Systematics/Phytogeography / Taxonomie/ Section
Nickrent, Daniel , García, Miguel , Mucina, Ladislav .
A phylogeny of Thesium (Santalaceae) using nuclear ribosomal ITS sequences.
With over 300 species, Thesium is the largest genus in Santalales. Worldwide in distribution, its highest diversity is in South Africa. Regional taxonomic works exist yet no modern comprehensive phylogenetic study is available. Thesium samples throughout its distribution were obtained and nuclear ribosomal ITS sequenced. Of the 294 sequences, 282 were from Thesium representing 165 names. Heuristic searches using MP did not finish, however, the strict consensus tree yielded a number of meaningful clades. With Buckleya as outgroup, Osyridocarpos and Thesium lineatum were sister to the remaining taxa, thus indicating that this Thesium should be recognized as a separate genus. These taxa formed two clades: A (Thesidium, Kunkeliella and Eurasian Thesium species) and B (mainly South and tropical Africa). Thesium mauritanicum of North Africa was sister to all other clade A taxa, but within this clade little of the phylogenetic structure proposed by Hendrych was seen. Chrysothesium was not basalmost in Thesium nor monophyletic but related to Asian species in Section Macranthia. Thesium spinosum and T. spinulosum were sister to the other clade B species. Plants with dichasial inflorescences occur in the next two clades (Section Imberbia Subsection Subglabra). The next clade is composed entirely of South African taxa, yet contains species assigned to both Sections Barbata and Annulata. The central portion of clade B contains mostly tropical African taxa, some of which form a clade approximately corresponding to Section Imberbia. Two of the three South American species (Section Psilothesium) are nested within the tropical African clade, thus their recognition as genus Austroamericium is not supported. Three Malagasy species also occur in this tropical African clade but are distantly related. The remainder of clade B is composed of ca. 30 taxa, all from Section Barbata. ITS sequences will continue to provide important data needed for a future revision of Thesium.
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1 - Southern Illinois University, Department of Plant Biology, 1125 Lincoln Drive, Carbondale, Illinois, 62901-6509, USA
2 - Real Jardín Botánico, CSIC, Plaza de Murillo 2, 28014 Madrid, Spain
3 - University of Stellenbosch, Department of Botany & Zoology, Private Bag X1, 7602 Matieland, Stellenbosch, South Africa
Presentation Type: Oral Paper:Papers for Sections
Location: Room 6/Woodward
Date: Tuesday, July 29th, 2008
Time: 11:30 AM