AFRICAN

ORCHIDS

Disa P.J.Bergius, Descr. Pl. Cap.: 348 (1767).
Synonyms:
Repandra Lindl., Orchid. Scelet.: 12 (1826).
Penthea Lindl., Intr. Nat. Syst. Bot., ed. 2: 446 (1836).
Forficaria Lindl., Gen. Sp. Orchid. Pl.: 362 (1838).
Gamaria Raf., Fl. Tellur. 4: 49 (1838).
Herschelia Lindl., Gen. Sp. Orchid. Pl.: 362 (1838), nom. illeg.
Monadenia Lindl., Gen. Sp. Orchid. Pl.: 356 (1838).
Orthopenthea Rolfe in W.H.Harvey & auct. suc. (eds.), Fl. Cap. 5(3): 179 (1912).
Amphigena Rolfe in W.H.Harvey & auct. suc. (eds.), Fl. Cap. 5(2): 197 (1913).
Herschelianthe Rauschert, Feddes Repert. 94: 434 (1983).
× Herscheliodisa H.P.Linder, S. African Orchid J. 16: 102 (1985).


The genus Disa was established in 1767 by the Swedish botanist and physician Peter Jonas Bergius. There have been many suggestions as to the origin of the name. Börge Pettersson (1985) concluded that the genus was named for Queen Disa, a figure in Swedish mythology or legend, who was ordered to appear before the king neither clothed nor naked. She solved this problem by wearing a fishing net, and Pettersson believes that the net veining on the sepals of Disa unifiora (the type species of the genus) made Bergius think of the tale.
Description:
A large genus centred in South Africa, with 179 species currently recognized. All are terrestrial, or occasionally lithophytic, plants with round or cylindrical tubers, one dying back each year and a new one being formed for the following season's growth. Some species have foliage leaves borne on the flowering stem while others have sheathing leaves on the scape and foliage leaves on a separate sterile shoot. Almost all species have red or purple blotches at the base of either type of shoot.


Terrestrial (rarely lithophytic), growing from an underground tuber that is renewed each year; in a few species, stolons are produced that develop tubers at the ends so that the plants increase vegetatively. Stems usually leafy; separate sterile shoots with foliage leaves are produced in two sections and occasionally in a third. Inflorescence terminal, one- to many-flowered. Flowers often very showy—white, yellow, orange, pink, red, or purple, sometimes spotted—and usually resupinate. Dorsal sepal spurred, forming a deep or a shallow hood; lateral sepals usually spreading; petals small, often inside the hood. Lip small, narrow. Column short; anther erect, horizontal, or reflexed. Rostellum small, trilobed, lying between the anther and the cushion like stigma. Pollinia two, caudicles two, viscidia two.


The most distinctive feature of the genus is that the spur is formed from the dorsal sepal, rather than the lip. This is also the case in the related genera Brownleea and Herschelianthe, but the former can be distinguished by the minute lip which clasps the column and the latter by the grass-like leaves in a basal tuft, blue flowers and large, usually fimbriata lip.
Distribution:
The genus, is widespread in tropical and South Africa, with a few species occurring in Madagascar and Réunion, and one extending into Arabia.
Notes:
In H.P. Linder (1981)´s revision of Disa Berg. excluding sect. micranthae Lindl. The morphological variation in the genus allows the recognition of 15 sections, grouped into five subgenera. As these taxa are natural, it is difficult to isolate any characters that will rigorously distinguish any one taxon from all the others. The subgenera are based largely on gynostemium and petal characters, not for any theoretical reason but mainly because these two structures are mostly correlated. Phytogeographically and ecologically the subgenera also seem to form fairly homogeneous entities. The subgenera may be distinguished as follows:
A key to the subgenera can be seen here. And a key to the section here where you also can find all the species of Disa.

Which I have chosen to follow on this page, but see below the section news.

