore, 1973). Out of the 28 species recorded, two species, M. penangensis and M. griffithianus are endemic to Malaya, three are uncommon, four are rare and one, M. smilaciformis seems to have disappeared (Whitmore, 1973). Leaf morphological characters have been used for the identification of species (Ridley, 1924; Corner, 1952; Whitmore, 1973). Ridley (1924) divided the genus into 0024–4074/96/010137 + 17 $25.00/0
137
©1996 The Linnean Society of London
138
K. H. HUSSIN ET AL
TABLE 1. Sections in Mallotus with taxa included in this study Airy Shaw (1973)
Ridley (1924)
S. Hancea M. miquelianus M. griffithianus M. penangensis
S. Diplochlamys M. subpeltatus M. griffithianus S. Axenfeldia M. penangensis M. kingii
S. Mallotus M. paniculatus M. macrostachyus
S. Echinus M. barbatus M. macrostachyus
S. Polyadenii M. leucodermis M. muticus
S. Philippensis M. lecucodermis M. repands M. philippensis
S. Rottlera M. philippensis S. Rottleropsis M. tiliifolius M. dispar
S. Echinocroton M. tiliifolius M. dispar
S. Stylanthus M. oblongifolius
six sections based primarily on leaf morphology, while Airy Shaw (1973) divided the genus into eight sections also using leaf morphological characteristics (Table 1). Mallotus is often confused with Macaranga, a closely-related species. Corner (1952) differentiated Macaranga from Mallotus due to the presence of its red latex and its memercophytic habit, characters which are not available in herbarium specimens. Leaf anatomy is useful in systematic studies such as in the genus Euphorbia where leaf anatomical evidence supports the division of the genus into sub-genera or even genera (Sehgal & Paliwal, 1974). Apart from a brief mention of the anatomy of Mallotus by Metcalfe & Chalk (1950) no other work has been carried out on the systematic anatomy of the genus. This paper presents the results of a comparative study of the anatomy of leaves and petioles of 15 Mallotus species from peninsular Malaya and one from Thailand in order to investigate the potential of anatomical characters in species identification as well as to test the validity of the classification of the genus into sections. This systematic study of Mallotus is also undertaken as a contribution to the revision of the anatomy of the dicotyledons.
MATERIAL AND METHODS
Mallotus barbatus M¨uell. Arg. KELANTAN: Kg. Krian, 1986, A. Latiff, A. Zainuddin, Razali Jaman, Sani Miran, ALM 1598 (UKMB). KEDAH: Lunas, 1986, Hamid Salleh HS 2005 (UKMB). Mallotus dispar M¨uell. Arg. Thailand 1986, J.F. Maxwell. Mallotus griffithianus Hook. fil. PAHANG: 1975, Razali Jaman (UKMB). Mallotus kingii Hook. f. KELANTAN: 1987, Zainuddin, Sani & Buruk (UKMB). Mallotus leucodermis Hook. f. SELANGOR: Langat, 1975, A. Rahim (UKMB).
LEAF ANATOMY OF MALLOTUS
139
Mallotus macrostachyus (Miq.) M¨uell. Arg. KEDAH: Jalan Sungai Petani, 1986, Hamid Salleh HS 2015 (UKMB). SELANGOR: Jalan Rawang, 1986, Hamid Salleh HS 2015 (UKMB); Rumah Hijau UKM, 6.8.86 (UKMB). SABAH: 1984, A. Latiff Mohd. (UKMB). Mallotus miquelianus (Scheff.) Boerl. KEDAH: 1984, A. Zainuddin (UKMB). Mallotus muticus (M¨uell. Arg.) Airy Shaw. PAHANG: 1989, Airy Shaw (UKMB). Mallotus oblongifolius (Miq.) M¨uell. Arg. NEGRI SEMBILAN: 1981, A. Hamid (UKMB). Mallotus paniculatus (Lam.) M¨uell. Arg. JOHOR: Segamat, Jalan Muar, 