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Flowering control of Ixodia achillaeoides
SCIENTIA HORTlCUlTURR Scientia Horticulturae 65 (1996) 59-64
Flowering control of Ixodia achillaeoides David Weiss *, Osnat Ohana The Kennedy Leigh Centre forHorticultural Research, The Hebrew University of Jerusalem, P.O. Box 12, Rehooor 76100, Israel
Accepted 14 September 1995
Abstract Ixodiu achillaeoides, a native be used in floral arrangements. flowering (< 17°C). Long days However, under these conditions,
of south Australia, is a potentially excellent cut flower that can The plant was found to require relatively low temperatures for reduced the time to flower initiation and sped up development. flower initiation occurred only on terminal shoots, while axillary shoots did not develop and remained vegetative. Under both natural short days kuting from October) and controlled short days, flowering time was delayed, but both lateral and terminal shoots developed and bloomed and thus many more flowers were formed. Growing ixodia plants first under short days and then under long days decreased time to flowering but reduced the number of flowers as compared with continuous short days. When plants were first grown under long days and then under short days, flower initiation occurred earlier (as compared with continuous short days), but not anthesis. The number of flowers formed with this treatment was similar to that found under continuous short days. Keywords: Apical dominance; Ixodia achillaeoides; Flowering; Photoperiod; Temperature regime
1. Introduction Ixodia (Zxodia achillaeoides, Asteraceae), a native of South Australia, is a shrub with dark green sticky leaves and a white papery everlasting capitulum (Wrigly and Fagg, 1978). I. achillaeoides, known also as mountain daisy, has always been regarded as a variable species but recent revision has recognized three subspecies, including ssp. alum. I. achillaeoide ssp. alata is 1 m high with flower heads varying in size from 5 to 15 mm in diameter. The ray flowers are white and the central disc can be either yellow,
* Corresponding author. Abbreviations: LD, long day; ND, natural day; PPPD, photosynthetic photon flux density; SD, short day. 0304-4238/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 0304.4238(95)00851-9
60
D. Weiss. 0. Ohana / Scieniia Horridwoe
65 (I 996) 59-64
lemon, white or mauve. Heads are held in clusters on short stalks at the end of branchlets. I. achillueoides is an excellent cut flower, suitable for drying, and often used in floral arrangements (Schaumann et al., 1987). Ixodia has been introduced as a new cut flower in Israel. Preliminary studies indicated that natural flowering occurred in late spring/early summer (April to June). We are unaware of any scientific publications on the physiology of ixodia flowering and there is, as yet, no available information on its responses to photoperiod or temperature. Because our preliminary experiments suggested that ixodia has potential as a cut flower, we studied its responses to different combinations of photoperiod and temperature.
2. Materials and methods
2.1. Plant material I. achillueoides ssp. alara was used in all experiments. Ixodia plants were produced locally from cuttings (taken from one plant) and two sets of experimental conditions were established: controlled conditions in the phytotron and ambient-temperature conditions in a net-house (10% shade). 2.2. Net-house
experiments
Experiments were carried out over 2 years (1993/ 1994 and 1994/ 1995). Rooted cuttings were planted in early October in 15cm pots containing 50% volcanic Scotia and 50% peat, or in ground beds, in a saran net-house providing 10% shade, under ambient temperature conditions. Plants grew under natural days (ND) or long days (LD, natural daylight plus light from incandescent lamps given throughout the night at a photosynthetic photon flux density (PPF’D) of 5-10 pmol me2 s- ‘J. 2.3. Phytotron experiments
Rooted cuttings were planted individually in 15-cm pots containing 50% volcanic scoria and 50% peat. Ten days later the plants were moved from the greenhouse to the phytotron (Ofir and Keller, 19741, where they were divided into eight lots of five plants each. Four night/day temperature regimes were selected: 27/32, 22/27, 17/22 and 12/ 17°C. For each temperature regime there were two photoperiodic treatments: LD and short day (SD). For LD conditions, the photoperiod was lengthened to 16 h by adding light from incandescent lamps at a PPFD of 5.3 pmol m-* s-‘. from before dawn to after sunset. For SD conditions (8-h photoperiod), plants were placed from 16:00 to 08:Ofl in adjacent dark rooms under the same conditions of temperature and relative humidity.
