Abstract
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