A search for taxonomically informative characters in the large genus Heliophila L. (Brassicaceae/Cruciferae)

Thesis (MSc)--Stellenbosch University, 2002.

ENGLISH ABSTRACT:Several authors regard the subdivision of the large genus Heliophila as unsatisfactory and in need of a detailed taxonomic study. Previous studies on this genus were based exclusively on gross external morphological characters. The present study investigates patterns of variation in Heliophila in order to identify taxonomically informative characters that could be used in the subdivision of this large genus. The study differs from previous studies in Heliophila because, in addition to macro-morphology, it employs micro- morphological (SEM) and palynological evidence to elucidate the subdivisio.n of Heliophila. The study emanates from a taxonomic revision of Heliophila proposed by Sander (1860), in which he subdivided the genus into six sections, based on the variation in fruit characters. Subsequent authors ignored the sections, regarding the generic subdivision as insufficiently supported, hence unsatisfactory . The results of cluster analysis, which are based on all the characters examined in the study (overall variation), propose the subdivision of Heliophila into three main clades: Micromorphological characters of fruits, seeds, and leaves are consistently found to be more congruent with the phenogram than macro-morphological characters of the same organs. This suggests that micro-morphological characters are taxonomically informative in Heliophila and should prove very important in a future phylogenetic classification of the genus. Palynological characters were found to be of limited taxonomic importance in the subdivision of the genus.

AFRIKAANSE OPSOMMING: Verskeie outeurs beskou die onderverdeling van die groot genus Heliophila as onbevredigend, en meen dat dit 'n gedetaileerde taksonomies studie benodig. Vorige studies op hierdie genus het slegs op ekstern morfologiese kenmerke gekonsentreer. In die huidige studie word patrone van variasie in Heliophila ondersoek met die oog op 'n moontlike onderverdeling van die genus, en taksonomies betek~nisvolle kenmerke wat in hierdie verband gebruik kan word, word geidentifiseer. Die huidige stud'e verskil van vorige studies daarin dat, benewens makro-morfologiese kenmerke, dit ook mikro-~rfologiese tegnieke (SEM) en palinologiese kenmerke gebruik om 'n sinvolle subverdeling van Heliophila te probeer vind. Die huidige studie spruit uit 'n taksonomiese hersiening van Heliophila deur Sonder (1860), waarin hy voorstel dat die genus in ses seksies verdeel word op grond van variasie in vrug kenmerke. Hierdie generiese onderverdeling en die voorgestelde seksies is deur latere outeurs as onbevredigend beskou, en is meestal in die literatuur geignoreer. Die resultate van fenetiese analise, wat op alle ingeslote kenmerke gebaseer is (algehele variasie), stel voor dat Heliophila in drie hoof groepe verdeel moet word. Taksonomies belangrike kenmerke wat hierdie onderverdeling ondersteun sluit in blaartipe, variasie in blaar-oppervlakke (SEM), variasie in die aard van die saadhuid (SEM) en variasie in vrugoppervlakke (SEM). Palinologiese en makro-morfologiese kenmerke was van geringe waarde in die onderverdeling van die genus.