4.8.86, (UKMB). KEDAH: 1975, A. Rahim Othman (UKMB). NEGRI SEMBILAN: Jeram Toi, 13.4.86 (UKMB). PAHANG: Genting Highland, 6.8.86 (UKMB). WILAYAH PERSEKUTUAN: Taman Templer, 2.8.86 (UKMB). Mallotus peltatus (Gessel) M¨uell. Arg. KEDAH: 1922, A. Zainuddin (UKMB). Mallotus penangensis M¨uell. Arg. PAHANG: 1985; A. Latiff Mohammad (UKMB). Mallotus philippensis (Lam.) M¨uell. Arg. JOHOR: 1990, RH 70 (UKMB). KEDAH: Permatang Tengah, 1986, Hamid Salleh HS 2006 (UKMB). NEGRI SEMBILAN: Hutan Simpan Serting, 1986, Hamid Salleh HS 2001 (UKMB). Mallotus repandus (Willd.) M¨uell. Arg. SABAH: 1987, Norhazni Mat Sani, NMS 0050 (UKMB). Mallotus subpeltatus M¨uell. Arg. SELANGOR: Klang, 1977, M. Kassim & Rahim (UKMB). Mallotus tiliifolius M¨uell. Arg. KEDAH: Langkawi, 1980, A. Latiff Mohammad, (UKMB). Specimens were collected in the field (voucher specimens deposited in Universiti Kebangsaan herbarium, UKMB) or studied from herbarium specimens. Specimens were fixed in FAA, sectioned on the sliding microtome and stained in safranin and alcian green. Sections were made from the middle part of the petioles and midribs. Herbarium specimens were boiled gently before fixation. Epidermal peels were prepared by treatment with Jeffrey’s fluid (10% nitric acid and 10% chromic acid, 1:1) and stained in alcian green. Leaf clearings were prepared by treating the specimens with 1% basic fuchsin in 10% KOH at 60°C. The cleaned specimens were washed in 50% alcohol then transferred to 70% alcohol and acidified with HCL. All slides were mounted in Euparal after dehydration. Only one leaf was sectioned from each specimen.
RESULTS
Generic anatomical descriptions Leaf surface EPIDERMAL CELLS:
adaxial and abaxial cells with wavy to sinuous walls. STOMATA: paracytic. TRICHOMES: glandular hairs present on abaxial surface of leaves of all species (Figs 1 & 3); simple, armed or stellate present in some. Lamina TS
EPIDERMAL CELLS:
adaxial and abaxial cells vary from as high as wide to three times wider than high. HYPODERMIS: not seen. CHLORENCHYMA: palisade cells in one layer in all species except M. paniculatus which has one to two layers, making up one third to just under half of leaf thickness, spongy cells in 2–8 layers. VASCULAR BUNDLES: collateral bundles with phloem and tracheary elements not arranged in any particular orientation; all species except M. barbatus with fibrous sheaths, with or without girders extending to adaxial epidermis. Vein endings dendroid (from cleared
140
K. H. HUSSIN ET AL
Figures 1–8. Mallotus. 1. Surface view of abaxial epidermis of M. tiliifolius: glandular trichome. 2. T.S. of M. penangensis lamina: terminal sclereid. 3. T.S. of M. dispar lamina: glandular trichome. 4. T.S. of M. kingii lamina: terminal sclereids under polarized light. 5. T.S. of M. leucodermis lamina: peltate-like trichome situated in papilla-lined crypt. 6. T.S. of M. griffithianus petiole: brachysclereids in ground tissue. 7. Abaxial epidermis of M. leucodermis: surface view of trichomes of Fig. 5. 8. T.S. of M. philippensis lamina: dense trichomes in crypts in abaxial epidermis. Scale bar = 50 µm in Figs 3 and 5, 80 µm in Figs 1, 2, 4, 6–8.
LEAF ANATOMY OF MALLOTUS
141
Figure 9. Cleared leaf of M. subpeltatus: terminal sclereids under polarized light. Scale bar = 30µm.
