Study of the DNA for relationship of Anacardiaceae and Burseraceae families in Vietnam
Studying these two plant families in the field and making special collections for anatomical and phylogenetic research are helping to decipher their evolutionary and biogeographic histories; in turn, with an understanding of their patterns of diversity in this region, botanists can contribute to identifying areas of highest conservation priority and lend substantial weight to arguments for protecting the conservation units in which key taxa are found. The plan for the field work focused primarily on finding several genera occurring in Vietnam that had never been sampled for phylogenetic studies; many of them are poorly known and in urgent need of taxonomic revision. The expedition photographed all parts of each tree and collected herbarium samples; liquid-preserved flowers, fruits, and leaflets for developmental and anatomical studies; and silica-dried leaf samples for the molecular systematic work.
For the Anacardiaceae, the expedition found and collected some 25 species in 15 genera, including five genera whose DNA had never been sampled for the family phylogeny. Among the interesting trees the botanists collected in the Anacardiaceae were two species of Pentaspadon. This tropical Asian genus is distributed from Thailand south to the Solomon Islands, but only five species are known, and two of them, P. annamense and P. poilanei, are known only from Vietnam. The genus is interesting because on the underside of the leaflets in most of the species, at the points where the secondary veins branch from the primary vein, there are tiny cavities surrounded by tufts of hairs and inhabited by mites (Acari); these cavities are visible in the photo of P. motleyi. The fruits are also unusual in that they are relatively small (only up to 3 cm long in the Vietnamese species), fusiform (spindle-shaped) to narrowly ovoid (egg-shaped), and sparsely dotted with large raised spots called lenticels; the pulp around the stone is very resinous, and the seed within the stone is rich in oil. The fruits of some species are considered to be edible after boiling.
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| Habit and habitat of Pentaspadon poilanei on Tien Du Mountain, near Nha Trang City, Khanh Hoa Province | Fruit of Pentaspadon annamense, collected in Hon Ba Nature Reserve, Khanh Hoa Province |
Leaflet of P. motleyi, a relative of the Vietnamese species, showing the mite-inhabited domatia (see text).
Traditionally, Pentaspadon was considered to be related to the cashew (Anacardium) and the lacquer-tree genus Toxicodendron (son phutho) in the subfamily Anacardioideae, but analysis of the DNA material collected on the joint VAST-NYBG expedition showed that in fact Pentaspadon is more closely related to the fruit tree Spondias pinnata (coc rung) in the subfamily Spondioideae. Interestingly, this conclusion had been reached in 1990 by two previous researchers, Wannan and Quinn, based on similarities in the anatomy of the fruit.
The 46 collections of Burseraceae made during the 2010 expedition represented 4 genera and 14 species, compared with 5 genera and 20 species recorded in the most recent published flora of the whole country. The most notable Burseraceae was the mysterious “Bursera” tonkinensis, named by the French botanist André Guillaumin in 1907 and based on a collection from Ké So, near Phu-ly in Ha Nam. It is exceedingly rare, as only three collections were known, but the 2010 expedition was able to find a population of 2-3 small trees in the foothills of the northern Annamite Mountains, in Cuc Phuong National Park. Cuc Phuong is Vietnam’s first forest reserve, decreed in 1962 and made a national park in 1966; it consists of hilly areas of lowland forest punctuated by small but very steep karst (limestone) mountains, and it was on top of one of these mountains that the expedition found a population of B. tonkinensis.
As noted, Guillaumin placed this species in the Bursera, an otherwise New World genus of probably 120 species, most of them endemic to Mexico, where the genus dominates many of the country’s dry forests. The rest of the genus is found in Central America and the Caribbean, with six species in northern South America. The genus is very closely related to Commiphora, which is distributed in drier parts of Africa, Arabia, and southern Asia, with one species recognized in parts of Northeastern South America. Strangely, one recently discovered new species of Bursera, B. pereirae, is the first to be recorded from Central Brazil, and preliminary molecular analyses suggest that Bursera tonkinensis, B. pereirae, and a third species that is a large rainforest tree in far northeastern Colombia, B. inversa, are among the most basal (archaic) species in the clade or branch of Burseraceae that includes Bursera. In fact, B. tonkinense may prove to be sister to all the rest of the species in Bursera and it may possibly represent a distinct genus.
The results of the 2010 expedition greatly advanced our understanding of the Anacardiaceae and Burseraceae, and this highlights the importance of expanding the botanical inventory of Vietnam, which is essential not only for determining the evolutionary position and taxonomic assignment of numerous genera and species whose relationships are unknown, but also for creating a baseline of information about the flora that is robust enough for VAST-IEBR to help guide conservation policy.
Bursera tonkinensis_habitat1. Forest on steep slope of karst mountain in Cuc Phuong National Park
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| Bark and slash/blaze | Vein patterns of leaflet |
Translated by Dr. Douglas Daly, TS. John Mitchell và TS. Susan Pell (NYBG)
Dr. Nguyen The Cuong(IEBR)
