A new species of Polygala (Polygalaceae) from ultramafic soils in Sekhukhuneland, South Africa, with notes on its ecology

Available online at www.sciencedirect.com

South African Journal of Botany 76 (2010) 345 – 353 www.elsevier.com/locate/sajb

A new species of Polygala (Polygalaceae) from ultramafic soils in Sekhukhuneland, South Africa, with notes on its ecology S.J. Siebert a,⁎, E. Retief b , A.E. Van Wyk c , M. Struwig a a

A.P. Goossens Herbarium, School of Environmental Sciences and Development, North-West University, Private Bag X6001, Potchefstroom 2520, South Africa b National Herbarium, South African National Biodiversity Institute, Private Bag X101, Pretoria 0001, South Africa c H.G.W.J. Schweickerdt Herbarium, Department of Plant Science, University of Pretoria, Pretoria 0002, South Africa Received 14 August 2009; received in revised form 7 January 2010; accepted 14 January 2010

Abstract Polygala sekhukhuniensis Retief, Siebert & A.E.Van Wyk (Polygala; section Polygala; subsection Heterolophus), a new species with a restricted range in Sekhukhuneland, South Africa, is described, illustrated and compared with other members of the genus. It is a dwarf shrub that can be distinguished by its much-branched habit, sparsely flowered inflorescences, pink alae with darker pink veins, brown to black seed testa, and oblate pollen grains with pronounced opercula. Geographically, P. sekhukhuniensis is confined to heavily eroded localized sites, a natural geomorphological feature of some of the highly water-dispersible soils derived from ultramafic rocks in the valleys of the Steelpoort River and its tributaries in the Sekhukhuneland Centre of Plant Endemism. P. sekhukhuniensis is a calciotrophic excluder of heavy metals that accumulates Ca in its leaves. It is ecologically compared with co-occurring species of Polygala on ultramafic-derived soil. © 2010 SAAB. Published by Elsevier B.V. All rights reserved. Keywords: Bushveld Complex; Caruncle; Endemism; Heavy metals; Palynology; Sekhukhuneland Centre of Endemism; Taxonomy; Ultramafic rocks

1. Introduction Since the pioneering work of Wild (1965) on plants associated with soils rich in heavy metals and derived from ultramafic rocks in southern Africa, and subsequent groundbreaking research on plant-soil associations on southern African serpentinites by Morrey et al. (1989), Williamson et al. (1997) and Balkwill and Campbell-Young (2001), many plant species new to science have been described from such substrates. In recent years the Sekhukhuneland Centre of Plant Endemism (SCPE) in South Africa has been highlighted as an area harbouring potential new plant species (Van Wyk and Smith, 2001). Siebert et al. (2001) showed that the high levels of plant endemism of this region are significantly correlated with the heavy metal soils derived from ultramafic rocks. In the last three years, six new endemic plant species (including a new monotypic genus, Prototulbaghia) were described from the SCPE (Venter et al., 2007; Vosa, 2007; Burrows and Burrows, ⁎ Corresponding author. E-mail address: [email protected] (S.J. Siebert).

2008; Hankey et al., 2008; Retief et al., 2008; Manning and Goldblatt, 2009). Massoura et al. (2004) have shown that plant species adapted to heavy metal soils often accumulate or exclude metals that are present in the soil at high concentrations. This physiological adaptation is usually also expressed in the morphology through ecological speciation (Balkwill and Campbell-Young, 2001; Retief et al., 2008). Subsequent studies on heavy metal accumulation by plants in the SCPE by Mandiwana et al. (2007) have revealed several metal accumulators and excluders. Such species are known to be genetically different from their widespread congeners (Yang et al., 2005). This has warranted taxonomic investigation into one such excluder that is tolerant of soils rich in heavy metals, a member of Polygala that was initially considered an ecotype of P. leptophylla Burch. var. leptophylla. However, subsequent field work and comparative morphological studies have shown the putative ecotype to be a distinct new species related to members of section Polygala, subsection Heterolophus (Paiva, 1998), specifically P. hottentotta Presl., P. leptophylla var. leptophylla and P. seminuda Harv. It is confined to areas of highly water-dispersible soils derived from

