A synopsis of the southern African members of the genera Dicoma Cass. and Macledium Cass. (family Asteraceae, subfamily Cichorioidiae, tribe Mutiseae, subtribe Gochnatiinae) is presented. The most recent monograph of Dicoma was done by Wilson (1923). It included 34 species, of which 17 are southern African, The southern African species were last treated by Harvey (1865). Traditionally Dicoma included 50 to 65 species, of which 23 occur in southern Africa. Ortiz (2001) reinstated the genus Macledium Cass., which was first described by Cassini (1825), following a phylogenetic study of Dicoma and related genera (Ortiz, 2000). The species previously belonging to sections Macledium and Pterocoma of the genus Dicoma have been transferred to the genus Macledium by Ortiz (2001). In this study, characters relating to morphology of the involucral bracts, disc floret cuticle ornamentation, type of pappus and the type of achenes are used to distinguish the two genera. Differences were found between the grassland species and Cape species of Macledium. Type of florets in the capitulum and pappus morphology are used to distinguish sections within Dicoma sensu stricto. Characters such as habit, leaf morphology, shape and size of the capitulum, involucral bracts vestiture and details of the pappus could be reliably used to distinguish species. The genus Dicoma now consists of about 35 species, of which16 species and two subspecies occur in southern Africa. Four informal groups of D. anomala subsp. anomala, two of D. anomala subsp. gerrardii as well as two of D. montana are recognized to accommodate infraspecific variation. Macledium comprises about 20 species, of which seven species, three subspecies and three varieties occurr in this region. M. spinosum is divided into two informal forms and a new combination, Macledium zeyheri subsp. zeyheri var. thyrsiflorum, is made. In view of the above, a comprehensive taxonomic revision of all the southern African taxa was done. Morphological and anatomical data were used to investigate relationships among the species of Dicoma sensu stricto, using the genus Macledium as the sister group. A phylogenetic analysis of Macledium was also done to investigate relationships between the grassland species and the Cape species. The taxonomic treatment includes the nomenclature, synonymy, diagnostic characters, uses, common names (where possible) and geographical distribution for all southern African taxa belonging to the two genera. Keys to the genera, sections, species and subspecies are provided and the diagnostic characters of the two genera are illustrated. / Prof. B.E. van Wyk
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:8311 |
| Date | 21 April 2008 |
| Creators | Netnou, Noluthando C. |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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