in Freyc., Voy. Uranie, Bot. (1826) 422, t. 33.
Sympodial epiphytes. Rhizome very short to much elongated. Pseudobulbs present, consisting of one internode, often slender (see Notes below), resembling a petiole, sometimes sharply 4-angled to 4-winged, 1-leaved. Leaves without sheathing base, glabrous, dorso-ventrally flattened, articulate, duplicate, leathery, often rather thick. Inflorescences terminal or subterminal, carrying a single flower. Flowers small to medium-sized, resupinate, often white, in section Cadetia apparently sometimes short-lived, otherwise lasting at least several days. Lateral sepals connate at the base, forming a mentum. Petals free, usually much narrower than the sepals. Lip adnate to the column-foot, without spur, not mobile, sometimes on the midlobe with low keels. Column pubescent in front below the stigma; column-foot present. Pollinia 4, solid-waxy, caudicles absent, stipe absent, viscidium absent. Ovary glabrous or with soft spine-like hairs or papillae, when glabrous usually 2- to 6-winged.
Java, Lesser Sunda Islands, Borneo, the Philippines, Sulawesi, Moluccas, New Guinea, Australia, east to Fiji. About 50 species; in New Guinea c. 45 species.
Epiphytes in lowland and montane forest, rarely terrestrial in steep mossy banks, or lithophytic on rocks and cliffs.
Whether regarded as a section of a very broadly circumscribed genus Dendrobium or as a genus in its own right, there can be no doubt that Cadetia forms a very distinctive and natural group of species. They are small plants with one-leaved slender stems or small swollen pseudobulbs. The short, one-flowered inflorescences arise from the apex of the stem in the axil of the leaf. In section Sarcocadetia an additional inflorescence arises from a point just below the apex of the stem on the abaxial side of the leaf. Most species have pure white flowers, including the not very aptly named C. citrina (Ridl.) Schuit., which has the largest flowers in the genus, up to 2.5 cm across. In cultivation only the Australian C. taylorii (section Cadetia; wrongly included in section Pterocadetia by Morris et al.) is fairly widespread in amateur collections, but the New Guinea taxa are not less worthy of attention by the lover of miniature orchids. Cadetias are generally easily cultivated, but they dislike being constantly wet at the roots, while on the other hand they should not be allowed to dry out too much. Species occurring at very high elevations, above 2500 m, have proved to be rather more difficult to keep in cultivation.
The genus can be divided into three sections, based on the position of the inflorescences and the shape of the cross-section of ovary and stem:
Inflorescences arising only from the leaf-axil, their base enveloped by a persistent, folded scale-leaf ('spathe'); ovary round in cross-section, usually densely covered with papillae or soft spine-like hairs; stems almost round to weakly 4-angled in cross-section, with rounded angles.
Inflorescences arising only from the leaf-axil, their base enveloped by a spathe; ovary triangular to almost V-shaped in cross-section or 6-ribbed, glabrous; stems usually sharply 4-angled in cross-section, with concave sides, often almost 4-winged.
Inflorescences arising from the leaf-axil and also from a point just below the stem apex on the abaxial side of the leaf, their base enveloped in a scarious tubular sheath and only in some species in addition by a spathe; ovary 6-winged to triangular to almost V-shaped in cross-section, glabrous; stems almost round to weakly 4-angled in cross-section, with rounded angles.
While the names of the two last-mentioned sections were originally proposed by Schlechter (1911-1914), the circumscription of the sections is modified here. As a result, many species included by Schlechter in section Pterocadetia (e.g. Cadetia chionantha) are now assigned to section Sarcocadetia. This somewhat unfortunate situation is a consequence of the typification of the sections by van Royen (1979).