0254-6299/$ - see front matter © 2010 SAAB. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sajb.2010.01.003

346

S.J. Siebert et al. / South African Journal of Botany 76 (2010) 345–353

ultramafic rocks. The new species is here described as Polygala sekhukhuniensis Retief, Siebert & A.E.Van Wyk. This is the second excluder of heavy metals, after Euclea sekhukhuniensis (Retief et al., 2008), that is strictly confined to localized areas of naturally eroded, ultramafic soils in Sekhukhuneland. The aim of this paper is to describe and name the new taxon, and highlight the morphological, palynological and ecological differences between the taxon and its most closely related congeners. 2. Materials and methods 2.1. Morphological assessment Live material of the new species was extensively studied in the field. Its morphology was compared to existing descriptions and treatments of the genus (Exell, 1960; Paiva, 1998). Specimens of Polygala housed in the National Herbarium (PRE), Pretoria and H.G.W.J. Schweickerdt Herbarium (PRU), University of Pretoria, were examined to gather quantitative and qualitative data on morphology, phenology and distribution of the new species, as well as related taxa. Micrographs of seed were taken with a Nikon Digital Camera DXM 1200 F fitted on a Nikon SMZ 1500 stereomicroscope. Seed terminology follows Paiva (1998). 2.2. Palynological assessment Mature, unopened flower buds from herbarium specimens were dissected to obtain anthers with pollen. Unacetolyzed pollen grains were mounted onto aluminium stubs, sputtercoated with gold/palladium (Au/Pd) and examined with a FEI Quanta 200 ESEM Scanning Electron Microscope (SEM). Ten pollen grains per species were measured for polar length (P) and equatorial width (E). Palynological terminology follows Punt et al. (1994). 2.3. Plant-soil assessment Plant material of the new species and P. hottentotta, as well as soil samples were collected during early summer, environmental factors were noted and associated plant communities identified (Siebert et al., 2002). Samples were taken at ten sites, five each dominated by either species. Soil analyses was done with X-Ray Fluorescence (XRF) Spectrometry and plant analyses with Atomic Absorption Spectrophotometry (AAS) as well as Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Terminology describing exclusion mechanisms follows Massoura et al. (2004). 3. Taxonomy The subcosmopolitan family, Polygalaceae, comprises about 19 genera and 925 species (Mabberley, 1997). The flowers are superficially similar to those of members of the subfamily Papilionoideae (Fabaceae). However, the wings (alae) of Polygala flowers belong to the calyx and not to the corolla. The standard is completely different and Polygala has a crest at the tip of the keel. Currently various studies (Prenner, 2004; Banks

