Holothrix species some not yet have a key:

Holothrix aphylla (Forssk.) Rchb.f. Nigeria to Yemen.
Holothrix arachnoidea (A.Rich.) Rchb.f. NE. Trop. Africa to Kenya, SW. Arabian Pen.
Holothrix elgonensis Summerh. Mt. Elgon of Uganda and Kenya.
Holothrix hydra P.J.Cribb Tanzania.
Holothrix klimkoana Szlach. & Marg. Angola.
Holothrix montigena Ridl. Ethiopia.
Holothrix nyasae Rolfe SW. Tanzania.
Holothrix pentadactyla (Summerh.) Summerh. Kenya.
Holothrix praecox Rchb.f. Zaïre, NW. Ethiopia.
Holothrix schimperi Rchb.f. Ethiopia to Kenya.
Holothrix socotrana Rolfe Socotra.
Holothrix squamata (Hochst. ex A.Rich.) Rchb.f. Ethiopia to Uganda.
Holothrix tridentata (Hook.f.) Rchb.f. Cameroon (Mt. Cameroon), Sudan to Ethiopia
Holothrix triloba (Rolfe) Kraenzl. SW. Tanzania.
Holothrix unifolia Rchb.f. Ethiopia (Gonder, Shewa)

World Checklist of Selected Plant Families. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the Internet; accessed 1/16/2010