leaves), some with swollen tracheids or with terminal sclereids (Figs 2, 4 & 9). CRYSTALS: druses and/or solitary crystals present in idioblasts and sometimes scattered in palisade and spongy cells. Midrib TS U-shaped to semi-circular abaxially, adaxial side flat, convex or with ridges. COLLENCHYMA: not seen. Vascular tissue in an interrupted ring, some species with central bundles. BUNDLE SHEATHS: sclerenchymatous; strands of fibres incompletely encircling midrib complex. CRYSTALS: druses in phloem and parenchyma, solitary crystals infrequent (Fig. 10). Petiole TS OUTLINE: circular. EPIDERMIS: cells twice as high as wide to twice as wide as high. TRICHOMES: simple, armed or stellate. OUTER TISSUES: collenchyma absent; parenchyma in 5-13 layers. VASCULAR TISSUES: closed ring with 1–14 central bundles, uninterrupted except in M. miquelianus, M. dispar, M. peltatus, M. paniculatus, and M. philippensis. BUNDLE SHEATH: sclerenchymatous; strands of fibres usually incompletely encircling main vascular system except in M. penangensis and M. subpeltatus where the sheath is complete (Fig. 11). CENTRAL TISSUES: parenchymatous. CRYSTALS: druses in parenchyma and phloem, solitary crystals infrequent. Anatomical descriptions of species Leaf morphological and anatomical descriptions for species are listed in Tables 2–5. Other characters are as follows: Mallotus babatus. M¨uell. Arg. vascular bundles not surrounded by any sheaths; parenchymatous girders sometimes with fibres extending to adaxial epidermis; vein endings with swollen tracheids. Adaxial surface raised over vascular bundles. MIDRIB TS: semi-circular abaxially, adaxial side with ridge; vascular tissue with three small bundles and strands of phloem in centre region (Fig. 10J). LAMINA TS:
142
K. H. HUSSIN ET AL
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
parenchyma sclerenchyma xylem phloem
Figure 10. Transverse sections of midribs of Mallotus species. A, M. tiliifolius. B, M. dispar. C, M. miquelianus. D, M. paniculatus. E, M. peltatus. F, M. oblongifolius. G, M. repandus. H, M. penangensis. I, M. macrostachyus. J, M. barbatus. K, M. kingii. L, M. griffithianus. M, M. muticus. N, M. leucodermis. O, M. subpeltatus. P, M. philippensis. Scale bar = 2.5 mm.
LEAF ANATOMY OF MALLOTUS
Figure 11. Transverse sections of petioles of Mallotus species. A, M. miquelianus. B, M. tiliifolius. C, M. dispar. D, M. paniculatus. E, M. peltatus. F, M. oblongifolius. G, M. repandus. H, M. penangensis. I, M. macrostachyus. J, M. barbatus. K, M. kingii. I, M. griffithianus. M, M. muticus. N, M. leucodermis. O, M. philippensis. P, M. subpeltatus. Scale bar = 500 µm
143
Length (cm) 2.5–7.5 6.0–20.0 25.0–30.0 17.0–22.0
Shape
peltate, three-lobed
ovate to elliptic
minutely peltate, oblong
elliptic to oblong
M. barbatus
M. dispar
M. griffithianus
M. kingii 10.0–22.0 9.0–28.0 10.0–30.0 8.0–18.0 10.0–26.0 8.0–18.0 9.0–20.0 3.5–10.0
elliptic
ovate or rhomboid
ovate
obovate, minutely peltate
oblong to elliptic
trilobus & bilobus rhombic-ovate
peltate
oblong-lanceolate
M. miquelianus
M. muticus
M. oblongifolius
M. paniculatus
M. penangensis
M. philippensis
8.0–20.0 3.5–15.0
18.0–24.5
7.5–24.5
elliptical to ovate
rhombic-ovate
minutely peltate, oblong, spirally arranged
orbicular or tiangular-ovate
M. repandus
M. subpeltatus
M. tiliifolius
M. peltatus
M. leucodermis
M. macrostachyus
Species
5.5–15.5
6.5–10.0
1.5–6.0
4.0–15.0
1.0–3.5