et al., 2008) confirm the placing of the erstwhile order Polygalales in an expanded order Fabales (APG II, 2003). In the Flora of southern Africa region, the genus Polygala is represented by ± 88 species (Bredenkamp, 2000), of which ten are currently known from the SCPE. Polygala sekhukhuniensis Retief, Siebert & A.E.Van Wyk, sp. nov.; fruticulus pumilus caulibus patentibus caudice lignoso; caules foliaque sparse apprese hirsuti; folia spiraliter disposita, lamine linearo-oblonge vel obovata, apice mucronata; calyx sepalis duobus aliformibus, alis roseis; corolla carina cristata, crista atrorosea vel purpurea. Type. — 2430 (Pilgrim's Rest): Mpumalanga, Thornecliffe Chrome Mine, turn off from Lydenburg-Sekhukhune road, [1 December 1997], Van Wyk 13031 (PRU, holo.; PRE, iso.). Rigid perennial shrublet, 0.2–0.4 m high, with a woody rootstock; stems and leaves sparsely adpressed-hairy; hairs unbranched. Stems usually more than four from rootstock, erect and spreading, branched, woody at base; young branches green, herbaceous. Leaves spirally arranged, shortly petiolate; petiole up to 0.75 mm long; blade linear-oblong or obovate, 7–15 × 1.0– 2.5 mm, apex obtuse, occasionally acute, mucronate, margin entire. Inflorescences comprising terminal racemes, peduncle up to 80 mm long, pedicels 1.75 mm long. Flowers irregular; bisexual, drooping. Calyx pentamerous, with sepals unequal, three outer ones sepaloid, two inner ones petaloid, larger winglike, 6–8 × 3.5–5.0 mm, all free; wings pink with darker pink veins. Corolla of five petals, lowest one forming a carina, crested, crest dark pink to purple, two lateral ones usually vestigial or absent, two upper ones joined at base to carina and staminal tube. Stamens eight, basally fused for ±two-thirds their length. Ovary superior, two locular. Fruit a laterally compressed capsule, up to 6.5 mm long, membranous, edges wing-like, 0.25 mm wide, deeply notched at apex, 2-seeded. Seed 4.5 × 1.5 mm, ellipsoid, caruncle oblique, appendages poorly developed, single one membranous, paired ones chitinous; indumentum silky white, ±1 mm longer than seed; testa dark-brown to black. Flowering time: November to June. (Fig. 1). 3.1. Diagnostic characters and key to species Polygala sekhukhuniensis and two related species, P. hottentotta and P. leptophylla, are distinguished from P. seminuda and the rest of the genus by their narrowly ovate leaves, free anterior sepals, terminal racemes, wings not more than 6 mm broad, and the carina 6 mm long with crest 1–3 mm long. P. sekhukhuniensis and P. leptophylla differ from P. hottentotta, with the latter one having longer peduncles (124 mm versus 78– 90 mm), greater number of flowers per raceme (23 versus 7–12), larger flowers (wing length 7.8 mm versus 6.8–7.0 mm), and smaller seed (4.3 × 1.5 mm versus 5.6–5.9 × 1.9 mm) (Table 1). Morphologically P. sekhukhuniensis most closely resembles P. leptophylla var. leptophylla, however, the leaf size of the former is 7–15 × 1–2.5 mm, whereas the leaves of the latter one are 14–22 × 1.5–3 mm (Table 1). Flowers of P. sekhukhuniensis differ from P. leptophylla var. leptophylla in the crest of the former being purple and the alae pink with darker pink veins, whereas the crest is white, pink or purple in the latter, with the

S.J. Siebert et al. / South African Journal of Botany 76 (2010) 345–353

347

Fig. 1. Polygala sekhukhuniensis. (A) Flowering plant, showing habit of above-ground parts; (B) Mature leaf; (C) Flower, lateral view; (D) Flower, lateral view with wing-like sepal removed; (E) Old flower, lateral view with wing-like sepal removed to show capsule; (F) Ovary with style and stigma; (G) Androecium, showing staminal tube joined at base to two upper petals; (H) Seed. Voucher: Van Wyk 13031. Scale bar 10 mm (A), 2 mm (B–E), or 1 mm (F–H). Artist: Daleen Roodt.

Table 1 Mean measurements of selected morphological characters in Polygala sekhukhuniensis and three closely related species (n = 10/species). Polygala sekhukhuniensis Number of flowers per raceme Inflorescence (mm) Peduncle length

