Pollen studies in the genus Echinops L. and Xeranthemum group (Asteraceae)

The phylogeny of the genus Echinops and the Xeranthemum complex were the subject of a previous molecular study of the tribe Cardueae. An electronic microscope survey of pollen morphology and ultrastructure is presented for all the genera belonging to these groups, allowing four pollen types to be identified. The exine pattern indicates that there are two pollen types in the genus Echinops (including Acantholepis ), although no differences have been found between sections in Echinops . First, the annual species of Echinops and Acantholepis orientalis show a pollen type that differs from that of perennial species of the former genus and, second, the genera Chardinia and Xeranthemum exhibit a pollen type distinct from that Amphoricarpos and Siebera . The internal structure of the pollen wall is the same for all the genera. Only slight differences were observed in the tectum, but in all cases these were of the anthemoid type. Statistically significant correlations between pollen size and the life cycle were found. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 549–557.