3.0–11.0
4.0–13.0
4.0–8.0
4.0–8.5
4.5–8.0
7.0–13.0
5.5–8.5
5.5–7.0
8.0–10.0
3.0–11.0
2.6–6.0
Width (cm)
acuminate
cuspidate
acuminate
undulate
dentate
rounded, truncate or cordate
serrate
dentate
undulate
dentate
smooth
greyish white, glabrous
smooth or dentate
velvety
lamina glabrous, hairs on midrib
glabrous
finely velvety
fine hairs lamina glabrous, hairs on midbrib
brownish white, powdery
lamina glabrous, hairs on veins
velvety
hairy
1.5–7.5
5.5–7.5
0.5–5.5
2.5–8.0
0.8–2.0
2.5–12.0
2.5–13.0
1.2–8.0
1.0–5.5
2.0–7.0
2.5–25.0
2.5–7.5
1.0–3.5 glabrous
5.5–8.0
velvety on midrib & secondary veins
1.5–7.0
5.0–25.0
Length (cm)
Petiole
lamina glabrous, hairs on midrib
entire
dentate
smooth to wavy
undulate
entire
rounded
cuneate
acute roundish to cuneate
acute to acuminate
slightly cordate
cuneate
cuneate
cuneate
roundish
cuneate
rounded
cuneate
entire
slightly dentate
roundish to cuneate softly hairy
thickly hairy
smooth to slightly dentate
roundish
cuneate to rounded
Underside
Margin
Base
acuminate
acuminate
acute or acuminate
acuminate
cuspidate
acuminate
acute
acuminate
acuminate
cuspidate
acute
acute
Apex
Leaf
TABLE 2. Morphological characters of some Mallotus Lour. (Euphorbiaceae) species 144 K. H. HUSSIN ET AL
LEAF ANATOMY OF MALLOTUS
145
TABLE 3. Anatomical characters of some Mallotus Lour. (Euphorbiaceae) species Leaf thickness (mm) Species M. barbatus M. dispar M. griffithianus M. kingii M. leucodermis M. macrostachyus M. miquelianus M. muticus M. oblongifolius M. paniculatus M. peltatus M. penangensis M. philippensis M. repandus M. subpeltatus M. tiliifolius
Epidermal cell wall
Midrib
Lamina
Adaxial
Abaxial
1.62 0.63 0.87 1.11 0.70 0.92 0.60 0.71 0.93 0.63 0.92 0.60 0.73 0.67 0.71 1.08
0.10 0.10 0.24 0.11 0.20 0.10 0.11 0.11 0.12 0.10 0.11 0.16 0.11 0.11 0.10 0.08
sinuous sinuous sinuous sinuous wavy–slightly sinuous sinuous sinuous sinuous sinuous wavy–straight sinuous sinuous sinuous wavy–slightly sinuous sinuous sinuous
wavy–straight sinuous sinuous sinuous sinuous sinuous sinuous wavy wavy wavy wavy–sinuous sinuous not observed wavy–slightly sinuous sinuous wavy
Mallotus dispar M¨uell. Arg. MIDRIB TS: U-shaped abaxially, adaxial surface nearly flat; thick-walled cells present below adaxial and abaxial epidermis. Vascular tissue with smaller bundles situated laterally to adaxial side of main system (Fig. 10B). Mallotus griffithianus Hook. fil. semi-circular abaxially, adaxial side flat (Fig. 10L). Adaxial surface raised over larger vascular bundles. PETIOLE TS: brachysclereids present in ground tissue (Fig. 6). MIDRIB TS:
Mallotus kingii Hook. f. LAMINA TS: vein endings sometimes with slightly enlarged tracheids. MIDRIB TS: semicircular abaxially, adaxial surface with low broad ridge; vascular tissue with a small central bundle (Fig. 10K). Mallotus leucodermis Hook. f. peltate trichomes in papilla-lined crypts (Fig. 5). MIDRIB TS: U-shaped abaxially, adaxial side slightly ridged; vascular tissue with no central bundles (Fig. 10N).
LAMINA TS:
Mallotus macrostachyus (Miq.) M¨uell. Arg. TS: adaxial epidermal cells conical in shape. Lamina bundles with parenchymatous girders to adaxial epidermis; vein endings with slightly swollen tracheids. Adaxial surface raised over larger vascular bundles. MIDRIB TS: U-shaped abaxially, adaxial side nearly flat with slight ridge; vascular tissue with one central bundle (Fig. 10I). Inner ground tissue with secretory cells.