Polygala leptophylla

Polygala hottentotta

Polygala seminuda

7 ± 1.3

12 ± 1.3

23 ± 7.4

11 ± 2.3

78 ± 23

90 ± 18

124 ± 27

86 ± 24

Flowers (mm) Wing length Wing breadth

6.8 ± 0.6 4.1 ± 0.7

7.0 ± 0.8 3.5 ± 0.5

7.8 ± 0.8 4.0 ± 0.7

6.7 ± 1.1 3.7 ± 0.9

Leaves (mm) Length Breadth

11 ± 2.2 1.4 ± 0.5

19 ± 3.0 2.1 ± 0.5

21 ± 5.9 1.4 ± 0.8

20 ± 2.3 1.4 ± 0.5

Seed (mm) Length Breadth Caruncle

5.6 ± 0.7 1.9 ± 0.5 3.1 ± 0.8

5.9 ± 0.9 1.9 ± 0.4 3.0 ± 0.7

4.3 ± 0.4 1.5 ± 0.7 2.2 ± 0.5

6.3 ± 1.1 1.7 ± 0.5 3.5 ± 0.7

alae whitish to yellowish with green veins. Seeds of P. sekhukhuniensis differ from P. leptophylla var. leptophylla in the colour of the testa, dark brown-black versus reddish-brown, the bare patch on the testa between the caruncle and the indumentum (the size, 0.3 × 0.6 mm versus 1.2 × 1.5 mm), and the caruncular appendages, poorly developed (0.2 versus 0.8 mm long) (Fig. 2; Table 1). Key to the species of Polygala in Sekhukhuneland 1a. Plants procumbent, up to 50 mm high 1b. Plants erect, 50 mm to 1.5 m high 2a. Anterior sepals united for at least half their length 2b. Anterior sepals free or only slightly joined at the base 3a. Flowers solitary or in lateral racemes 3b. Flowers in terminal racemes, sometimes with additional lateral racemes 4a. Flowers presented in a raceme, 30–140 mm long 4b. Flowers solitary, borne in leaf axils 5a. Wings 7–15 mm broad; sturdy, erect shrublets up to 2 m tall 5b. Wings less than 6 mm broad; slender, annual or perennial herbs up to 0.5 m tall

P. krumanina 2 P. uncinata 3 4 5 P. sphenoptera P. gerrardii P. virgata 6

(continued on next page)

348

S.J. Siebert et al. / South African Journal of Botany 76 (2010) 345–353

Fig. 2. Stereomicroscope micrographs of seed and caruncle. (A) Polygala sekhukhuniensis, membranous appendage (me) 2.9 mm and chitinous appendage (ch) 0.8 mm, hairs cover seed surface completely; (B) P. leptophylla var. leptophylla, me 2.7 mm and ch 1.6 mm, hairs cover two-thirds of the seed surface; (C) P. hottentotta, me 2.1 mm and ch 1.0 mm, hairs cover seed surface completely; (D) P. seminuda, me 3.8 mm and ch 2.5 mm, hairs cover half of the seed surface. Scale bars 1 mm.

6a. Stems greyish; carina 3 mm long with crest 1 mm long 6b. Stems green; carina 6 mm long with crest up to 3 mm long 7a. Racemes longer than 100 mm; pedicels 2–3 mm long 7b. Racemes shorter than 100 mm; pedicels 1–2 mm long 8a. Flowers crowded in terminal clusters on raceme 8b. Flowers evenly spaced along entire raceme 9a. Leaves 16–22 × 1.5–3.0 mm, apex acute; flowers with crest white, pink or purple, alae whitish to yellowish with dark green veins 9b. Leaves 9–15 × 1.0–2.5 mm, apex obtuse or retuse; flowers with crest purple, alae pale pink with dark pink veins

P. seminuda 7 P. hottentotta 8 P. gracilenta 9 P. leptophylla

P. sekhukhuniensis

3.2. Palynology In a review of Polygala palynological literature (Banks et al., 2008), no mention is made of descriptions, drawings, or micrographs of pollen belonging to the species compared in this paper. Hence, the SEM observations on pollen grains presented here are the first for the four taxa concerned (Fig. 3). Pollen of P. sekhukhuniensis is isopolar and spheroidal in equatorial view; P × E = (23)–25.64–(27) × (24)–25.06–(26) μm; P/E = 1.02 (Table 2). Apertures 22, zonocolporate.

S.J. Siebert et al. / South African Journal of Botany 76 (2010) 345–353

349

Fig. 3. SEM micrographs of pollen. Polar view to the left. (A) Polygala sekhukhuniensis; (B) P. leptophylla var. leptophylla; (C) P. hottentotta; (D) P. seminuda. Scale bars 10 μm.

Ectoapertures (17)–18.6–(21) × (1)–1.2–(3) μm; endoapertures (1)–4.8–(6) μm × endocingulate. Surface ornamentation psilate to finely granular, with scattered lumina in apocolpial areas that are small (less than 1 μm). Opercula present. Pollen grains of P. sekhukhuniensis, and P. hottentotta differ from P. leptophylla var. leptophylla and P. seminuda in shape,

namely oblate versus prolate and prolate-spheroidal respectively (Fig. 3). Opercula over the endoapertures of P. sekhukhuniensis, P. hottentotta and P. seminuda are pronounced, mostly so in the new species (Fig. 4). Although the shape of pollen grains of P. sekhukhuniensis and P. hottentotta are very similar, the former has smaller grains (Table 2).

