Included here are tropical parts of Laos, Vietnam, Cambodia and a small part of Thailand.

North Indochinese Calcareous Lowland Evergreen Forest

The remaining remnants of these once extensive forests occur on a few plains and slopes of limestone plateaus and on the terraces of river valleys. Their closed canopies can reach heights of up to 35 m and are mainly dominated by representatives of typical tropical families. Characteristic genera include Choerospondias, Dracontomelon (Anacardiaceae), Garcinia (Clusiaceae), Anogeisus, Terminalia (Combretaceae), Tetrameles (Datiscaceae), Parashorea, Vatica (Dipterocarpaceae), Diospyros (Ebenaceae), Erythrophleum, Paralbizzia, Saraca (Fabaceae), Caryodaphnopsis, Cynnamomum, Phoebe (Lauraceae), Aglaia, Chisocheton (Meliaceae), Ficus, Streblus (Moraceae), Pometia (Sapindaceae), Madhuca (Sapotaceae), Canarium (Simaroubaceae), Pterospermum, Sterculia (Sterculiaceae), Rehderodendron (Styracaceae) and Burretiodendron (Tiliaceae). Other trees from less typically thermophilous families include Liquidamber formosana and Symingtonia tonkinensis and tropical oaks like Castanopsis indica, Lithocarpus bacgiangensis and L. licentii.

The ground flora of these base-rich forests is extremely rich and particularly well endowed with hygrophilous and skiophilous (shade tolerant) orchids. Examples include Calanthe alismifolia, Corymborkis eratrifolia, Cymbidium ensifolium, Erythrodes blumei, Geodorum attenuatum, Goodyera foliosa, Habenaria ciliolaris, Hetaeria rubens, Liparis nervosa, Malaxis acuminata, Nervilia fordii, Tropidia angulosa, Vrydagzynea albida, Zeuxine nervosa and the local endemic Zeuxine vietnamica (Orchidaceae). Also found in the ground flora are the primitive orchids Neuweidia griffithii and N. inae. The group that includes these (the Apostasioideae) is now thought to be ancestral to all remaining orchid groups. Other interesting ground layer species include a group of achlorophyllous, mycotrophic orchids (species without chlorophyll that rely on fungus for their nutrition). These include Cyrtosia javanica, Didimoplexiopsis khiriwongensis, Didimoplexis pallens, Epipogium roseum, Erythrorchis ochobiensis and the endemic Vietorchis aurea (Ochidaceae). The genus Vietorchis is endemic to this BioProvince. Equally rich is the epiphytic flora. These include lianas like the fleshy-stemmed Vanilla annomica that can reach lengths of 10 m. But orchids are again possibly the most conspicuous feature of the epiphytes with species such as Aerides odorata, Callostylis rigida, Ceratostylis himalaica, Cleisostoma aspersum, Coelogyne fimbriata, Cymbidium aloifolium, Dendrobium acinaciformis, Eria pannea, Liparis viridiflora, Malleola insectifera, Ornithochilus difformis, Pelatanthera insectifera, Phalaenopsis lobbii, Pholidota rubra, Robiquetia succisa, Thrixspermum centipeda, Trichotosia dasyphylla and the Vietnamese endemics Biermannia calcarata, Dendrobium nobile var. albolutea, Phalaenopsis gibbosa and Pteroceras simondianum (Orchidaceae).

References

Averyanov, L. V., Phan Ke Loc, Nguyen Tien Hiep, & Harder, D. K. 2003. Phytogeographic review of Vietnam and adjacent areas of Eastern Indochina. Komarovia, 3: 1-83.

Vidal, J. E. 1979. Outlines of the ecology and vegetation of the Indochinese Peninsula. In: Tropical Botany. Eds. K. Larsen and L. B. Holm-Nielsen. Academic Press.

Vidal, J. E. 1997. Paysages vegetaux et Plantes de la Peninsule indochinoise. Karthala and Agency of Francophony, Paris.

Walker, E. H. & Pendleton, R. L. 1953. A survey of the vegetation of southeastern Asia. The Indo-Chinese Province of the Pacific Basin. Proceedings of the 8th Pacific Science Congress, 4: 99-144.

Williams, L. 1965. Vegetation of Southeast Asia. Studies of Forest Types. 1963-1965. Agricultural Research Services. U.S. Department of Agriculture.