LAMINA
Mallotus miquelianus (Scheff.) Boerl. adaxial surface bulging over large veins. MIDRIB TS: U-shaped abaxially,
LAMINA TS:
as high as wide to 3 times wider than high as high as wide to twice as wide as high 2–5 times wider than high 2–3 times wider than high as high as wide to 4 times wider than high 3–4 times wider than high 3–4 times wider than high as high as wide to twice as wide as high 1–4 times wider than high as high as wide to twice as wide as high 2–3 times wider than high
simple, multicellular with arms & stellate
—
—
peltate in papillalined crypts
stellate
simple, multicellular with arms & stellate
—
simple, multicellular with 2–3 arms
stalked stellate
simple, multicellular with arms
—
M. dispar
M. griffithianus
M. kingii
M. macrostachyus
M. miquelianus
M. oblongifolius
M. paniculatus
M. penangensis
M. peltatus
M. muticus
M. leucodermis
3–5 times wider than high
stalked stellate
M. barbatus
Adaxial
Species
twice as wide as high
as high as wide to twice as high as wide
twice as wide as high
2–3 times wider than high
3–4 times wider than high
2–3 times wider than high
2–3 times wider than high
2–3 times wider than high
2–3 times wider than high
2–3 times wider than high
once to twice as wide as high
3–5 times wider than high
Abaxial
Epidermal cell (size)
Trichomes (non-glandular)
just under half of leaf thickness
just under half of leaf thickness
outer layer just under half of leaf thickness
just under half of leaf thickness
just under quarter of leaf thickness
just under half of leaf thickness
just under half of leaf thickness
1/3 of leaf thickness
just under half of leaf thickness
just under half of leaf thickness
just under half of leaf thickness
more than half of leaf thickness
Palisade thickness
Lamina
5–6
4–6
1–2
4–5
6–7
3–4
2
7–10
4–5
5–6
3–4
2
Mesophyll (layers)
TABLE 4. Anatomical characters of some Mallotus Lour. (Euphorbiaceae) species
++
++
–
++
+
+
–
+
++
+++
–
+
Terminal sclereids
palisade, mesophyll
palisade mesophyll
mesophyll
in idioblasts
in idioblasts
*palisade
mesophyll
palisade infrequent
—
—
palisade, mesophyll
mesophyll
Druses
–
+
+
+
+
+
+
+
+
–
+
+
Idioblasts
146 K. H. HUSSIN ET AL
as high as wide to twice as wide as high 2–3 times wider than high as high as wide to twice as wide as high as high as wide to 3 times wider than high
simple, stellate in crypts
simple, unicellular and short
simple, unicellular and short
simple, multicellular with arms & stellate
M. philippensis
M. repandus
M. subpeltatus
as high as wide to twice as wide as high
2–3 times wider than high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
Abaxial
just under half of leaf thickness
just under half of leaf thickness
just under half of leaf thickness
1/3 of leaf thickness
Palisade thickness
3–4
4–5
3
2–8
Mesophyll (layers)
+
++
–
+
Terminal sclereids
palisade, mesophyll
palisade
in idioblasts
mesophyll
Druses
Terminal sclereids: + = infrequent, ++ = present, +++ = abundant; *Druses = both druse and solitary crystals present; Idioblasts: + = present, -ve = absent.
M. tilifolius
Species
Adaxial
Epidermal cell (size)
Trichomes (non-glandular)
Lamina
TABLE 4. continued
–
+
+
+
Idioblasts
LEAF ANATOMY OF MALLOTUS 147
phloem, parenchyma infrequent *phloem, *parenchyma —
phloem, *parenchyma phloem, parenchyma phloem, *parenchyma parenchyma, phloem infrequent phloem, solitary in parenchyma phloem, parenchyma phloem, solitary in parenchyma
stalked stellate
simple, armed & stellate
—
simple, infrequent
—
—
multicellular with arms
—
stalked stellate
simple, multicellular with arms and stellate
M. barbatus
M. dispar
M. griffithianus
M. leucodermis
M. macrostachyus
M. miquelianus
M. oblongifolius
M. paniculatus
M. peltatus
M. muticus
Druses
Trichomes
Species
Midrib
twice as wide as high
twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
twice as wide as high
as high as wide to twice as wide as high
Epidermal cell (size)
8–12
10
10–11
7–10
8–10
6–7
10–11
5–6
11–13
7–10
Outer parenchymatous tissue (layers)
2–3
6–9
1–3
1
1–2
6–11
13–16
1
1
13–16
Central bundles
Petiole
parenchyma
Druses
*parenchyma
phloem, parenchyma
*parenchyma infrequent