D. Weiss. 0. Ohana / S&da
Table
Hmriculrurue
65 (I 996) 59-64
61
I
Effect of phoropetiod on growth and flowering
of ixodia
spring temperatures in a net-house. Values are means of Day length
, grown from early October I5 replicates * SE
under ambient winter and
Days from
Days from
Number of
planting to
planting to
flower heads
flowering
flower bud
anthesis of
per plant
stems km)
appearance
first flower
ND
150*7
195*
10
750 f 39
102*5
LD
90&5
150*
9
69+
Length of
13
%?5
3. Results To study the effect of day length on growth and flowering, ixodia was planted in a net-house in early October under ND or LD conditions. The results summarized in Table 1 show that all plants bloomed under both ND and LD conditions. LD hastened flower initiation and anthesis by about 7 weeks, but reduced the number of flower heads per plant. Under LD conditions only terminal inflorescence clusters were formed, whereas under ND many lateral branches developed and formed flower heads. LD inhibited the development of axillary shoots and when they elongated (after senescence of the terminal flowers), they did not form flowers (data not shown). When plants were grown in the phytotron under different temperature regimes ( 17 to 32°C) and under LD or SD, flowering occurred only at the low temperature of 12/ 17°C (night/day) and only results from the two lower temperature regimes are therefore presented in Table 2. Plants kept at low temperatures, flowered earlier under LD and anthesis was observed 70 days before that in SD (Table 2). Under LD, the development of axillary shoots was inhibited and they remained vegetative, whereas under SD, both terminal and lateral shoots developed and initiated flower heads. Thus, the number of flower heads formed under SD conditions was much higher than under LD. Having established that low temperature was required for flower initiation, plants were first grown at the low temperature ( 12/ 17°C) under LD and then, after initiation of flowers (when flower buds were 2 mm long), half of the plants were transferred to LD at higher temperature (22/27”(Z). The rate of flower development was not affected by temperature
Table 2 Effect of photoperiod and temperature on flowering of ixodia. Plants were grown in controlled greenhouse chambers (phytotron). Values arc means of five replicates f SE Temperature (“C)
Day length
Days from
Days from
planting to
planting to
Number of flower heads
flower bud
anthesis
per plant
appearance l7/22 l2/17
nf, no flowers.
SD
nf
nf
0
LD
nf
nf
0
SD
175+7
203f8
325 k 56
LD
84k6
133k6
37*
I4
D. Weiss, 0. Ohana / Scientia Horticulrurae 65 (1996) 59-64
62
Table 3 Effect of photoperiod on growth and flowering of ixodia, grown under ambient winter and spring temperatures in a net-house. Plants were grown (starting at the end of October) under either ND; LD; 2 months ND followed by LD, or 2 months LD followed by ND. Values are means of 15 replicates k SE Day
length
ND LD ND to LD LD to ND
Days from
Days from
Numberof
planting to flower bud appearance
planting to anthesis
flower heads per plant
153,8 93+5 125+9 118k7
202* 11 147+ 7 164+ 10 204+ 12
825 + 85 76+ 9 245+21 812+73
and anthesis occurred at the same time at both low and high temperatures (data not shown). The above results indicate that LD shortens the time to flowering but reduces the number of flowers. To examine the possibility of shortening time to flowering without decreasing flower numbers, ixodia plants were exposed first to ND (SD in this experiment) and then to LD, and vice versa. Rooted cuttings were planted in pots and placed in a net-house in early October. The plants were divided into four treatment groups, consisting of ND; continuous LD; 2 months LD following by ND; and 2 months ND following by LD. The results again showed that LD reduces time to flowering, as well as number of flower heads (Table 3). Plants grown first under ND and then under LD, bloomed 1 month before plants grown under continuous ND and 1 month after plants grown under continuous LD. The number of flower heads formed by these plants was higher than that from continuous LD, but lower than that from continuous ND. Plants grown first under LD and then under ND initiated flowers 1 month before plants from continuous ND, but anthesis occurred at the same time, 45 days after plants from continuous LD. The number of flower heads in this treatment was similar to that found in plants grown in continuous ND.
