Morphology, Anatomy, and Taxonomic Relationships of Otopappus australis (Asteraceae)

Abstract

A collection of Otopappus australis from Cerro Campana represents the first report for the genus from Panama. Aspects of the morphology at variance with the type description include longer and narrower leaves and narrower flowering heads. Details of stem and leaf anatomy are reported; exceptionally tall primary wood rays probably relate to the plant's vine-like habit. A variety of primitive and specialized features are found in the floral anatomy. Unusual topographic sites for trichomes include pappus awns, inside the corolla tube, anther appendages, and style branches. The junior authors conclude that this species is more properly a Zexmenia rather than an Otopappus. Geographical and morphological data are uti- lized to demonstrate that 0. australis, Z. columbiana, and Z. mikanjoides are conspecific. The latter two are considered Zexmenia mikanioides var. mikanioides, and the nomen- clatural combination is made to make 0. australis a variety of Z. mikanioides. The genus Otopappus Benth. belongs to the subtribe Verbesininae of the Heliantheae (Asteraceae) and contains about 15 species as presently understood (Hartman and Stuessy, unpubl.). Most taxa are found from western Mexico to Costa Rica. The closest generic relatives are Notoptera Urb. and Salmea DC. (Blake, 1915a; Stuessy, 1977). McVaugh (1972) suggested that the generic distinctiveness of Otopap- pus and Notoptera may be specious and recent revisionary studies (Hart- man and Stuessy, in prep.) have shown that the taxa are congeneric. The genus is unified by its viny habit and winged awns of the achenes. How- ever, one species, 0. australis, is isolated morphologically and geograph- ically. This taxon was originally described by Blake (1924) as a relative of 0. verbesinioides Benth. and as the first representative of the genus from South America. Features of the achenes of 0. australis differ from other species of the genus and suggest possible affinities with other gen- era. Geographically, 0. australis is known from Venezuela and Ecuador, which are outside the known range of all other species of the genus (0. simplex Badillo was also described from Venezuela, but it does not belong in Otopappus; details of that relationship will be described elsewhere). Interest in Otopappus australis has developed independently with the senior author finding material new to Panama, and the junior authors determining specific and generic relationships. Discovery of each other's work suggested that the observations and interpretations be published