—
parenchyma
parenchyma
*parenchyma, phloem abundant
parenchyma infrequent
*parenchyma
TABLE 5. Anatomical characters of some Mallotus Lour. (Euphorbiaceae) species
simple & stellate
stellate
simple & stellate
simple unicellular, multicellular with arms
stellate
stalked stellate
—
simple, unicellular but infrequent
simple, multicellular with two-armed
stalked stellate
Trichomes
148 K. H. HUSSIN ET AL
*phloem, *parenchyma
*parenchyma, phloem parenchyma, phloem parenchyma, phloem parenchyma phloem
simple
simple, multicellular stellate
—
simple, multicellular with arms
—
M. penangensis
M. philippensis
M. repandus
M. subpeltatus
M. tiliifolius
*Druses = both druse and solitary crystals present
Druses
Trichomes
Species
Midrib
as high as wide to twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
as high as wide to twice as wide as high
one and a half times higher than wide to twice as wide as high
Epidermal cell (size)
TABLE 5. continued
11–13
8–9
6–7
8–10
7–8
Outer parenchymatous tisse (layers)
1
4
2
1
1
Central bundles
Petiole
parenchyma, phloem, solitary infrequent
parenchyma
parenchyma, phloem
phloem, *parenchyma
*parenchyma infrequent
Druses
simple, multicellular with two-armed
simple, unicellular, short, infrequent
simple, unicellular and short
simple unicellular, multicellular stellate
simple, unicellular
Trichomes LEAF ANATOMY OF MALLOTUS 149
150
K. H. HUSSIN ET AL
adaxial side nearly flat; vascular tissue consists of two main strands adaxially and abaxially with two small bundles situated laterally to main system (Fig. 10C). Mallotus muticus (M¨uell. Arg.) Airy Shaw MIDRIB TS: arc-shaped abaxially, adaxial side with sharp ridge; vascular tissue with no central bundles (Fig. 10M). Mallotus oblongifolius M¨uell. Arg. LAMINA TS: adaxial surface bulging over large bundles. MIDRIB TS: semi-circular abaxially, raised adaxially; strands of fibres present in adaxial ridge (Fig. 10F). Mallotus paniculatus (Lam.) M¨uell. Arg. LAMINA TS: vascular bundles with parenchymatous girders to adaxial epidermis; vein endings with swollen tracheids. Abaxial surface bulging over large vascular bundles. MIDRIB TS: U-shaped abaxially, adaxial side nearly flat; vascular tissue with one central bundle (Fig. 10D). Mallotus peltatus (Gessel.) M¨uell. Arg. abaxial surface bulge out over vascular bundles. MIDRIB TS: semi-circular abaxially, raised adaxially; vascular tissue in an interrupted ring (Fig. 10E).
LAMINA TS:
Mallotus penangensis M¨uell. Arg. vascular bundles with sclerenchymatous girders to adaxial epidermis. MIDRIB TS: semi-circular abaxially, adaxial side sharply raised; vascular tissue consisting of two main arcs, the larger one abaxially (Fig. 10H). PETIOLE TS: Glandular cells abundant in ground tissue, some with dark contents. LAMINA TS:
Mallotus philippensis (Lam.) M¨uell. Arg. LAMINA TS: trichomes in crypts (Fig. 8) in abaxial surface. Enlarged tracheids infrequent. Large vascular bundles with parenchymatous extension to adaxial epidermis. Adaxial surface raised over larger vascular bundles. MIDRIB TS: semicircular abaxially, adaxial side flat to slightly raised. Thick-walled parenchyma cells below adaxial epidermis and few layers to inside of abaxial epidermis. Vascular tissue with no central bundles (Fig. 10P). Mallotus repandus (Willd.) M¨uell. Arg. LAMINA TS: vein endings sometimes with enlarged tracheids, adaxial surface bulging over larger vascular bundles. MIDRIB TS: circular abaxially, raised adaxially; vascular tissue consisting of two main arcs with small lateral bundles, strands of fibres in ground tissue above vascular strand (Fig. 10G). Mallotus subpeltatus M¨uell. Arg. LAMINA TS: adaxial surface raised over larger vascular bundles. MIDRIB TS: U-shaped abaxially, adaxial side flat to slightly convex; vascular tissue with smaller bundles in centre region (Fig. 10 O). Mallotus tiliifolius M¨uell. Arg. LAMINA TS: abaxial surface bulging over vascular bundles.
MIDRIB TS:
U-shaped
LEAF ANATOMY OF MALLOTUS
151
abaxially, adaxial side flat; vascular tissue with smaller bundles situated laterally to adaxial side of main system (Fig. 10A).
