Rhipidoglossum Schltr., Beih. Bot. Centralbl. 36(2): 80 (1918).
Heterotypic Synonyms:
Crossangis Schltr., Beih. Bot. Centralbl. 36(2): 141 (1918).
Sarcorhynchus Schltr., Beih. Bot. Centralbl. 36(2): 104 (1918).
Plants with short or long stem, pendent or up-right, branched or not. Leaves coriaceous or fleshy, or thin-textured, unequally 2-lobed at the apex. Inflorescence emerging through the sheathing leaf-bases in the upper part of the stem. Flowers usually small to tiny, translucent. Sepals and petals dissimilar. Lip entire or obscurely 2-, 3- or 4-lobed, ecallose or with transverse or finger-like callus in the spur mouth. Spur prominent. Gynostemium erect, rather slender, distinctly swollen towards the base. Stigma elliptic, deeply concave. Anther incumbent, operculate, slightly elongate towards 1 the apex. Pollinia 2, ellipsoid, porate. Rostellum finger-like, fleshy, rather thick, acute. Viscidia ' double, more or less ovate-triangular, thin, delicate, lamellate. Tegulae double, linear, thin, deli cate, lamellate. Both viscidia and tegulae produced ( on both sides of the rostellum. Rostellum acute, finger-like after removal of pollinaria.
Trop. & S. Africa
Many of the white, pale green, or yellowish flowers of Rhipidoglossum species have a fan-shaped lip, and it was this feature which gave Rudolf Schlechter the idea for the generic name in 1918, from the Greek words rhipis, fan, and glossum, tongue. Schlechter proposed Rhipidoglossum as distinct from Diaphananthe and other African angraecoids because of the way the lip was attached to a short column foot in the 5 species that he recognised.
As the number of species described has grown, to a current total of nearly 40 in Rhipidoglossum and 25 in Diaphananthe, this feature has proved to be less easily observed, and some botanists have found it difficult to distinguish positively between the 2 genera. Summerhayes, in particular, found it so difficult that he proposed to amalgamate the 2I genera (1960). However, he treated Rhipidoglossum~ as a distinct section including all those species in which each of the 2 pollinia is attached by a short stalk to its own viscidium, whereas in Diaphananthe one viscidium is shared by 2 separate stipes.
Schlechter had not been so definitive about this feature. A callus or tooth on the lip, in the mouth of the spur, has sometimes been used as a distinguishing character for Diaphananthe, although it is not always present, but it is also present, to some degree, in some species of Rhipidoglossum. Garay,: (1972), Senghas (1986), and others have favoured treating the 2 genera separately.
Some plants of Rhipidoglossum species have a short stem with the flat leaves arranged in a neat rosette or fan, while others make untidy specimens in the wild, with straggling, branching stems that produce many elongated aerial roots. The roots are often the first part to catch the eye. The inflorescences are short or long and often produced in great numbers. The flowers are generally small, but when viewed close-up they are attractive and make distinguishing the species relatively easy by details of the lip and spur.
Sarcorhynchus was also established by Schlechter in 1918 for those species with a fleshy rostellum and4-lobed lip, but only 4 species have been assigned to it. These are currently included in Rhipidoglossum. Some species of Cribbia and Angraecopsis also have somewhat translucent flowers and a column with a 3-lobed rostellum, but they have not been confused with any in the genus Rhipidoglossum so far. Further investigation, especially the availability of DNA information, may provide the evidence needed for a new assessment of the generic limits in this group of orchids. In the folIowing account the species are presented in 2 groups, based on their habit:
Group l.
Stems short, usually less than 12 cm long, with leaves arranged in a rosette or fan, ar, in plants with longer stems, in 2 rows along the sides of the upper part of the stem.
Group 2.
Stems elongated, at least 20 cm long in mature plants, leafy along most of their length.
Notes two:
A revised concept of Rhipidoglossum (Angraecinae, Orchidaceae) was make May 2018 Phytotaxa 349(3) therefore new combinations in Diaphananthe, Rhipidoglossum, Cribbia, Rhaesteria, Margelliantha and one species from Angraecopsis, and one species from Mystacidium but without a key:
New species from old genus Margelliantha, Cribbia, Rhaesteria below:

Rhipidoglossum brachyceras (Summerh.) Farminhão & Stévart Trop. Africa 
Rhipidoglossum burttii (Summerh.) Summerh. E. DR Congo to W. Rwanda
Rhipidoglossum caffrum (Bolus) Farminhão & Stévart Limpopo to E. Cape Prov. 
Rhipidoglossum clavatum (P.J.Cribb) Farminhão & Stévart Tanzania (W. Usambara Mts.) 
Rhipidoglossum confusum (P.J.Cribb) Farminhão & Stévart W. & WC. Trop. Africa 
Rhipidoglossum eggelingii (Summerh.) Farminhão & Stévart SW. Uganda to Rwanda 
Rhipidoglossum globulare (P.J.Cribb) Farminhão & Stévart Tanzania (Uluguru Mts.) 
Rhipidoglossum leedalii (P.J.Cribb) Farminhão & Stévart SE. Kenya to Tanzania
Rhipidoglossum millarii (Bolus) Farminhão & Stévart SE. Cape Prov. to SW. KwaZulu-Natal
Rhipidoglossum pendulum (la Croix & P.J.Cribb) Farminhão & Stévart São Tomé 
Rhipidoglossum pusillum (Summerh.) Farminhão & Stévart   E. DR Congo 
Rhipidoglossum thomense (la Croix & P.J.Cribb) Farminhão & Stévart              São Tomé 

All these species can be grown in cultivation without difficulty, though most of them grow better when mounted on a piece of bark than when planted in a pot. Due regard should be paid to the altitudinal range of each species in the wild, as some will require much cooler night temperatures than others.
Bibliography and References:
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.
Johansson D. 1974 Rhipidoglossum paucifolium, a new African species of Orchidaceae. Bot. Notiser 127. (1): 149-151 (1974) Illustrations. Geog=5 (KR, 197403793).
Summerhayes V.S. 1937. Rhipidoglossum brevifolium, Catalogue of the vascular plants of S. Tomé. Blumea, Suppl. I. 83.
WCSP (2017). 'World Checklist of Selected Plant Families. 14.11.2020; http://apps.kew.org/wcsp/