Included here are tropical parts of Laos, Vietnam, Cambodia and a small part of Thailand. The forests can be broadly divided into northern and southern types.

North Indochinese Acidic Evergreen Forest

These forests of acidic, silicate soils range from the lowlands to an altitude of about 1000 m. They are mostly are very wet and very closed, and the largest trees can reach heights of 50 m and have diameters of more than 2 m. Among the dominant canopy families are Fabaceae, Fagaceae, Lauraceae, Magnoliaceae and Myrtaceae, while common genera from other families include Acer (Aceraceae), Swintonia (Anacardiaceae), Anisophyllea (Anisophylleaceae), Alstonia (Apocynaceae), Canarium (Burseraceae), Calophyllum (Clusiaceae), Dipterocarpus (Dipterocarpaceae), Elaeocarpus (Elaeocarpaceae), Macaranga (Euphorbiaceae), Ixonanthes (Ixonanthaceae), Aglaia (Meliaceae), Artocarpus (Moraceae), Celtis (Ulmaceae), Sapindus (Sapindaceae), Scaphium (Sterculiaceae) and Schima (Theaceae). In the wetter conditions at altitudes above 600 m gymnosperms become a major component of the canopy with species such as Dacrycarpus imbricatus, Dacrydium elatum and Podocarpus neriifolius. Several other tree strata can often be distinguised ranging from 5-15 m. Common genera among these are Ilex (Aquifoliaceae), Garcinia (Clusiaceae), Elaeocarpus (Elaeocarpaceae), Baccaurea (Euphorbaceae), Lithocarpus (Fagaceae), Apodytes (Icacinaceae), Engelhardtia (Juglandaceae), Lindera (Lauraceae), Manglietia (Magnoliaceae), Chisocheton (Meliaceae), Horsfieldia (Myristicaceae), Cinnamonmum (Myrtaceae), Pygeum (Rosaceae), Meliosma (Sabiaceae), Mischocarpus (Sapindaceae), Symplocos (Symplocaceae), Pyrenaria (Theaceae) and Xanthophyllum (Xanthophyllaceae). Lianas like Ancistrocladus cochinchinensis and Pseudostachyum polymorphum are important together with strange orchid lianas like Arachnis annamensis, Callostylus rigida, Epigeneium ampilum, Renanthera annamensis, Staurochilus fasciatus, Thrixspermum centipeda and the remarkable leafless, achlorophyllous, mycotrophic Galeola nudifolia which can reach 10 m or so in length. Mention should also be made of the rattans. Species such as Calamus bousinggonii, C. pseudoscuttellaris and C. tetradactylus can be important particularly in the uplands.

The herb layer of these shady, humid forests is also surprisingly rich with orchids again being one of the most conspicuous groups. Some of the common orchids include Acanthephippium odoratum, Anoectochilus roxburghii, Calanthe lyroglossa, Cephalantheropsis longipes, Corymborkis veratrifolia, Cymbidium sinense, Geodorum densiflorum, Habenaria seshagiriana, Hetaeria pauciflora, Liparis nigra, Ludisia discolor, Malaxis octodentata, Paphiopedilum callosum, Phaius flavus, Tainia angustifolia and Tropidia curculigoides. Also at ground level are a number of the unusual achlorophyllous, mycotrophic orchids like Aphyllorchis annamensis, Didimoplexiopsis khiriwongensis, Epipogium roseum, Lecanorchis javanica and Stereosandra javanica. Not surprisingly the epiphytic flora of these humid forest is very rich with orchids again being one of the most important groups. In fact, more than half of all the orchids of these forests are epiphytes. Commonly occurring species include Acampe ochracea, Acriopsis indicam Aerides falcata, Agrostophyllum brevipes, Appendicula hexandra, Bulbophyllum affine, Ceratostylis radiata, Cleisostoma duplicilobum, Dendrobium amabile, Eparmatostigma dives, Eria acervata, Flickingeria forcipata, Gastrochilus intermedius, Liparis elliptica, Luisia pysche, Microptera poilanei, Ornithochilus difformis, Pholidota leveleana, Polystachya concreta, Pomatocalpa spicata, Pteroceras leopardinum, Robiquetia succisa, Sarcoglyphis mirabilis, Thecopus maingayi, Thecostele alata, Thrixspermum pauciflorum, Trias nasuta and Trichotosia dalatensis.

South Indochinese Evergreen Forest

Closed evergreen forest can be found, for example, in southern Vietnam where the high rainfall compensates for the short dry season. These are structurally complex with at least three vertical stories and have well-developed undergrowth of shrubs. The upper canopy can reach heights of up the 50 m and is typically dominated by dipterocarps such as Anisoptera cochinchinensis, Dipterocarpus alatus, D. costatus, D. dyeri, D. turbinatus, Shorea vulgaris and species Hopea. Other common trees include the endemic or near endemic Dalbergia cochinchinensis (Fabaceae) and Sindora cochinchinensis (Fabaceae). Apart from Dipterocarpaceae other common plant families are Ebenaceae, Fabaceae, Hypericaceae and Meliaceae.


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