Dendrobium orchids are found throughout the western Pacific and east Asia from as far north as Japan to as far south as Tasmania and southern New Zealand, east to Tahiti and west to western India (Lavarack et al. 2000). The genus (as currently delineated) includes more than a thousand species found in widely varying habitats (Lavarack et al. 2000; Adams et al. 2006). Like most other epiphytes, Dendrobium orchids are restricted to areas of moderate to high rainfall (e.g., in tropical lowlands, annual rainfall of more than 150 cm and a dry season of less than 6 months; at higher elevations in the tropics, or in cooler temperate regions, drier conditions can be tolerated). Dendrobium are found from just above the treeline on the highest mountains to the branches of trees overhanging the ocean. They are absent from some of the drier forests and woodlands, deserts and semi-deserts, and alpine and other cold environments. They are mainly inhabitants of primary forest, especially the rainforests of Southeast Asia and New Guinea. Swamp forests (such as those dominated by Melaleuca species) and mangrove forests may also support large numbers of individuals and species. Relatively few Dendrobium species are found in monsoonal forests and woodlands, but populations of species that do occur in these habitats can be dense. The small number of species found in the subalpine shrubbery of tropical mountains are of particular interest in that most of them have brightly colored flowers. Some species are well adapted to disturbed habitats. (Lavarack et al. 2000)
As a consequence of the fact that the genus includes many species that are generally compact, fabulously colorful, and often easy to grow, Dendrobium are among the most horticulturally important orchids. Given the great range of habitats and altitudes at which various species grow, some appropriate species can be found for cultivation in most climates. Although there are many rare and endangered species, Dendrobium are common in both the wild and in gardens in southern Asia; the Malesian Islands (i.e., the islands to the east of Southeast Asia, including New Guinea), the Pacific Islands (the islands south and east of the Solomon Islands, the endemic-rich New Caledonia being the largest of these), and Australia. New Guinea has the greatest diversity of Dendrobium, both in number of species and in diversity per unit area. Lavarack et al. review the historical biogeography of Dendrobium. (Lavarack et al. 2000)
Dendrobium orchids vary in size from tiny creeping plants less than a centimeter high (e.g., D. toressae) to clumped bamboo-like plants several meters tall (e.g., D. discolor). Although most are epiphytes, some grow on rocks or on the ground. All Dendrobium (even the terrestrial species) have coarse, spreading root systems, unlike the tuberous root systems characteristic of terrestrial orchids from temperate regions. (Lavarack et al. 2000)
Dendrobium orchids typically produce large numbers of very small and easily dispersed seeds. These seeds contain almost no food reserves. Seedlings must quickly form mycorrhizal associations with appropriate fungi to supply them with needed nutrition as they develop. (Lavarack et al. 2000)
Perhaps a third of the 30,000 or so orchid species are deceptive, attracting pollinators but then failing to reward them with pollen or nectar. Many of these orchids imitate the scent of rewarding flowers or potential mates. However, one rewardless Dendrobium orchid, Dendrobium sinense, is pollinated by the hornet Vespa bicolor, which it apparently attracts by mimicking the alarm pheromone produced by honeybees, which hornets frequently hunt as food for their larvae (Brodmann et al. 2009).
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