DISCUSSION
Significant anatomical features Results of the study show that there is considerable anatomical variation between the 16 species of Mallotus studied. However, some characters are present in all of them. All have a single layer of palisade cells of variable height, except M. paniculatus which varies from one to two layers. A hypodermal layer was not seen in any of the species. Druses are present in enlarged cells (idioblasts) in the palisade layer of most species. In some species the druses are not only confined to the idioblasts but also occur in the palisade and spongy mesophyll cells. In the vascular tissue, druses are usually present in the parenchyma cells of the midrib of the leaves and petioles as well as in the phloem cells. In some species solitary crystals are also present. In all the specimens studied it was not possible to identify collenchyma cells in the midrib or petioles. In some species the cells are noticeably absent, but in others thickwalled parenchyma cells resembling collenchyma cells are present especially in herbarium specimens. Since these could probably be due to the shrinking effect of drying which was not reversed fully, their presence is reported as ‘not seen’. Another feature which was observed but needs confirmation is the presence of small cells to the inner side of the xylem tissue which are not lignified. In M. macrostachyus they occur in groups in the ground tissue in the middle of the midrib. These cells on close observation resemble phloem tissue but this needs verification. Paracytic stomata were observed for all the species except M. philippensis where the presence of persistent trichomes made it impossible to observe the stomata. The ‘rubiaceous’ or paracytic type is characteristic for the tribe Acalypheae (Metcalfe & Chalk, 1950) and forms the basic type for the family (Raju & Rao, 1977), although the anomocytic type is more common in Euphorbia species (Kakkar & Paliwal, 1972). On the underside of the lamina all species have glandular trichomes (Figs 1 & 3). In addition, non-glandular trichomes are also present except in M. kingii, M. griffithianus, M. muticus and M. penangensis. M. leucodermis has only peltate trichomes which is a useful diagnostic character. According to Solereder (1908) glandular hairs are more frequent in the Acalyphae than elsewhere in the Euphorbiaceae. In M. philippensis the presence of trichome-lined crypts on the underside of leaves is a diagnostic character for the species. The vein endings of the vascular system in all the species are of the dendroid type with two species having veins ending with swollen tracheids. These are M. macrostachyus, M. repandus, M. barbatus and sometimes M. philippensis. Such tracheids have been observed in some genera of the Euphorbiaceae (Metcalfe & Chalk, 1950). In some species terminal sclereids are frequent to abundant. This may be similar to the ‘sclerenchymatous elements’ as reported by Metcalfe & Chalk (1950) for a few species of other genera in the family as well as to the ‘filiform’ sclereids observed in Dicoelia affinis and several Cleistanthus species of the Phyllanthoideae (Levin, 1986).
152
K. H. HUSSIN ET AL
According to Solereder (1908) “sclerenchymatous fibres running freely in the leaf are found chiefly in the tribe Acalypheae”. The presence of leaf sclereids may be useful in taxonomy. Their occurrence in Androstachys johnsonii (ex-Euphorbiaceae) supports the separation of the genus into the family Androstachydaceae (Alvin & Rao, 1987). The outer walls of the adaxial epidermal cells in the lamina of M. macrostachyus are conical in shape. This feature was not observed in the rest of the species and hence is diagnostic for M. macrostachyus. The vascular bundles in the lamina of M. paniculatus, M. macrostachyrus, M. barbatus and M. philippensis have parenchymatous extensions to the adaxial epidermis. In M. penangensis these extensions consist of sclerenchyma. This feature has been observed for a few Euphorbia species (Metcalfe & Chalk, 1950). For most of the species of Mallotus studied except M. leucodermis, M. kingii, M. muticus and M. penangensis the adaxial surface bulges out over the larger vascular bundles. Transverse sections of midribs reveal variations in the shape of the adaxial and abaxial surfaces. The adaxial surface varies from flat to slightly concave, convex and ridged. The ridge is very prominent in M. peltatus, M. oblongifolius, M. repandus, M. penangensis and M. muticus while in M. macrostachyus and M. barbatus this ridge is much lower. The abaxial surface shows slight variations, which when combined together with the adaxial surface, may be diagnostic for certain species such as M. muticus. The vascular tissue of the midrib is of the