4. Discussion Flowering in ixodia is promoted by low temperatures and affected by day length. Low temperature is an obligatory requirement for flowering and high temperatures (above 17°C) inhibited flower formation in both the phytotron (Table 2, Fig. 1) and the greenhouse (data not shown) under LD and SD. Low temperatures promote flowering of several other perennial Australian and South African plants such as Chamaelaucium uncinatum (Shill0 et al., 1985), Boronia megastigma (Roberts and Menary, 1989), Boronia serrulata (Lamont, 1989) and Coleonema aspalathoides (Heller et al., 1994). In Chamnelaucium uncinatum and Coleonema aspalathoides, SD enhances flower formation at low temperatures (Shill0 et al., 1985; Heller et al., 1994). The effect of day length on ixodia flowering was more complex. LD caused earlier flowering, but inhibited the number of initiated flowers. Under LD conditions, flowers were formed only on the leading terminal shoots, while the development of axillary shoots was
D. Weiss, 0. Ohana / Scientia Horticulturae
65 (1996) 59-64
63
Fig. I. Effects of different temperature regimes on flowering of ixodia. Plants were grown in the phytotron under SD at night/day temperatures of 17/22”C (right plant) or 12/17”C (left plant).
inhibited and they remained vegetative. Only after senescence of the terminal flowers, did axillary shoots start to elongate; even then however they did not flower (data not shown). The inhibition of flower formation on these shoots might have been caused by the high temperatures later in the season (May). SD delayed flowering of the terminal shoot but promoted lateral shoot elongation and when these plants were exposed to the inductive low temperature, both terminal and axillary shoots initiated flowers. Thus LD enhanced apical dominance and prevented flower formation on the inhibited axillary branches. The inhibitory effect of apical dominance on axillary shoot flowering has been found in many other plants including Impatiens, Hierucium (Kinet et al., 1985) and Euphorbia pulcherrima (Weiss, 1994). One of the main goals of this study was to find a way to shorten the time to flowering without reducing quality, as compared to ND-grown plants. Growing the plants under ND first (SD in October-November) and then under LD, reduced time to flowering but also reduced the number of flower heads (Table 3). The number of flowers that were initiated on plants that were first grown under LD and then under ND (starting with SD in December) was not reduced, and flower initiation occurred earlier; however, time to anthesis was delayed about the same as ND alone. These results may indicate that LD hastens not only flower initiation but also flower development. However, when plants were held continuously in one photoperiod, the time from flower bud appearance to anthesis was shorter under SD conditions (Table 2). Thus, in this case, SD hastened
64
D. Weiss, 0. Ohana / Scientia Horticuliurae 65 (I 996) 59-64
flower development. The reasons for these similar effects of apparently different daylength conditions are not clear. Growing the plants first under LD, to promote flower induction, then under SD to enhance axillary shoot elongation and finally under LD again, to promote flower development, may shorten time to flowering without reducing the number of initiated flowers. Decapitating the plants under LD conditions (and low temperatures) might lead to similar results. These and other treatments are to be tested next winter.
Acknowledgements The authors wish to thank Ms. Ofra Ziv for her technical assistance and Prof A.H. Halevy for his valuable comments and suggestions.
References Heller, A., Borochov, A. and Halevy, A.H., 1994. Factors affecting the growth and flowering of Coleonemn aspalathoides. Sci. Hortic., 58: 325-334. Kinet, J.M., Sachs, R.M. and Bemier, G., 1985. The Physiology of Flowering. Vol. III, CRC Press, Boca Raton, FL, 274 pp. Lamont, G.P., 1989. Boronia. In: A.H. Halevy (Editor), Handbook of Flowering. Vol. VI, CRC Press, Boca Raton, FL, pp. 117-121. Otir, M. and Keller, D., 1974. Relationship between thermoinduction and photoinduction of flowering and dormancy in Hordeum bulbosum L., a perennial grass. Aust. J. Plant Physiol., 1: 259-270. Roberts, N.J. and Menary, R.C., 1989. Environmental interaction between daylength, night temperature, and photon flux density on growth and flowering in Boroniu megasrigma Nees. J. Hort. Sci., 64: 597-604. Schaumann, M., Baker, J. and Greig, J., 1987. Australian Daisies. Lothian Publishing Company, Melbourne, 223 pp. Shillo, R., Weiner, A. and Halevy, A.H., 1985. Environmental and chemical control of growth and flowering of Chumaelaucium uncinurum Schaver. Sci. Hort., 25: 287-297. Weiss, D., 1994. Partial floral development in poinsettia. Flowering Newsl., 17: 44-48. Wrigly, J.W. and Fagg, M., 1978. Australian Native Plants. Collins Publishers, Sydney, 448 pp.
