The Hypochaeris sessiliflora complex (Asteraceae, Cichorieae) consists of nine species of the genus from South America (all in section Achyrophorus Scop.) that have sessile or nearly sessile flowering heads surrounded by a rosette of leaves. They occur at 1430–5100 m in elevation along the Andean chain from Venezuela to Chile and Argentina. Two species, H. sessiliflora Kunth and H. meyeniana (Walp.) Benth. & Hook. f. ex Griseb., are extremely polymorphic, and they vary conspicuously in the shape of the external phyllaries and presence or absence of different types of trichomes. They have the widest distributions (Venezuela to central Peru, and Peru to northern Chile and northwestern Argentina, respectively), they flower throughout the year, and they also are primarily associated with dry and sunny habitats. Hypochaeris meyeniana is characterized by retrorsely pinnatifid leaves (rarely lobate) and slightly narrower cypselar apices. Hypochaeris hohenackeri (Sch. Bip.) Domke and H. taraxacoides Ball are glabrous, whereas H. acaulis (J. Rémy) Britton has scattered shaggy trichomes on the leaves; all three occur in humid places, such as seeps or bogs. Hypochaeris eriolaena (Sch. Bip.) Reiche and H. mucida Domke are pubescent, with long whiplike trichomes on leaves and phyllaries, giving a niveous-tomentose appearance. Hypochaeris echegarayi Hieron. (white corollas) and H. eremophila Cabrera (yellow corollas) are two related species with shaggy trichomes on the abaxial surfaces of the phyllaries, both with considerable ecological tolerance, that grow in dry as well as humid sites. Morphological cladistic analyses suggest a hypothesis of relationships within the complex. Surprisingly, H. acaulis from Chile and Argentina, although fitting morphologically within the H. sessiliflora complex, based on amplified fragment length polymorphism (AFLP) data, clearly does not seem to belong to this group. Instead, the species ties to H. palustris (Phil.) De Wild. and H. tenuifolia (Hook. & Arn.) Griseb., also from the southern Andes. The acaulescent habit of H. acaulis seems best interpreted as a parallel adaptation to survival at high elevations.
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Vol. 96 • No. 4