Abstract:
The genus Tylosema belongs to the Caesalpiniaceae and includes four species of which only T. esculenturn and T. fassoglense occur in South Africa. The South African species are perennial creepers which produce tubers. The flowers which are distylous and zygomorphic, each contains two fertile stamens and eight staminodes. The flowers are borne in racemes on hapaxantic shoots. The morphology of the flowers, pollen and seed, the microsporogenesis, megasporogenesis, ultrastructure of the stigma and style, and the embryogenesis of the two species were investigated. The tetrasporangiate anthers give rise to tetrahedral microspore tetrads by simultaneous cytokinesis. The sporegenie caryokinesis occurs between 20h00 and 23h00. The monad, apolar and tricolporate pollen has a perforated tecturn and differs between T. esculentum and T. fassoglense with respect to the size and morphology of the grains. The stigma is of the wet type containing a secretion pro= duced by the unicellular stigmatic papillae lining the funnel-shaped stigma. A stylar canal occurs from the stig= ma to the ovary and is lined by two types of transmitting cells. The pollen tubes grow only alongside the parenchymatic transmitting cells which produce the stylar secre= tion. Each ovary has mostly two obcampylotropous ovules which are bitegmic and crassinucellate with a zig-zag micropylar canal. Of the linear tetrad only the chalazal megaspore develops into a Polygonum type of embryo sac. The ovular nucellus is relatively big with a conspicuous parietal tissue in the nucellar spout. The zygote develops into an embryo lacking a suspensor. The development of the embryo corresponds most closely with that of the Penaea variation of the Asterad type. The endosperm is nuclear, but is not completely absorbed by the developing embryo. The seeds are circular, symmetrical and anatropous with a crescent shaped hilum representing the scar where the funicle and its two aril lobes have separated from the seed. Sclerenchymatous palisade cells occur exotestally. The micropyle occurs alongside the lens where the palisade cells are the shortest. The pre- and post-chalazal vascular tissues, comprising three and two vascular bundles respectively, are equal in length.