350

S.J. Siebert et al. / South African Journal of Botany 76 (2010) 345–353

Table 2 Mean measurements (μm)/counts of selected pollen characters of Polygala sekhukhuniensis and three closely related species (n = 10/species).

Nr. of apertures Polar length Equatorial breadth P/E Polar diameter Ectoapertures l x w Endoapertures l x w

Polygala sekhukhuniensis

Polygala leptophylla

Polygala hottentotta

Polygala seminuda

22 25.64 ± 1.3 25.06 ± 0.9 1.02 14.79 ± 1.3 18.6 × 1.2 4.8 × endocingulate

20 40.54 ± 2.9 25.98 ± 1.8 1.56 18.25 ± 3.7 30.6 × 0.8 2.1 × endocingulate

21 30.29 ± 1.2 33.27 ± 1.4 0.91 16.84 ± 1.3 22.9 × 1.1 6.9 × endocingulate

21 33.34 ± 3.9 29.66 ± 1.5 1.12 17.93 ± 1.5 26.4 × 1.3 5.3 × endocingulate

Fig. 4. Known distribution of Polygala sekhukhuniensis.

3.3. Distribution and ecology Polygala sekhukhuniensis is only known from Sekhukhuneland (Fig. 4). P. sekhukhuniensis and P. hottentotta occur on patches of anomalous soils in this region — sparsely vegetated soils that are mineralized and rich in heavy metals (Table 3). These soils are clayey and highly erodible, in contrast to the rocky, sandy soil on mountain slopes that is preferred by P. leptophylla var. leptophylla. These anomalies are akin to erosion gulleys, but in this case not due to human disturbance, but caused by natural erosion processes due to a weak soil structure and associated high water dispersability (Mason, 1959). According to Siebert et al. (2002) and Mandiwana et al. (2007), plant communities typical of these eroded sites in Sekhukhuneland include heavy metal accumulating or excluding species (Table 4). Polygala sekhukhuniensis is such a species, specifically adapted to grow in erosion gulleys of exposed heavy metal contaminated (ultramafic) soil. Hence, the opinion that the ecological species concept is an essential part of the biological species concept (Grant, 1992) is supported here. Asymmetry and within-plant variance are higher between specimens of the same

species in the contact zone between ultramafic and normal soils (Alados et al., 1999). This variance provides genetic material for natural selection and subsequent reproductive isolation. In the case of P. sekhukhuniensis, an open niche with an anomalous Ca-rich substrate (14.68% = 146 800 ppm) in an otherwise typical environment of soils rich in Mg (8.48% = Table 3 Environmental variables unique to plant communities containing either Polygala sekhukhuniensis or P. hottentotta in the Sekhukhuneland Centre of Plant Endemism. Characteristics

P. sekhukhuniensis

P. hottentotta

Slope (°) Aspect Rock cover (%) Rock size (mm) Soil type

4 (0–7) N, S, E, W 30 (5–55) 150 (100–500) Valsrivier, Prieska, Mayo, Bonheim Norite, pyroxenite, gabbro, alluvium Footslope, valley Tall, sparse shrubland

8 (0–15) S, W 45 (20–70) 450 (300–1500) Glenrosa, Mispah, Valsrivier Pyroxenite, magnetite

Geology Topographical position Vegetation type

Footslope, crest Short, open shrubland

S.J. Siebert et al. / South African Journal of Botany 76 (2010) 345–353 Table 4 Prominent associated taxa recorded for plant communities containing either Polygala sekhukhuniensis or P. hottentotta in the Sekhukhuneland Centre of Plant Endemism (Siebert et al., 2002). Life forms

Grass layer

Forb layer

Shrub layer

Tree layer

Species dominant in: P. sekhukhuniensis community

P. hottentotta community

Aristida congesta Fingerhuthia africana Stipagrostis hirtugluma Aloe cryptopoda Dicoma gerrardii Gnidia polycephala Euclea sekhukhuniensis Grewia vernicosa Searsia keetii Acacia sp. nov. Euphorbia tirucalli

Diheteropogon amplectens Loudetia simplex Themeda triandra Berkheya insignis Jamesbrittenia macrantha Petalidium oblongifolium Searsia sekhukhuniensis Tinnea rhodesiana Vitex obovata Bolusanthus speciosus Combretum hereroense

