Taxonomy of the genera baseonema, batesanthus, mangenotia, mondia, sacleuxia, sarcorrhiza and zacateza (Periplocoideae, apocynaceae)

Abstract

English: Seven genera of the African Periplocoideae namely: Baseonema Schltr. & Rendie, Batesanthus N.E. Br., Mangenotia Pichon, Mondia Skeels, Sacleuxia Baill., Sarcorrhiza Bullock and Zacateza Bullock are presented in this study, with special reference to taxonomy. A complete account of taxonomic literature, keys as well as known geographical distribution of the seven genera is given. The type specimens (in red) and all other specimens studied are presented in Appendix B. The character states and/or features used to delimit genera are circumscribed. Floral and vegetative morphology have been extensively studied with the aid of a stereo-microscope and represented in the form of diagrammatic sketches or photographic figures. Floral (i.e. corolla, corona, androecium and gynoecium) features are important to delimit between species. For instance, Sacleuxia tuberosa is characterised by having a hairy ovary and the anthers in Mangenotia are hairy. Mondia whitei has an obcordate corona lobe with two dorsal processes. Most of the genera co-exist as shrubs and very rarely lianas, but Sarcorrhiza is outstanding as an epiphyte. To complement "traditional taxonomy", pollen and translator morphology, leaf and seed morphology have been studied, with the aid of LM, SEM and TEM. The pollen is uniform in morphology, with all the genera having pollen in tetrads and little variation between the species. However, pollen grain size can be used to a certain extent so as to distinguish between species, for example, the largest tetrads are found in species of Baseonema gregorii & Mondia whitei (Figure 4). One other important feature is the number of pores per grain. Most of the Periplocoids are characterised by having 4-6 pores per grain. This, however, does not apply to multi-parate Baseonema having 8-10 pores per grain, a character so far only known in species of Raphionacme and Schlechterella. Individual grains of a tetrad are held together by wall bridges. The exine is smooth and consists of an outer homogenous stratum (tectum) subtended by a granular stratum. The intine is well developed. The layers turn out to be of little taxonomic value. Translators are similar in structure, with three parts distinguished, the spoon, the stalk and an adhesive disc (viscidium). The whole translator varies in size (although marginal difference is small) within the species (Table 4.2). The character state of taxonomic value in the leaf surface is the presence of papillae in Mangenotia eburnea. The cuticle on the leaf is variously striated or smooth. The paracytic stomata and smooth or warty, unicellular trichomes have been found to be of little taxonomic value especially at generic level. However, at species level, the amphistomatous condition of Sacleuxia tuberosa might be of taxonomic value. Trichomes are present on the leaf surface of all taxa except for Batesanthus parviflorus and Batesanthus purpureus with glabrous leaf surface. Seeds are characterised by having a coma of hairs. The exception is Batesanthus intrusus with a fringe of hairs around the entire margin.

Afrikaans: Sewe genera van die Periplocoideae uit Afrika, naamlik Baseonema Schltr. & Rendie, Batesanthus N.E. Br., Mangenotia Pichon, Mondia Skeels, Sac/euxia Baill., Sarcorrhiza Bullock and Zacateza Bullock is taksonomies ondersoek. 'n Volledige uiteensetting van die taksonomiese literatuur, sleutels sowel as die geografiese verspreiding van die sewe genera word gegee. Die tipeeksemplare (in rooi) en al die bestudeerde eksemplare is in Aanhangsel B gelys. Die kenmerke en/of strukture wat gebruik is om die genera te omgrens, is beskryf. Blommorfologie en vegetatiewe kenmerke is intensief met 'n stereomikroskoop bestudeer en die resultate is in die vorm van sketse en foto's aangebied. Blomkenmerke (bv. kroon, bykroon, androesium en ginoesium) is belangrik vir die onderskeiding van spesies. Sac/euxia tuberosa word deur 'n harige vrugbeginsel terwyl Mangenotia deur harige helmknoppe gekenmerk. Die meeste genera kom as struike voor en selde as liane. Sarrcorhiza kom egter as 'n epifiet voor. Om die morfologiese ondersoek uit te brei, is stuifmeel, stuifmeeldraers, blaaroppervlak en sade ook met die LM, SEM en TEM (stuifmeel) bestudeer. Die tipiese Periplocoideae tetrades kom in al sewe genera voor met relatief min variasie tussen die spesies. Die meeste Periplocoideae word gekenmerk deur 4-6 porieë per stuifmeelkorrel. In Baseonema kom 8-10 porieë per stuifmeelkorrel voor, 'n kenmerk wat tot dusver net bekend was in spesies van Raphionacme en Sch/echterella. Individuele stuifmeelkorrels van 'n tetrade word by mekaar gehou deur wandbrue. Die eksien is glad en bestaan uit 'n homogene stratum (tektum) wat begrens word deur 'n granulêre stratum. Die intien is goed ontwikkel. Die wandlae van die stuifmeelkorrel is nie van taksonomiese waarde nie. Blaaroppervlakkenmerke wat van taksonomiese waarde is, is: die teenwoordigheid van papille in Mangenotia eburnea. Die kutikula op die blare is gestrieerd of glad. Die parasitiese stomata en gladde of vratagtige, eensellige trigome is van min taksonomiese waarde, veralop genusvlak. Op spesievlak kan die amfistomatiese blare van Sacleuxia tuberosa taksonomiese waarde besit. Trigome kom op die blaaroppervlak van al die taksa voor met die uittsondering van Batesanthus parviflorus en Batesanthus purpureus waar geen trigome voorkom nie. Sade word gekenmerk deur 'n koma van hare. By Batesanthus intrusus kom die trigome egter op die rand van die saad voor.