The systematic revision of Chaetanthera Ruiz & Pav., and the reinstatement of the genus Oriastrum Poepp. & Endl. (Asteraceae; Mutisieae)

Chaetanthera Ruiz & Pav. (30 species, 1 variety, 2 hybrid
forms) and Oriastrum Poepp. & Endl. (18 species, 1 variety) are
among the most species-rich Astereaceae genera of the Chilean
Flora. Formerly combined under one name, the two genera have been
extensively revised. Chaetanthera is found mainly in Chile, with
one Peruvian species and several scattered populations of other
species in Andean Argentina. Oriastrum inhabits the higher
elevations of the Andes, spread over Chile, Argentina, Bolivia and
Peru. Systematic studies focussing on morphological and anatomical
variation of characters taken from habit, involucral bracts, and
achenes, combined with palynological and genetic (nr DNA)
information are used to circumscribe Chaetanthera with two
subgenera – Chaetanthera subgenus Chaetanthera and Chaetanthera
subgenus Tylloma (D.Don) Less., and reinstate Oriastrum with two
subgenera – Oriastrum subgenus Oriastrum and Oriastrum subgenus
Egania (J.Rémy) A.M.R. Davies. Character variation is discussed in
the context of form, function and habitat, with emphasis on the
evolutionary adaptiveness of character traits seen in the two
allied genera. Chaetanthera appears to show primary adaptation to
cold and several secondary adaptations to arid conditions, typical
of modern Chilean landscapes. Oriastrum taxa appear well-adapted to
the cold, high elevations of the Andes, and show secondary
developments trending towards an insular syndrome. The collated
bio-geographical information of the taxa is considered in terms of
endemism, hotspots and species radiations. Chaetanthera taxa have 2
loci of diversity hotspots in Chile – in Coquimbo and in Santiago.
Trichome diversity and capitula morphology trends are used as
evidence of species radiations in Chaetanthera. Oriastrum taxa are
notable for parallel radiations of morphologically similar species
within particular Andean zones: i.e., Altoandino or Altiplano. Case
studies concerning three groups of Chaetanthera taxa are presented.
The first case highlights the effect of the El Niño on the
polymorphic C. glabrata along the Chilean Pacific coast. The second
case deals with current active hybridisation between C. linearis
and C. albiflora in the semi-arid Andean foothills. In the last
example, incipient speciation and polymorphism between C. chilensis
and C. elegans in southern Central Chile is discussed. Various
statistical techniques for the analysis of hybridisation events are
applied. All taxa are keyed out and described. Novel taxa are
described and imaged or illustrated. Nomenclatural issues and
lectotypification of 15 Chaetanthera names and 6 Oriastrum names
are effected. Chaetanthera is described here with one novel species
(C. pubescens A.M.R. Davies), one novel variety (C. glandulosa var.
microphylla A.M.R. Davies), a new name (C. frayjorgensis A.M.R.
Davies), and three new combinations: C. albiflora (Phil.) A.M.R.
Davies, C. depauperata (Hook. & Arn.) A.M.R. Davies, C.
taltalensis (Cabrera) A.M.R. Davies. Oriastrum is described here
with four new species and one new variety: O. werdermannii A.M.R.
Davies, O. famatinae A.M.R. Davies, O. tarapacensis A.M.R. Davies,
O. tontalensis A.M.R. Davies and O. stuebelii var. cryptum A.M.R.
Davies respectively. Five novel combinations are presented: O.
abbreviatum (Cabrera) A.M.R. Davies, O. achenohirsutum (Tombesi)
A.M.R. Davies, O. apiculatum (J.Rémy) A.M.R. Davies, O. revolutum
(Phil.) A.M.R. Davies and O. stuebelii (Hieron.) A.M.R. Davies var.
stuebelii.