Disa virginalis (Diseae: Orchidoideae: Orchidaceae): A New Species from Southern Africa

Abstract

A new species of Disa, the largest genus of terrestrial orchids in southern Africa, is described from the Western Cape. Disa virginalis, sp. nov., was previously included in D. maculata, but is white rather than blue, with shorter and broader lateral sepals, and a less developed spur. In addition, the galea is narrowed in front. Similarities to D. schizodioides are also discussed; these indicate that the current sectional classification of subgenus Disa may not be correct. Disa P. J. Bergius, with ca. 130 species, is the largest genus in the subtribe Disinae. The three other genera in the subtribe, Monadenia Lindley, Herschelianthe Rauschert, and Schizodium Lindley, each has less than 20 species. Disa is widespread in the cooler parts of Africa. The majority of the species are found in the mountains and on the coastal flats of the southwestern tip of South Africa, and the genus is also common in the montane grasslands from the Drakensberg northward to Ethiopia and westward to Liberia. A single species is found in Yemen (Linder, 1983). The generic delimitation of the genus remains contentious, and it is possible that the satellite genera Herschelianthe and Monadenia should be included within Disa (Linder & Kurzweil, 1994). Although Linder (1981) published a detailed subgeneric classification for Disa, many of the sections and subgenera may not be monophyletic, and so need further evaluation (Linder, 1986; Linder & Kurzweil, 1990). With the increasing interest in the relationship between pollinators and floral morphology, much research has been done on the Disas (Johnson, 1994, 1995a, 1995b, 1995c; Johnson & Linder, 1995), and this interest has led to the discovery of several new species, one of which is described here. Disa virginalis H. P. Linder, sp. nov. TYPE: South Africa. Western Cape: Groot Winterhoek Forest Reserve, on dry rock ledges, Linder 6598 (holotype, BOL). Figure 1. A Disa maculata L.f. floribus parvis albis et petalis brevibus latis, a D. schizodioides Sonder lobis basalibus petalorum expansis et labiis aequantibus sepala recedit. Plants small, herbaceous, perennating by narrowly ovate testicular tuberoids to 1 mm long. Leaves dimorphic: basal leaves green, 3-6, linearoblanceolate, to 40 x 4 mm, acute to finely apiculate, the margins sometimes red, the upper subcauline with a purple-dotted sheath; cauline leaves reduced to membranous, brown-veined, to 15 mm long, acute sheaths, grading into the bract. Flower solitary, not resupinated, white except for vertical purple barring on the petal blades and a green galea sac, not scented. Ovary 10-20 long, exceeding the bract. Lateral sepals spreading, obovate, obtuse, obscurely apiculate, 10-17 x 8-15 mm. Dorsal sepal galeate, triangular in side view, laterally compressed, the apex attenuated, acute, somewhat reflexed, the back acute but without a developed spur, galea 10-15 mm tall and 4-6 mm deep, the entrance 3-5 mm wide. Petal limbs reflexed along the base of the galea, 4-6 x 1 mm; terminal blades obovate, ca. 5 x 3 mm, obtuse, upcurved geniculately behind the anther and twisted to face forward. Lip spreading, lorate to lorate-oblanceolate, acute, flat, 10-15 x 4-6 mm. Anther reflexed parallel to the petal limbs, 2.5 mm long, caudicles short and sharply upcurved. Rostellum equally three-lobed, 2 mm tall, robust, with the viscidia facing upward. Stigma small, horizontal, tripulvi-