84 800 ppm) and poor in Ca (2.13% = 21 300 ppm) (Fig. 5A), probably favoured speciation. Similar to limestone, the soils inhabited by P. sekhukhuniensis have a high Ca:Mg ratio (2:1), which differ significantly from the soil substrate of P. hottentotta (1Ca:4 Mg) in the study area (Fig. 5A). As a consequence P. sekhukhuniensis has a leaf Ca:Mg ratio of 16:1, and P. hottentotta a ratio of 4:1 (Fig. 6A). O'Dell et al. (2006) have shown that the ability to maintain high leaf Ca:Mg is a key

351

evolutionary change needed for survival on heavy metal soil and represents the physiological feature distinguishing the plant species adapted to heavy metal soils from their non-adapted congeners. Furthermore, soils in which the two Polygala taxa grow have high concentrations of total Cr, Al and Fe (Fig. 5A,B), with Polygala hottentotta holding higher concentrations of Al and Fe in its roots, stems and leaves, but not at levels that could be considered as accumulating (Fig. 6B). P. sekhukhuniensis excludes these metals more effectively, despite the associated soil concentrations being higher (Fig. 5B). Overall it seems that P. sekhukhuniensis is the better excluder of heavy metals due to higher leaf Ca concentrations as a previously confirmed protection and survival mechanism (Konstantinou and Babalonas, 1996). It is suggested that P. sekhukhuniensis originated as an ecotype of and has developed from its suggested closest relative, P. leptophylla, which occurs on nearby mountain slopes. This theory was already proposed for Sekhukhuneland endemics by Knowles and Witkowski (2000), suggesting that the genetic properties of individuals occurring on iron-rich mountain slopes have the potential to immigrate to, adapt to and colonize ultramafic soils rich in heavy metals. It is hypothesized that P. sekhukhuniensis is a typical edaphic specialist which may well have speciated recently, after the Pleistocene (Reeves et al., 1983). It probably prefers the competition-free, open

Fig. 5. Chemical analyses of five soil samples collected from the root zone (300 mm deep) for each of Polygala sekhukhuniensis and P. hottentotta. Bulked sample per species.

352

S.J. Siebert et al. / South African Journal of Botany 76 (2010) 345–353

Fig. 6. Chemical analyses of plant material from five individuals each of Polygala sekhukhuniensis and P. hottentotta (young and old growth). Bulked sample per species.

niches of eroded, toxic ultramafic soils where it has a physiological advantage requiring high levels of Ca to tolerate heavy metals (Fig. 6A). P. sekhukhuniensis, like Euclea sekhukhuniensis, can therefore be considered a heavy metal excluding, calciotrophic species. 3.4. Conservation status Polygala sekhukhuniensis has a small geographical range in Sekhukhune Plains Bushveld (Siebert et al., 2002), and limited area of occupancy within natural erosion gulleys (dongas). Most of its habitat is under threat from slimes dams and rock dumps associated with the mining industry, as these eroded areas are considered to be of low conservation status. P. sekhukhuniensis is not formally protected in any conservation area. Populations of the species should therefore be closely monitored and its Red Data List assessment assessed. The conservation value of P. sekhukhuniensis is considered relatively high, as it could possibly be used as a keystone species in the ecology of mine dumps due to its internal mechanism of excluding heavy metals. 3.5. Etymology, vernacular names and uses The specific epithet refers to the geographical area the species occurs in, namely Sekhukhuneland, a region named for