interrupted ‘O’ type. Transverse sections of midribs show some variations between species (Fig. 10). In some species central bundles are present as in M. paniculatus, M. barbatus, M. kingii and M. macrostachyus while in M. tiliifolius, M. dispar and M. subpeltatus the adaxial strand of the vascular tissue is broken into several bundles. The structure of the midrib in transverse section is therefore a useful character in the systematic anatomy of the genus. The general vascular system in the petiole is of the ‘O’ type vascular strand. However, while central bundles are present in the midrib of certain species only, they are present in the petioles of all species but the number varies between species (Fig. 11). M. miquelianus, M. tiliifolius, M. dispar, M. penangensis, M. kingii, M. griffithianus, M. muticus, M. leucodermis and M. philippensis, have one large central bundle. In M. peltatus, M. oblongifolius, M. repandus and M. subpeltatus there are two to four small bundles while in M. paniculatus, M. macrostachyus and M. barbatus the number ranges from six to sixteen. In species with more than one central bundle the number of these bundles varies between specimens. The range in number rather than the exact figure is more useful taxonomically. In M. graffithianus there are brachysclereids present in the parenchyma tissue and this can be a useful diagnostic character. Taxonomic implications of characters These anatomical characters in combination are very useful in the identification of Mallotus species. The results however do not show any clustering of characters which could be used to classify the genus into broad groups. With respect to sectional groupings as made by Ridley (1924) and Airy Shaw (1973), M. tiliifolius and M. dispar which are classified into the same section, S. Echinocroton (Ridley, 1924) and S. Rottleropsis (Airy Shaw, 1973) have nearly similar midrib structure in transverse sections. Both have only one central bundle in the petiole. Similarly, M. macrostachyus and M. barbatus which are both put in the Section Echinus by Ridley are quite similar in the midrib structure. Anatomical data in this case support the placing of those
LEAF ANATOMY OF MALLOTUS
153
species into the respective sections. In the other sections anatomical characters do not support the classification. According to Airy Shaw (1973) in his treatment of the Bornean species, M. griffithianus is related to M. kingii of peninsular Malaysia. Anatomically, they share some common characters such as the presence of terminal sclereids and a large central bundle in the petiole. Both have glandular trichomes only on the lamina. However transverse sections of the midrib show differences in the adaxial surface and the presence of a central bundle in M. kingii. This supports the placing of the two species into different sections by Ridley (1924). Results of this study also do not show any correlation of anatomical characters exclusively for M. muticus and M. leucodermis which according to Whitmore (1973) and Airy Shaw (1973) are very similar in all respects except in the character of the fruit.
ACKNOWLEDGEMENTS
The authors wish to thank Dr D.F. Cutler of Jodrell Laboratory, Kew Gardens for critical reading of the manuscript and Ahmed Zainudin Ibrahim, Hamid Salleh and Sukaimi Rasmi for their technical help. This work was partly supported by IRPA grant (4-07-03-007).
REFERENCES Airy Shaw HK. 1973. The Euphorbiaceae of Borneo. Kew Bull. Additional Services IV, London: HMSO. Alvin KL, Rao TA. 1987. On the unusual distribution pattern of leaf sclereids in Androstachys johnsonii Prain (Euphorbiaceae). Botanical Journal of the Linnean Society 95: 55–60. Corner EJH. 1952. Wayside Trees of Malaya. 2nd edn. Vol 1. Singapore: Government Printer. Kakkar L, Paliwal GS. 1972. Studies on the leaf anatomy of Euphorbia V. Epidermis. Proceedings of the Indian National Science Academy, B 40: 55–67. Levin GA. 1986. Systematic foliar morphology of Phyllanthoideae (Euphorbiaceae). I. Conspectus. Annals of the Missouri Botanical Gardens 73: 29–85. Metcalfe CR, Chalk L. 1950. Anatomy of the Dicotyledons. Vol 1. Oxford: Clarendon Press. Raju VS, Rao PN. 1977. Variation in the structure and development of foliar stomata in the Euphorbiaceae. Botanical Journal of the Linnean Society 75: 69–97. Ridley HN 1924. Flora of the Malay Peninsula. Vol. III. London: L. Reeve & Co. Sehgal L, Paliwal GS. 1974. Studies on the leaf anatomy of Euphorbia VII. General conclusions and systematic considerations. Phytomorphology 24: 141–151. Solereder H. 1908. Systematic Anatomy of the Dicotyledons. Transl. L.A. Boodle & F.E. Fritsch. Oxford: Clarendon Press. Whitmore TC. 1973. Tree Flora of Malaya, A Manual for Foresters, vol 2. Kuala Lumpur: Longman.