Holothrix Lindl. , Gen. Sp. Orchid. Pl.: 257, 283 (1835), nom. conserv.
Monotris Lindl., Edwards's Bot. Reg. 20: t. 1701 (1834).
Scopularia Lindl., Edwards's Bot. Reg. 20: t. 1701 (1834).
Saccidium Lindl., Gen. Sp. Orchid. Pl.: 301 (1835).
Tryphia Lindl., Edwards's Bot. Reg. 20: t. 1701 (1835).
Bucculina Lindl., Companion Bot. Mag. 2: 209 (1837).
Deroemera Rchb.f., De Pollin. Orchid.: 29 (1852).
Plants terrestrial or lithophytic, tuberous; leaves l .I or 2, ovate or orbicular, flat on the ground, some-times withering before anthesis; scape erect, un-branched, usually pubescent, with or without bracts. Inflorescences spikes, usually second or sub second. Flowers: Sepals subequal, sometimes I connate, smaller than the petals. Petals entire or fimbriate. Lip fleshy or membranous, usually divided into 3 to many lobes, rarely entire, produced into a spur. Gynostemium small, erect; pollinia 2, sectile, each with a short caudicle and separate viscidium.
Type species: Holothrix brevipetala Immelman & Schelpe & Schelpe.
Trop. & S. Africa, SW. Arabian Pen.
Not in cultivation.
The plants of this genus are very characteristic, with often hairy, heart-shaped leaves flat on the ground, and with minute flowers. Several species are very drought resistant, and in many semi-arid areas are the only orchids found. Even in more mesic areas Holothrix is often found in locally dry habitats such as on rock faces. Biologically this genus is fascinating, with its adaptations to survive drought and its minute flowers, but it has scarcely been studied, and nothing is known about its pollination and reproductive biology, nor of its drought-surviving mechanisms.
Hairy stems and flat, hairy leaves of most species, frequently divided lips and petals, an almost identical gynostemium structure, and a similar distribution are shared with Bartholina and suggest a very close relationship between the two genera. Bartholina and Holothrix together are the most distinctive group in the whole subtribe Orchidinae.
The water-storing upper leaf epidermis is an interesting feature of Holothrix, and is probably derived. The feature has also, probably independently, evolved in the genus Satyrium. Whatever the phylogenetic significance of the water-storing leaf tissue is, it is certainly what enabled the genus to colonize the dry parts of southern Africa.
Key to the area around Malawi, Mozambique, Zambia, Zimbabwe and Botswana,and Key to the area around Southern Africa and Holothrix species some not yet have a key:
Bibliography and References:
Archer C, Archer A new species of Holothrix Lindl. from northern KwaZulu-Natal. S. Afr. J. Bot. 62. (4): 209-211 (1996)
Cribb PJ. New or little known orchids from East Africa. Kew Bull. 34. (2): 321 - 340 (1979)
Cribb PJ. New records of Orchidaceae for Arabia. Kew Bull. 42. (2): 461-463 (1987)
Cribb PJ. The orchids of Arabia. Kew Bull. 33. (4): 651 - 678 (1979)
Kurzweil H, Weber A. Floral morphology of southern African Orchideae. I. Orchidinae. Nordic J. Bot. 11. 155-78.(1991)
Linder HP, Kurzweil H. The phylogeny and classification of the diseae .Ann. missouri Bot. Gard. 81. 687-713.(1994)
Linder, H.P. & Kurzweil, H. 1999. Orchids of southern Africa. Rotterdam: A.A. Balkema.
Schelpe EA. A review of the summer rainfall area species of Holothrix in South Africa. S. Afr. Orchid J. 8. (1): 5 - 6 (1977)
Szlachetko DL, Margonska HB. Holothrix klimkoana Szlach. & Marg. a new species from Angola. Candollea 61. (2): 467-470.(2006)
Van der Walt H, Van der Walt M. Holothrix: a new species. S. Afr. Orchid J. 26. (1): 16-17 (1995)
Williamson G. A desert orchid. Orchid Rev. 89. (1050): 106 - 107 (1981)
Wodrich, K. 1997. Growing South African indigenous orchids. Rotterdam: A.A. Balkema.