King Sekhukhune(-i) I (1814–1882) of the Bapedi tribe. For consistency, and in line with existing Latin epithets of plants named after the region, it is based on the alternative spelling, “Sekhukhuniland”. We would like to propose the names “sekhukhune milkwort” and “sekhukhunebloukappie” as English and Afrikaans vernacular names, respectively. The recorded Northern-Sotho names for the plant are mabošêkgo and mogaletsaoi, which differs from the vernacular name, peloterri, given to the closely related P. leptophylla var. leptophylla. Burnt ashes are mixed with snuff for flavouring (Barnard 209) and the roots are cooked and given to forgetful people to make the mind sensible (Barnard 135). 3.6. Additional specimens examined LIMPOPO. — 2429 (Zebediela): Mankopanie, Farm Hoeraroep (–BD), Barnard 209 (PRE); Bewaarkloof, Potlake Nature Reserve (–BD), Van Rooyen 2339 (PRE); Potlake Nature Reserve (–BD), Matthée 1044 (PRU); Farm Geeneinde, Sekukuniland (– DB), Barnard & Mogg 737 (PRE); Sekhukhuniland, Farm Parys (–DB), Barnard & Mogg 738 (PRE). MPUMALANGA. — 2430 (Pilgrim's Rest): Maandagshoek (–CA), Kritzinger 118 (PRE, PRU); Steelpoort, Eastern Chrome Mines, valley beneath mountain in the Winterveld mine area

S.J. Siebert et al. / South African Journal of Botany 76 (2010) 345–353

(–CA), Siebert 449 (PRU); Sekukuni (–CC), Barnard 135 (PRE); Dwarsrivier, 5 km on turn-off to Lydenburg from Stofberg-Steelpoort road (–CC), Jordaan 782 (PRE); 2 km from Spitskop turn-off south on Steelpoort-Lydenburg road (– CC), Burgoyne 6015 (PRE); Thornecliffe Chrome Mine, hill west of office (–CC), Van Wyk & Siebert 12982 (PRU); Steelpoort, Ferrochrome Holdings, 4 km to east of Spitskop on way to Roossenekal (–CC), Siebert 337 (PRU); Turnoff to Thornecliffe Mine from Lydenburg, Steelpoort road (–CC), Van Wyk & Siebert 13311 (PRU); Road between Steelpoort and Kennedy's Vale (–CC), Siebert & Van Wyk 1379 (PRU). Acknowledgements The authors are indebted to Maggi Loubser, Geology Department, University of Pretoria, for assistance with XRF analyses and to Nina van Vliet, Department of Soil, Climate and Water, Pretoria, for assistance with AAS and ICP-MS analyses. We would like to thank Hugh Glen, for translating the diagnoses into Latin, Kevin Balkwill for constructive comments on a draft of the manuscript, Hester Steyn, for preparing the distribution map and Daleen Roodt for the line drawings. The National Research Foundation, University of Pretoria and South African National Biodiversity Institute provided financial support. References Alados, C.L., Navarro, T., Cabezudo, B., 1999. Tolerance assessment of Cistus ladanifer to serpentine soils by developmental stability analysis. Plant Ecology 143, 51–66. Angiosperm Phylogeny Group (APG) II, 2003. An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141, 399–436. Balkwill, K., Campbell-Young, G.J., 2001. Taxonomic studies in the Acanthaceae: Peristrophe serpenticola — a new species from the Great Dyke, Zimbabwe. South African Journal of Science 97, 551–554. Banks, H., Klitgaard, B.B., Claxton, F., Forest, F., Crane, P.R., 2008. Pollen morphology of the family Polygalaceae (Fabales). Botanical Journal of the Linnean Society 156, 253–289. Bredenkamp, C.L., 2000. Polygalaceae (Rosidae–Polygalales). In: Leistner, O.A. (Ed.), Seed plants of southern Africa: families and genera. : Strelitzia, vol. 10. National Botanical Institute, Pretoria, p. 450. Burrows, S.M., Burrows, J.E., 2008. Three new species of Asparagus (Asparagaceae) from South Africa, with notes on other taxa. Bothalia 38, 23–29. Exell, A.W., 1960. Polygalaceae. Flora Zambesiaca 1, 303–336. Grant, V., 1992. Comments on the ecological species concept. Taxon 41, 310–312. Hankey, A., Buys, M.H., Lebatha, P.D., 2008. Drimiopsis linioseta, a new species from the Sekhukhuneland Centre of Endemism, South Africa. Bothalia 38, 72–74. Knowles, L., Witkowski, E.T.F., 2000. Conservation biology of the succulent shrub, Euphorbia barnardii, a serpentine endemic of the Northern Province, South Africa. Austral Ecology 25, 241–252.