Flowering control of Ixodia achillaeoides David Weiss *, Osnat Ohana The Kennedy Leigh Centre forHorticultural Research, The Hebrew University of Jerusalem, P.O. Box 12, Rehooor 76100, Israel
Accepted 14 September 1995
Abstract Ixodiu achillaeoides, a native be used in floral arrangements. flowering (< 17°C). Long days However, under these conditions,
of south Australia, is a potentially excellent cut flower that can The plant was found to require relatively low temperatures for reduced the time to flower initiation and sped up development. flower initiation occurred only on terminal shoots, while axillary shoots did not develop and remained vegetative. Under both natural short days kuting from October) and controlled short days, flowering time was delayed, but both lateral and terminal shoots developed and bloomed and thus many more flowers were formed. Growing ixodia plants first under short days and then under long days decreased time to flowering but reduced the number of flowers as compared with continuous short days. When plants were first grown under long days and then under short days, flower initiation occurred earlier (as compared with continuous short days), but not anthesis. The number of flowers formed with this treatment was similar to that found under continuous short days. Keywords: Apical dominance; Ixodia achillaeoides; Flowering; Photoperiod; Temperature regime
1. Introduction Ixodia (Zxodia achillaeoides, Asteraceae), a native of South Australia, is a shrub with dark green sticky leaves and a white papery everlasting capitulum (Wrigly and Fagg, 1978). I. achillaeoides, known also as mountain daisy, has always been regarded as a variable species but recent revision has recognized three subspecies, including ssp. alum. I. achillaeoide ssp. alata is 1 m high with flower heads varying in size from 5 to 15 mm in diameter. The ray flowers are white and the central disc can be either yellow,
* Corresponding author. Abbreviations: LD, long day; ND, natural day; PPPD, photosynthetic photon flux density; SD, short day. 0304-4238/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved SSDI 0304.4238(95)00851-9
60
D. Weiss. 0. Ohana / Scieniia Horridwoe
65 (I 996) 59-64
lemon, white or mauve. Heads are held in clusters on short stalks at the end of branchlets. I. achillueoides is an excellent cut flower, suitable for drying, and often used in floral arrangements (Schaumann et al., 1987). Ixodia has been introduced as a new cut flower in Israel. Preliminary studies indicated that natural flowering occurred in late spring/early summer (April to June). We are unaware of any scientific publications on the physiology of ixodia flowering and there is, as yet, no available information on its responses to photoperiod or temperature. Because our preliminary experiments suggested that ixodia has potential as a cut flower, we studied its responses to different combinations of photoperiod and temperature.
2. Materials and methods
2.1. Plant material I. achillueoides ssp. alara was used in all experiments. Ixodia plants were produced locally from cuttings (taken from one plant) and two sets of experimental conditions were established: controlled conditions in the phytotron and ambient-temperature conditions in a net-house (10% shade). 2.2. Net-house
experiments
Experiments were carried out over 2 years (1993/ 1994 and 1994/ 1995). Rooted cuttings were planted in early October in 15cm pots containing 50% volcanic Scotia and 50% peat, or in ground beds, in a saran net-house providing 10% shade, under ambient temperature conditions. Plants grew under natural days (ND) or long days (LD, natural daylight plus light from incandescent lamps given throughout the night at a photosynthetic photon flux density (PPF’D) of 5-10 pmol me2 s- ‘J. 2.3. Phytotron experiments
Rooted cuttings were planted individually in 15-cm pots containing 50% volcanic scoria and 50% peat. Ten days later the plants were moved from the greenhouse to the phytotron (Ofir and Keller, 19741, where they were divided into eight lots of five plants each. Four night/day temperature regimes were selected: 27/32, 22/27, 17/22 and 12/ 17°C. For each temperature regime there were two photoperiodic treatments: LD and short day (SD). For LD conditions, the photoperiod was lengthened to 16 h by adding light from incandescent lamps at a PPFD of 5.3 pmol m-* s-‘. from before dawn to after sunset. For SD conditions (8-h photoperiod), plants were placed from 16:00 to 08:Ofl in adjacent dark rooms under the same conditions of temperature and relative humidity.
