The systematics of the genus Garuleum cass. (Asteraceae)

[摘要] English: The aim of this study is to provide a taxonomic revision and molecular phylogenetic analysis of the eight Garuleum Cass. (Asteraceae) species of southern Africa. The taxonomic revision resulted in the construction of an identification key to the species, a revision of all type literature and nomenclature, clarification and designation of type specimens, compilation of morphological and micromorphological descriptions, distribution maps and ecological data for all Garuleum species. The molecular phylogenetic investigation resulted in the first complete phylogeny for the genus Garuleum, based on the nuclear gene region ITS and the chloroplast intergenic spacers trnT–trnF and psbA–trnH. All available type specimens related to Garuleum in southern Africa were studied. Where holotype specimens could not be located; lectotypes were designated from available isotypes or syntypes. In cases where only syntypes had been given by authors of species names, lectotypes were designated. Additional herbarium specimens on loan from several South African and European herbaria were investigated and additional material was collected in the field. These specimens were used to compile morphological descriptions and distribution maps. Micromorphological investigation of leaf surfaces, fruit, flowers and pollen was also completed. Garuleum species are aromatic, herbaceous shrubs with the inflorescence arranged in a capitulum composed of white or mauve coloured ray florets and yellow disc florets. The abaxial and adaxial leaf surfaces, leaf structure and involucral bract sizes are important for species identification. Garuleum is widely distributed over southern Africa, with the majority of the species found in the Eastern Cape. Some species, such as G. album, have restricted distribution ranges while others, such as G. bipinnatum, are very common and widely distributed. The annual precipitation of a specific region, in addition to altitude are possibly important factors influencing the biogeography and evolution of the eight species. Heterocarpy has evolved in G. bipinnatum, providing this species with an ability to survive in frequently disturbed areas and to distribute widely. Garuleum schinzii also has a wide distribution and may have the ability to reproduce through heterocarpy. The rest of the Garuleum species have more restricted distribution ranges and only reproduce through homocarpy. The micromorphological characters of the leaves of Garuleum are not taxonomically informative, due to their intraspecific variability. Micromorphological analysis of the flowers of the different species indicated that trichome complement on ray- and disc floret corollas may be taxonomically important. The micromorphology of the epidermal surfaces of achenes from different species is informative for species identification. The micromorphology of the pollen is not sufficiently variable for species level identification, but does support the monophyly of the genus. The phylogeny obtained from the combined nuclear and chloroplast regions revealed that G. latifolium may belong to the earliest diverging lineage within the genus. The rest of the species are divided into two sister clades. Clade A consists of G. album, G. sonchifolium, G. schinzii and G. woodii. Clade B consists of G. bipinnatum, G. pinnatifidum and G. tanacetifolium. The position of G. schinzii in clade A is poorly supported, while the morphology and geographic proximity of this species to the species in clade B, suggests that G. schinzii belongs in clade B. This phylogeny, in combination with geographical, micromorphological and morphological data provided insight into a possible point of origin for the genus in Kwazulu-Natal or the northern parts of the Eastern Cape. The topography of the Drakensberg may have influenced the distribution routes of the different species, forcing distribution either along the coast or into the interior of Southern Africa by acting as a barrier.

[发布机构] University of the Free State