Species without a key

Disa alinae Szlach., Zaïre
Disa danielae Geerinck, S. Zaïre
Disa facula P.J.Cribb, C.Herrm. & Sebsebe, Ethiopia
Disa lisowskii Szlach., Zaïre
Disa renziana Szlach., Zaïre

Species without a key in the section Schizodium

Disa bifida (Thunb.) Sw., SW. & S. Cape Prov.
Disa biflora (L.) Druce, SW. Cape Prov.
Disa flexuosa (L.) Sw., WSW. & SW. Cape Prov.
Disa inflexa (Lindl.) Mundt ex Bolus, SW. & S. Cape Prov.
Disa longipetala (Lindl.) Bolus, SW. Cape Prov.
Disa obliqua (Lindl.) Bolus, SW. Cape Prov.

News:
The genus Disa is currently divided into five subgenera: Micranthae, Falcipetalum, Hircicornes, Stenocarpa and Disa (Linder, 1981c, 1986; Linder & Kurzweil, 1999; Kurzweil & Linder, 2001). These subgenera do not reflect phylogenetic relationships and we ((Benny Bytebier*, Dirk U. Bellstedt & H. Peter Linder))therefore propose not to recognise them any longer. At this level in the phylogeny the relationships are very complex, and no obvious taxa can be readily established that would group the sections, such that they are morphologically defined and not excessive in number.
We (Benny Bytebier, Dirk U. Bellstedt & H. Peter Linder 2008) propose several changes at sectional level, which include recognizing Schizodium as a section of Disa rather than as a separate genus. We have tried to minimize the number of changes, but believe it is important to have an evolutionary-based taxonomy as it will help ongoing research on mimicry and pollination (e.g., Johnson & al., 1998). Furthermore, the horticultural industry, which is largely based on hybridisation, will benefit from a classification that better reflects evolutionary relationships.


Cultivation:
Disa includes some of the most beautiful of African orchids-indeed of all orchids-but relatively few are in cultivation; this is probably due to a mixture of being difficult to obtain, and difficult to grow.


The species of disa commonly in cultivation and their hybrids are evergreen and restricted in the wild to the southern tip of South Africa, the Cape area. Usually referred to as the Disa uniflora group, it contains D. aurata, D. caulescens, D. cardinalis and D. tripetaloides. All are usually found in permanently moist or downright boggy conditions such as streamsides, growing either in free-draining sand or open organic litter with excellent drainage and a low (acidic) pH. The three crucial factors for successful disa cultivation are temperature, water quality and ventilation to mimic these growing conditions.
Water is critical, as disas abhor calcium, and soon signal their dislike for it in yellowing foliage and poor growth. In hard water areas, soft rainwater or de-ionised water is a must. You can kill disas in a week with the wrong kind of water, agrees Dave.
The uniflora group is among the hardiest of the genus; D. uniflora is found up to 1,200m (4,000ft) and survives a few degrees of frost. Dave is trialling some plants outdoors over winter, but keeps the polytunnel housing the bulk of his collection at a minimum 10°C (50°F). The tunnel is well-vented, especially in summer. Electric fans keep the air moving, cooling the inside and discouraging fungal infections. He keeps his plants mostly in square plastic pots sitting in trays of soft water, which is topped up as necessary.


There are almost as many compost recipes as disa growers, but the prime consideration is that it must be free-draining to allow air into the constantly damp mixture. Dave's 50:50 mix of perlite and peat seems to suit all his plants, whatever size, while expanded clay (Seramis), live sphagnum moss and even sharp sand are popular with other growers. The rule with feeding is little and often with a balanced formula when in active growth, but given their sensitivity to dissolved salts, err on the side of dilution.


Disas grow from underground tubers or stolons (stems adapted for storage) and bloom in summer. After flowering, a rosette often browns and dies back, but this is the normal growth pattern. New shoots should quickly begin to emerge, and the best time to repot is as these appear. Wash away the old compost carefully from the delicate roots, dividing up crowded tubers, and repot into fresh growing medium. If peat-based formulas are used, an annual repotting is advisable because the compost spends much of its time wet.