D. Weiss. 0. Ohana / S&da
Table
Hmriculrurue
65 (I 996) 59-64
61
I
Effect of phoropetiod on growth and flowering
of ixodia
spring temperatures in a net-house. Values are means of Day length
, grown from early October I5 replicates * SE
under ambient winter and
Days from
Days from
Number of
planting to
planting to
flower heads
flowering
flower bud
anthesis of
per plant
stems km)
appearance
first flower
ND
150*7
195*
10
750 f 39
102*5
LD
90&5
150*
9
69+
Length of
13
%?5
3. Results To study the effect of day length on growth and flowering, ixodia was planted in a net-house in early October under ND or LD conditions. The results summarized in Table 1 show that all plants bloomed under both ND and LD conditions. LD hastened flower initiation and anthesis by about 7 weeks, but reduced the number of flower heads per plant. Under LD conditions only terminal inflorescence clusters were formed, whereas under ND many lateral branches developed and formed flower heads. LD inhibited the development of axillary shoots and when they elongated (after senescence of the terminal flowers), they did not form flowers (data not shown). When plants were grown in the phytotron under different temperature regimes ( 17 to 32°C) and under LD or SD, flowering occurred only at the low temperature of 12/ 17°C (night/day) and only results from the two lower temperature regimes are therefore presented in Table 2. Plants kept at low temperatures, flowered earlier under LD and anthesis was observed 70 days before that in SD (Table 2). Under LD, the development of axillary shoots was inhibited and they remained vegetative, whereas under SD, both terminal and lateral shoots developed and initiated flower heads. Thus, the number of flower heads formed under SD conditions was much higher than under LD. Having established that low temperature was required for flower initiation, plants were first grown at the low temperature ( 12/ 17°C) under LD and then, after initiation of flowers (when flower buds were 2 mm long), half of the plants were transferred to LD at higher temperature (22/27”(Z). The rate of flower development was not affected by temperature
Table 2 Effect of photoperiod and temperature on flowering of ixodia. Plants were grown in controlled greenhouse chambers (phytotron). Values arc means of five replicates f SE Temperature (“C)
Day length
Days from
Days from
planting to
planting to
Number of flower heads
flower bud
anthesis
per plant
appearance l7/22 l2/17
nf, no flowers.
SD
nf
nf
0
LD
nf
nf
0
SD
175+7
203f8
325 k 56
LD
84k6
133k6
37*
I4
D. Weiss, 0. Ohana / Scientia Horticulrurae 65 (1996) 59-64
62
Table 3 Effect of photoperiod on growth and flowering of ixodia, grown under ambient winter and spring temperatures in a net-house. Plants were grown (starting at the end of October) under either ND; LD; 2 months ND followed by LD, or 2 months LD followed by ND. Values are means of 15 replicates k SE Day
length
ND LD ND to LD LD to ND
Days from
Days from
Numberof
planting to flower bud appearance
planting to anthesis
flower heads per plant
153,8 93+5 125+9 118k7
202* 11 147+ 7 164+ 10 204+ 12
825 + 85 76+ 9 245+21 812+73
and anthesis occurred at the same time at both low and high temperatures (data not shown). The above results indicate that LD shortens the time to flowering but reduces the number of flowers. To examine the possibility of shortening time to flowering without decreasing flower numbers, ixodia plants were exposed first to ND (SD in this experiment) and then to LD, and vice versa. Rooted cuttings were planted in pots and placed in a net-house in early October. The plants were divided into four treatment groups, consisting of ND; continuous LD; 2 months LD following by ND; and 2 months ND following by LD. The results again showed that LD reduces time to flowering, as well as number of flower heads (Table 3). Plants grown first under ND and then under LD, bloomed 1 month before plants grown under continuous ND and 1 month after plants grown under continuous LD. The number of flower heads formed by these plants was higher than that from continuous LD, but lower than that from continuous ND. Plants grown first under LD and then under ND initiated flowers 1 month before plants from continuous ND, but anthesis occurred at the same time, 45 days after plants from continuous LD. The number of flower heads in this treatment was similar to that found in plants grown in continuous ND.
