Burretiodendron Rehder (Malvaceae s.l.) is a genus of only six species, all of which are rare trees found only in tropical East Asia. Burretiodendron primarily grows in montane rain forests or dry deciduous forests. Both B. hsienmu and B. esquirolii are presently classified as vulnerable on the International Union for Conservation of Nature Red List. At present, there are no known pollen, wood, or fruit fossils of the genus Burretiodendron and little is known about its evolutionary history.
Prof. ZHOU Zhekun and his team of Xishuangbanna Tropical Botanical Garden (XTBG) discovered well-preserved fossil leaves and fruits dating from the Miocene (about 15-16 million years ago) in Yunnan close to the Vietnam border. Nine fossil fruits and four fossil leaves of Burretiodendron were recognized from their collection of approximately 5000 fossil specimens from Maguan and Wenshan. They proceeded with a detailed study of their macro and micro morphology and described two new species.
The researchers compared the fossil species with the six extant Burretiodendron species and identified their nearest leaving relatives. However, both fossil species are readily distinguished from extant species by their sizes, which are twice smaller while maintaining the same ratio of length to width.
From the presence of these fossils and the climatic requirements of modern Burretiodendron, the researchers inferred that the locality experienced frost free-winters and seasonal precipitations with wet summers and relatively dry winters. Their finding also supported the hypothesis that this genus might have originated at the Sino-Vietnam border, where its biodiversity is the highest today. It therefore reinforced the suggestion that the best location for in situ conservation of this genus lies at the Sino-Vietnamese border.
The study entitled “First Fruits and Leaves of Burretiodendron s.l. (Malvaceae s.l.) in Southeast Asia: Implications for Taxonomy, Biogeography and Paleoclimate” has been published in the International Journal of Plant Sciences.
Key words
Burretiodendron, Malvaceae, Miocene, East Asia, China, limestone flora
Contact
ZHOU Zhekun, Ph.D. Principal Investigator
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China
Tel: 86 691 8716932
Fax: 86 691 8715070
E-mail: zhouzk@xtbg.ac.cn
