A taxonomic study of Cryptolepis (Apocynaceae) in southern Africa
A taxonomic revision of Cryptolepis R.Br. (Apocynaceae, Periplocoideae) in southern Africa is presented. This revision comprises investigations into the micromorphology of pollen, translators, leaf anatomy, leaf epidermal surfaces and seed coat surfaces; macro-morphology of the plant parts; nomenclature, geographical distribution and ecological characteristics of the six species indigenous to southern Africa. The investigations resulted in descriptions with appropriate nomenclature and the compilation of an identification key for the six species. All available type specimens related to Cryptolepis in southern Africa were studied. Where holotype specimens could not be located lectotypes were designated from available isotypes or syntypes. Where no isotypes or syntypes could be located, neotypes were declared. In cases where only syntypes had been given by authors of species names, lectotypes were declared. Cryptolepis is widely distributed throughout the northern parts of southern Africa, with the largest concentration of species in the north-east of the region. Some species, such as C. oblongifolia, are common, while others have very restricted distribution ranges. C. delagoensis, for instance, is known from only six localities in southern Africa. Only C. decidua occurs in the desert and semi-desert habitats in the north-west of southern Africa, while the other five species inhabit savannah, sand forest, riverine -, afromontane - and coastal vegetation in the eastern parts of the region. In southern Africa Cryptolepis consists of slender climbers, occasionally small suffrutices or branching shrubs with white latex and interpetiolar ridges with dentate colleters. Leaves are opposite, decussate or rarely fascicled. A combination of leaf anatomy and leaf surface characteristics proved to be taxonomically useful for distinguishing the southern African species. The fruit consists of paired follicles. Seeds of Cryptolepis are adapted to anemochoric dispersal through a coma of hair at the micropylar end. All southern African species can be differentiated from each other using cellular arrangement and primary and secondary sculpture of their seed coat surfaces. Floral characteristics are taxonomically useful for distinguishing Cryptolepis from related genera. Cryptolepis is characterized by a distinct corolla tube, with corolla lobes always longer than the corolla tube, corona lobes arising just above the middle of the corolla tube, and usually included in the corolla tube, and stamens arising at the lower third of the corolla tube, with interstaminal discs always present. Two, semi-inferior, apocarpous ovaries are present. The styles unite to form a compound style and pentagonal style-head, on which five translators are formed by epithelial cells in grooves alternating with the stamens. The anthers are fused to the style head, forming a gynostegium. In the five species that occur in the eastern parts of the region flowers are arranged in cymes. Prominent, paired colleters are found at the inner bases of the sepals. The corona lobes may be oblong, clavate, deltoid or awl-shaped. The corona lobes are always included in the corolla tube, where they touch or fit tightly, forming a dome which closes off the lower corolla tube. Pollen characteristics and translator shape are similar for all five species and have little taxonomic value. C. decidua differs from the eastern species in that its flowers are solitary. The colleters at the inner sepal bases are replaced by trichomes. The corona lobes are filiform, do not form a dome over the lower corolla tube and may be exserted from the corolla tube mouth. Pollen tetrad shape and translator shape and size differ markedly from those of the other species. All these unique characteristics in C. decidua suggest that this species may not belong in Cryptolepis.