Floral Morphology and a Reassessment of Affinities in the Cotuleae (Asteraceae)

Floral morphology of representatives of the 12 genera that have at some time been assigned to the informal group 'Cotuleae' of the tribe Anthemideae was re-examined. Consistent differences among genera occur in anther and disc style morphology and type and distribution of corolla trichomes. While the ray corolla is greatly reduced in most members, there is still useful variation in its form. A distinctive biseriate corolla trichome capped by an acellular vesicle is described in Centipeda, Cotula, Leptinella, Nananthea, Soliva and Plagiocheilus; it is also widespread in northern hemisphere Anthemideae. Developmental studies in Tanacetum parthenium indicate that the vesicle forms by the separation of the cuticle from the outer cell walls. The data reinforce the conclusion that only Cotula, Leptinella, Nananthea and Saliva belong in the Anthemideae. Dimorphocoma, Elachanthus, and Plagiocheilus belong in the Astereae, the first two close to Minuria, the last near Solenogyne. Isoetopsis belongs in the subtribe Angianthinae of the Gnaphalieae sensu Anderberg, as does Chondropyxis, a monotypic genus that has been linked with Elachanthus and Isoetopsis. Centipeda appears to belong to neither the Gnaphalieae nor the Inuleae sensu Anderberg. Abrotanella and Ischnea are not closely related and, although Abrotanella may belong in the Scenecioneae, it is not a member of the subtribe Blennospermatinae. The affinities of Ceratogyne remain obscure.