Edited by B-E Van Wyk

353

Konstantinou, M., Babalonas, D., 1996. Metal uptake by Caryophyllaceae species from metalliferous soils in northern Greece. Plant Systematics and Evolution 203, 1–10. Mabberley, D.J., 1997. The plant-book. Cambridge University Press, Cambridge. Mandiwana, K.L., Panichev, N., Kataeva, M., Siebert, S.J., 2007. The solubility of Cr(III) and Cr(VI) compounds in soil and their availability to plants. Journal of Hazardous Materials 147, 540–545. Manning, J.C., Goldblatt, P., 2009. Three new species of Gladiolus (Iridaceae) from South Africa, a major range extension for G. rubellus and taxonomic notes for the genus in southern and tropical Africa. Bothalia 39, 37–45. Mason, R., 1959. Later Pleistocene stratigraphy in the Transvaal. South African Archaeological Bulletin 14, 3–8. Massoura, S.T., Echevarria, G., Leclerc-Cessac, E., Morel, J.L., 2004. Response of excluder, indicator, and hyperaccumulator plants to nickel availability in soils. Australian Journal of Soil Research 42, 933–938. Morrey, D.R., Balkwill, K., Balkwill, M.-J., 1989. Studies on serpentine flora: preliminary analyses of soils and vegetation associated with serpentine rock formations in the southeastern Transvaal. South African Journal of Botany 55, 171–177. O'Dell, R.E., James, J.J., Richards, J.H., 2006. Congeneric serpentine and nonserpentine shrubs differ more in leaf Ca:Mg than in tolerance of low N, low P, or heavy metals. Plant and Soil 280, 49–64. Paiva, J.A.R., 1998. Polygalarum Africanarum et Madagascariensium prodromus atque gerontogaei generic Heterosamara Kuntze, a genere Polygala L. segregate et a nobis denuo recepti, synopsis monographica. Fontqueria 50, 1–346. Prenner, G., 2004. Floral development in Polygala myrtifolia (Polygalaceae) and its similarities with Leguminosae. Plant Systematics and Evolution 249, 67–76. Punt, W., Blackmore, S., Nilsson, S., Le Thomas, A., 1994. Glossary of pollen and spore terminology. LPP Foundation, Utrecht. Reeves, R.D., Brooks, R.R., Dudley, T.R., 1983. Uptake of nickel by species of Alyssum, Bornmuellera, and other genera of the old world tribus Alysseae. Taxon 32, 184–192. Retief, E., Siebert, S.J., Van Wyk, A.E., 2008. A new species of Euclea (Ebenaceae) from ultramafic soils in Sekhukhuneland, South Africa, with notes on its ecology. Bothalia 38, 31–37. Siebert, S.J., Van Wyk, A.E., Bredenkamp, G.J., 2001. Endemism in the flora of ultramafic areas of Sekhukhuneland, South Africa. South African Journal of Science 97, 529–532. Siebert, S.J., Van Wyk, A.E., Bredenkamp, G.J., 2002. The physical environment and major vegetation units of the Sekhukhuneland Centre of Plant Endemism, South Africa. South African Journal of Botany 68, 127–142. Van Wyk, A.E., Smith, G.F., 2001. Regions of floristic endemism in southern Africa. Umdaus Press, Hatfield. Venter, H.J.T., Winter, P.J.D., Verhoeven, R.L., Archer, R.H., 2007. Raphionacme villicorona (Apocynaceae: Periplocoideae), a new species from the Sekhukhuneland Centre of Plant Endemism, South Africa. South African Journal of Botany 73, 97–101. Vosa, C.G., 2007. Prototulbaghia, a new genus of the Alliaceae family from the Leolo Mountains in Sekhukhuneland, South Africa. Caryologia 60, 273–278. Wild, H., 1965. The flora of the Great Dyke of Southern Rhodesia with special reference to the serpentine soils. Kirkia 5, 49–86. Williamson, S.D., Robinson, E.R., Balkwill, K., 1997. Evolution of two serpentine endemic taxa in Mpumalanga. South African Journal of Botany 63, 507–513. Yang, X.-E., Jin, X.-F., Feng, Y., Islam, E., 2005. Molecular mechanisms and genetic basis of heavy metal tolerance/hyperaccumulation in plants. Journal of Integrative Plant Biology 47, 1025–1035.