Gen. Sp. Orchid. Pl. (1830) 63
Monopodial or sympodial plants, without, or with very short to long rhizomes. Stem very short or elongated. Pseudobulbs present or not, consisting of one to several internodes, when present 1- to few-leaved, when pseudobulbs absent stem few- to many-leaved. Leaves sheathing at the base, glabrous, rarely laterally compressed, deciduous, duplicate, rather thin-textured to leathery or carnose. Inflorescence lateral from the base of the pseudobulb, or lateral from the stem, a many-flowered raceme. Flowers small to very small, resupinate, white or greenish. Sepals free. Petals free, usually similar to the dorsal sepal, but somewhat smaller. Lip with or without spur, not mobile. Column-foot present. Pollinia 8, solid, caudicles present, stipe absent, viscidium present.
Northeast India, tropical East Asia, Malaysia, Indonesia, the Philippines, Papua New Guinea, Australia, New Zealand, Pacific islands, east to Tahiti. About 150 species; in New Guinea c. 100 species.
Epiphytic in evergreen lowland and montane forest.
A genus of rather inconspicuous plants, usually with dense racemes of many tiny white flowers, sometimes pleasantly fragrant. Phreatia is one of the few orchid genera where the vegetative parts are much more diverse than the flowers. It is related to Thelasis, but the more delicate flowers have a distinct column-foot and a short rostellum. In both genera we find species having well-developed, few-leaved pseudobulbs along a creeping rhizome, as well as species with only a few clustered stems with several to many leaves without rhizome or pseudobulbs. Identification of the species of Phreatia is often difficult since the flowers generally show few distinguishing characters. Schlechter proposed a division into sections that is partly based on floral characters and partly on vegetative ones. As in many other genera we have found his classification, even though it will probably not reflect the phylogeny of the genus, useful for identification purposes. We depart from his classification in that we refer his sections Diplostypus and Rhynchophreatia to the genus Thelasis (sect. Hemithelasis). We must also add that we have grave doubts if the distinction between sections Plexaure (short-stemmed plants without pseudobulbs) and Caulophreatia (long-stemmed plants without pseudobulbs) can be upheld. Species of Phreatia are rarely observed in cultivation and we can hardly foresee a future in which this will change to any great extent.
Key to the sections of Phreatia
1a Plant with pseudobulbs, often with distinct creeping rhizome ... 2
1b Plant without pseudobulbs, without rhizome ... 3
2a Lip with a basal sac or spur ... section Phreatia (synonym: section Saccophreatia)
2b Lip without a basal sac or spur ... section Bulbophreatia
3a Stem short, mainly formed by the overlapping leaf sheaths ... section Rhizophyllum (synonyms: sect. Plexaure, sect. Euphreatia)
3b stem elongated ... sect. Caulophreatia