Oeonia Lindl., Orchid. Scelet.: 14 (1826).
Heterotypic Synonyms:
Epidorkis Thouars, Nouv. Bull. Sci. Soc. Philom. Paris 1: 318 (1809).
Epidorchis Thouars, Hist. Orchid.: t. 81 (1822), orth. var.
Aeonia Lindl., Bot. Reg. 10: t. 817 (1824), orth. var.
Perrieriella Schltr., Repert. Spec. Nov. Regni Veg. Beih. 33: 365 (1925).
Description:
Epiphytic plants with slender, branched, woody stems and numerous adventitious roots. Leaves coriaceous, distichous, ovate, obovate or oblong. Inflorescences single or few-flowered, longer than the leaves; floral bracts short, tubular, sheath-ing the rachis. Flowers small to medium- sized; lip white or yellowish-white, sometimes spotted with red at the base; sepals and petals white, green or yellow-green.
Sepals elliptic, obovate or oblong, more or less spreading. Petals sub similar. Lip spreading, 3-6-lobed, the two basal lobes rounded, erect, clasping the column; spur continuous from the base of the lip, short, cylindrical or slightly inflated. Column short, erect, fleshy, without a foot, with two more or less rectangular lateral auricles; median tooth of rostellum distinct; anther incised in front, bilobed or broadly emarginate; pollinia 2, ovoid, borne on separate pollinaria, each with an oval stipe set below the rostellum, bearing the viscidium and a small, triangular caudicle attached to the pollinium and attached laterally to the stipe.
Distribution:
Oeonia is endemic to Madagascar and the Mascarene Islands. Bosser (1989) mentions four species and one variety in Oeonia : O. brauniana, O. brauniana var.sarcantboides, O. madagascariensis, O.rosea and O. volucris. In 2000, Bosser described a fifth species, which he called O. curvata (Bosser, 2000). All five species occur in Madagascar, with O. rosea also found in Reunion and O. volucris in Reunion and Mauritius (Du Puy et al.,1999).
Notes:
This small genus was first described at the same time as Cryptopus, in 1824, though it was misspell as Aeonia. Two years later, in his Collectanea Botanica, Lindley changed the spelling to Oeonia, from the Greek oionos, a bird of prey, presumably a reference to the flowers that have a fanciful resemblance to a bird in flight. Oeonia volucris was listed as an Epidendrum by Thouars when he discovered and illustrated it in 1822.
Cultivation:
In the wild, Oeonia is found in a range of habitats. Most species grow in mid-altitude forest (O. curvata, O. madagascariensis,O. rosea and O. volucris). O. brauniana grows at lower altitudes, where it is hotter and more humid. As explained by J. and C. Hermans (1994), Oeonia species are twig epiphytes, growing in the centre of their host trees. They form miniature climbers, which become attached to branches by their roots. Oeonia species are usually grown or mounted, but they also grow well in pots. However, their roots tend to be intolerant of the usual composts. For pot culture, chose a mixture of pellets of clay or lava rock and coarse bark.. The Hermans (1997) advise a mixture of sphagnum moss and Mexifem fibre. It is essential to use a compost that retains, moisture but does not become waterlogged.
Most species grow well mounted on a slab of cork or fern, where the aerial roots are not constrained - the stems and roots must be allowed to grow as they want. The addition of same coconut fibre to thee, mixture seems to help root development. For O. rosea (O. oncidiijlora), F. Hillerman (1979) advises attaching the plants to a slab of tree fem and winding it round the slab when the stems are long enough. Let the roots grow freely and avoid breaking or bruising them - when they reach their support, they will attach themselves.
Temperature, humidity and shaded:
Oeonia species are usually grown at intermediate temperatures: 18-25°C in summer and 18-20C in winter du ring the day and 15-18°C in summer and 12-15°C in winter at night. O. brauniana grows better in a warm glasshouse. Oeonia species can withstand temperatures over 25°C, but in that case, the humidity should be kept around 80%. Mist the plants twice daily if necessary and make sure the roots are kept moist. In winter, the frequency of misting depends on temperature, but one average, plants should be misted about, once every two days. Oeonia species require moderate shade, like most species of Aerangis. They grow at the edge of humid forests, usually in mid-canopy. In summer, 50% shade is necessary, but in winter, shading is only needed in very sunny areas.
Watering, fertilizing, ventilation:
Plants should be watered copiously in spring and summer, preferably in the morning. In winter, they should only be sprinkled, as early as possible in the day. However, they should not be allowed to dry out - the leaves should always be firm to the touch. The humidity needs to be monitored in both summer and winter. Good ventilation and air circulation is essential all year round, to avoid fungal infection. Fertilizers should only be applied while plants are actively growing.
Species:

World Checklist of Selected Plant Families.. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the Internet; http://www.kew.org/wcsp/ accessed 09/03/2017
Bibliography and References:
Bosser J. 1984 Contribution a l'etude des Orchidaceae de Madagascar et des Mascareignes: 21. (Contribution to the study of the Orchidaceae of Madagascar and the Mascarene Islands: 21.) Bull. Mus. Nation. Hist. Nat., B, Adansonia, 6. (3): 369-372 (1984)
Bosser J. 1989 Contribution a l'etude des Orchidaceae de Madagascar et des Mascareignes: 26. (Contribution to the study of the orchids of Madagascar and the Mascarenes: 26.) Bull. Mus. Nation. Hist. Nat., B, Adansonia 11. (4): 369-382 (1989)
Bosser J. 1989 Contributions a l'etude des Orchidaceae de Madagascar et des Mascareignes: 25. (Contribution to the study of the orchids of Madagascar and the Mascarenes: 25.) Bull. Mus. Nation. Hist. Nat., B, Adansonia 11. (2): 157-165 (1989)
Bosser J. 2000 Contribution a l'etude des Orchidaceae de Madagascar et des Mascareignes: 30. Description d'une nouvelle espece d' Oeonia de Madagascar. (Contribution to the study of *Orchidaceae from Madagascar and the Mascarenes: 30. Description of a new species of Oeonia from Madagascar.) Adansonia 22. (2): 231-233 (2000)
Carlsward BS, Stern WL, Bytebier B. 2006 Comparative vegetative anatomy and systematics of the angraecoids (Vandeae, Orchidaceae) with an emphasis on the leafless habit. Bot. J. Linn. Soc. 151. 165-218.
Cavestro W. 2004 Oeonia rosea Ridl.: une remarquable espece de Madagascar et de La Reunion. Orchidees Cult. Protect. 57. (1): 17-19 (2004)
Cavestro W. 2004 Oeonia, Cryptopus and Neobathiea: three angraecoid genera. 1. The genus Oeonia Lindl. Orchid Rev. 112. (1258): 219-226, 229 (2004)
Cavestro W. 2005 Oeonia, Cryptopus and Neobathiea: three angraecoid genera. Part 3. The genus Neobathiea Schltr. Orchid Rev. 113. 34-38
Hermans J, Hermans C. 1994 Scrambling in Madagascar: the genus Oeonia. Orchid Rev. 102. (1199): 268-271 (1994)
Hermans J, Hermans C. 1997 Oeonia: a unique genus from Madagascar. Orchids 66. (10): 1050-1054 (1997)
Herndon CN. 1997 Colorful Angraecoids Amer. Orchid Soc. Bull. Aug., 816-823.
Hillerman F. 1979 New and pleasant surprises from Madagascar. Amer. Orchid Soc. Bull. 48. (4): 335 - 340 (1979)