Give disas a cool, protected environment and soft water and they are no more difficult to grow than many carnivorous plant species. These two groups are grown in similar conditions and inspire the same fascination for their devotees. Insect-eating species may be intriguing, but in the flowering stakes, the exceptionally beautiful and richly coloured blooms of disas win hands down.
Bibliography and References:
Backhouse G. 2000 The occurrence of the South African orchid Disa bracteata Sw in Victoria. Austral. Orchid Rev. 65. (5): 22 (2000)
Cribb PJ, Herrmann C, Demissew Sebsebe. 2002 New records of orchids from Ethiopia. Lindleyana 17. (1): 178-188 (2002)
Geerinck, D. (1974) Notes taxonomiques sur des Orchidacées d'Afrique centrale, II: Disa Berg. Bulletin de la Societe Royale de Botanique de Belgique, 107(1), 61-67.
Kurzweil H, Liltved WR, Linder HP. 1997 Disa introrsa sp. nov. (Orchidaceae) from the western Cape of South Africa, with notes on the phylogeny of Disa sect. Disella. Nordic J. Bot. 17. (4): 353-360 (1997)
La Croix I. 1997 African terrestrial orchids: the other Disas. Orchid Rev. 105. (1218): 360-366).
Linder H.P. 1981d. — Taxonomic studies in the Disinae (Orchidaceae). IV. A revision of Disa Berg.
Linder HP, Johnson SD, Liltved WR. 1998 Disa virginalis (Diseae: Orchidoideae: Orchidaceae): a new species from Southern Africa. Novon 8. (4): 405-407 (1998)
Linder, H. P. (1981a) Taxonomic studies on the Disinae. I. A revision of the genus Brownleea Lindl. Journ. S. Afr. Bot. 47: 13-48.
Linder, H. P. (1981b) Taxonomic studies on the Disinae. II. A revision of the genus Schizodium Lindl. Journ. S. Afr. Bot. 47: 339-371.
Linder, H. P. (1981c) Taxonomic studies on the Disinae. III. A revision of the genus Disa Berg., excluding sect. Micranthae Lindl. Contrib. Bol. Herb. (in print).
Pridgeon AM. 1999 Anatomy. In: Pridgeon, A, M, , Cribb, P, J, , Chase, M, W, , Rasmussen, F, N ed(s). Genera Orchidacearum. Volume 1.
Schlechter, R. (1901) Monographie der Diseae. Bot. Jahrb. 31: 134-313.
Stewart, J. (1973) Disa woodii. S. A/r. Orch. Journ. 3: 7-8.
Stoutamire W. 1990 Disas in South Africa. Amer. Orchid Soc. Bull. 59. (8): 782-785 (1990)
Szlachetko DL. 1994 Orchidaceae Lisowskianae: 3. Disa and Tridactyle. Fragm. Flor. Geobot. 39. (2): 543-548 (1994)
Vogelpoel L, Van der Merwe DW, Anderson BD. 1985 A white form of Disa racemosa: a rare mutant with a great future. Amer. Orchid Soc. Bull., 54. (1): 47-51 (1985)
Vogelpoel L. 1980 Disa uniflora - its propagation and cultivation. Amer. Orchid Soc. Bull. 49. (9): 961 - 972 (1980)
Vogelpoel L. 1980 Orchids of Africa: Disa species and their hybrids. Amer. Orchid Soc. Bull. 49. (10): 1084 - 1092 (1980)
Vogelpoel L. 1991 Disa hybridisation in the western Cape, current status and future prospects: part 1. General perspective. S. Afr. Orchid J. 22. (4): 74-81 (1991
Vogelpoel L. 1993 The blue Disas: part 1. Blue Disa species. S. Afr. Orchid J. 24. (3): 66-72 (1993)
Vogelpoel L. 1993 The blue Disas: part 2. The blue Herschelianthes. S. Afr. Orchid J. 24.