Abstract
The seed morphology of 151 species of Southern AfricanOrchidoideae (Orchideae andDiseae; sensuDressler 1981) was studied by means of scanning electron microscopy. Two different seed types were found. (1) In the majority of species the seeds are minute and fusiform. The seed coat is made up of comparatively few concave and elongate testa cells with straight or slightly undulate and generally unthickened anticlinal cell walls. The seed type was here termed “Satyrium-type”. While most species are very similar in the ornamentation of the periclinal walls of their seed coat, considerable variation was found inHolothrix where two distinct groups can be recognized in this respect. (2) A remarkably different seed type was observed inDisa uniflora and three apparently closely related species (“Disa uniflora-type”), where large balloon-like seeds occur. Their seed coat consists of convex cells with undulate anticlinal walls. It is suggested that this seed type is a derived condition and has evolved in adaptation to the specialized habitat alongside streams. The possibility of hydrochory in these four species is briefly discussed.
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