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(cont.)
Thrixspermum is an orchid genus of about 150 species distributed from Sri Lanka and the Himalayan region, throughout Southeast Asia to the Southwest Pacific islands.1 Sumatra appears to represent the centre of diversity for the genus, with 38 species recorded.2 All species are either epiphytes or lithophytes, typically occurring in sunny, disturbed situations close to the coast, from sea level to around 1,500 m.
Thirteen species of Thrixspermum are currently known from China.3 One, T. amplexicaule, is known only from the eastern seaboard of Hainan Island, although it also occurs throughout mainland Southeast Asia, the Malay Archipelago, New Guinea and the Solomon Islands. Despite this wide distribution, surprisingly little is known about its ecology.
Herbarium material from across the species' range indicates that T. amplexicaule tends to occur in open, sunny sites prone to intermittent disturbance. In Hainan, it is found only in dry thorn-shrub thickets on volcanic rock around Haikou. The plant scrambles over low vegetation, sending out one aerial root at each node along its flat, slender stem. The leaves are narrowly ovate, clasping the stem at their base, and are arranged in two opposite rows. The plant produces long, erect racemes bearing several large pale pink to lilac flowers that flower in succession.
Though a plant may remain in flower for a few weeks, each individual flower only lasts one day or less. When the habitat becomes shaded by more substantial, woody vegetation,
T. amplexicaule becomes sterile, and may disappear altogether.
It is not known why individual flowers last for such a short period, and there are presently no data available on the species' pollinator, though it is presumed to be a medium-large insect.4
T. amplexicaule seems to thrive in a temporary niche typical of early-succession vegetation types. The species may become locally abundant, and in Hainan tens of plants have been observed in an area no greater than 1 m2. However, all of the known localities of T. amplexicaule in Hainan are situated outside the island's nature reserves. With the development of Haikou city, the volcanic rock areas upon which this species is dependent are facing increasing development pressure from tourism, urban expansion and golf courses. The species is listed as Vulnerable in China.5
(by Stephan Gale and Lu Gang)
References :
| 1 |
Govaerts R, Dransfield J, Zona SF et al., 2009. World Checklist of Arecaceae. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the Internet; http://www.kew.org/wcsp/accessed 24 March 2009. |
| 2 |
Comber, J. 2001. Orchids of Sumatra. Kew Publishing, UK. |
| 3 |
Chen S-C, Zhu G, Tsi Z et al., in press. Flora of China Volume 25 Orchidaceae. Science Press, Beijing, China & Missouri Botanical Garden Press, St Louis, USA. |
| 4 |
O'Byrne P, United World College of S.E. Asia, Singapore, personal communication. |
| 5 |
Chen YS and Chen XQ, 2004. Orchidaceae. In Wang S and Xie Y (eds.), China Species Red List, Higher Education Education Press. |
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