PLESIOMORPHIC AND APOMORPHIC POLLEN STRUCTURE CHARACTERISTICS OF ANTHEMIDEAE (ASTEROIDEAE, ASTERACEAE)

Anthemideae (Asteroideae: Asteraceae) pollen grains have basal columel lae, a structural type called ''anthemoid'' in earlier publications. T o survey structure variation in Anthemideae pollen, we examined freeze -sectioned grains from 45 species within 23 representative genera usin g scanning electron microscopy (SEM). From resulting data and a litera ture review, we concluded that: 1) pollen of Anthemideae taxa is quali tatively identical except for Ursinia (grains essentially lack basal c olumellae) and the Artemisia group (branches of basal columellae are c omplex and interwoven); 2) the double tectum (a term introduced in thi s study) is a synapomorphy of Asteroideae and plesiomorphic in Anthemi deae; 3) apomorphies of Anthemideae grains include large basal columel lae, a thick foot layer, and absence of internal foramina; and 4) Anth emideae pollen is qualitatively different from similar pollen in Lactu coideae, a distinction we recognized by restricting ''anthemoid'' to A nthemideae grains. Ursinia grains have occasional basal columellae and features resembling rolled-up columellae; we consider these vestiges of a reversal to the plesiomorphic condition. To assess quantitative s tructural variation, 2,200 image-analysis measurements were taken from 73 SEM micrographs. Intrageneric variation was analyzed by standard d eviation, and intergeneric variation by principal components analysis. Compared to other Anthemideae taxa, the structural elements of Artemi sia grains have reduced dimensions and variability. Otherwise, structu ral radiation of Anthemideae pollen has produced a phenetic continuum.