4. Discussion Flowering in ixodia is promoted by low temperatures and affected by day length. Low temperature is an obligatory requirement for flowering and high temperatures (above 17°C) inhibited flower formation in both the phytotron (Table 2, Fig. 1) and the greenhouse (data not shown) under LD and SD. Low temperatures promote flowering of several other perennial Australian and South African plants such as Chamaelaucium uncinatum (Shill0 et al., 1985), Boronia megastigma (Roberts and Menary, 1989), Boronia serrulata (Lamont, 1989) and Coleonema aspalathoides (Heller et al., 1994). In Chamnelaucium uncinatum and Coleonema aspalathoides, SD enhances flower formation at low temperatures (Shill0 et al., 1985; Heller et al., 1994). The effect of day length on ixodia flowering was more complex. LD caused earlier flowering, but inhibited the number of initiated flowers. Under LD conditions, flowers were formed only on the leading terminal shoots, while the development of axillary shoots was
D. Weiss, 0. Ohana / Scientia Horticulturae
65 (1996) 59-64
63
Fig. I. Effects of different temperature regimes on flowering of ixodia. Plants were grown in the phytotron under SD at night/day temperatures of 17/22”C (right plant) or 12/17”C (left plant).
inhibited and they remained vegetative. Only after senescence of the terminal flowers, did axillary shoots start to elongate; even then however they did not flower (data not shown). The inhibition of flower formation on these shoots might have been caused by the high temperatures later in the season (May). SD delayed flowering of the terminal shoot but promoted lateral shoot elongation and when these plants were exposed to the inductive low temperature, both terminal and axillary shoots initiated flowers. Thus LD enhanced apical dominance and prevented flower formation on the inhibited axillary branches. The inhibitory effect of apical dominance on axillary shoot flowering has been found in many other plants including Impatiens, Hierucium (Kinet et al., 1985) and Euphorbia pulcherrima (Weiss, 1994). One of the main goals of this study was to find a way to shorten the time to flowering without reducing quality, as compared to ND-grown plants. Growing the plants under ND first (SD in October-November) and then under LD, reduced time to flowering but also reduced the number of flower heads (Table 3). The number of flowers that were initiated on plants that were first grown under LD and then under ND (starting with SD in December) was not reduced, and flower initiation occurred earlier; however, time to anthesis was delayed about the same as ND alone. These results may indicate that LD hastens not only flower initiation but also flower development. However, when plants were held continuously in one photoperiod, the time from flower bud appearance to anthesis was shorter under SD conditions (Table 2). Thus, in this case, SD hastened
64
D. Weiss, 0. Ohana / Scientia Horticuliurae 65 (I 996) 59-64
flower development. The reasons for these similar effects of apparently different daylength conditions are not clear. Growing the plants first under LD, to promote flower induction, then under SD to enhance axillary shoot elongation and finally under LD again, to promote flower development, may shorten time to flowering without reducing the number of initiated flowers. Decapitating the plants under LD conditions (and low temperatures) might lead to similar results. These and other treatments are to be tested next winter.
Acknowledgements The authors wish to thank Ms. Ofra Ziv for her technical assistance and Prof A.H. Halevy for his valuable comments and suggestions.
References Heller, A., Borochov, A. and Halevy, A.H., 1994. Factors affecting the growth and flowering of Coleonemn aspalathoides. Sci. Hortic., 58: 325-334. Kinet, J.M., Sachs, R.M. and Bemier, G., 1985. The Physiology of Flowering. Vol. III, CRC Press, Boca Raton, FL, 274 pp. Lamont, G.P., 1989. Boronia. In: A.H. Halevy (Editor), Handbook of Flowering. Vol. VI, CRC Press, Boca Raton, FL, pp. 117-121. Otir, M. and Keller, D., 1974. Relationship between thermoinduction and photoinduction of flowering and dormancy in Hordeum bulbosum L., a perennial grass. Aust. J. Plant Physiol., 1: 259-270. Roberts, N.J. and Menary, R.C., 1989. Environmental interaction between daylength, night temperature, and photon flux density on growth and flowering in Boroniu megasrigma Nees. J. Hort. Sci., 64: 597-604. Schaumann, M., Baker, J. and Greig, J., 1987. Australian Daisies. Lothian Publishing Company, Melbourne, 223 pp. Shillo, R., Weiner, A. and Halevy, A.H., 1985. Environmental and chemical control of growth and flowering of Chumaelaucium uncinurum Schaver. Sci. Hort., 25: 287-297. Weiss, D., 1994. Partial floral development in poinsettia. Flowering Newsl., 17: 44-48. Wrigly, J.W. and Fagg, M., 1978. Australian Native Plants. Collins Publishers, Sydney, 448 pp.