El. Vezey et al., PLESIOMORPHIC AND APOMORPHIC POLLEN STRUCTURE CHARACTERISTICS OF ANTHEMIDEAE (ASTEROIDEAE, ASTERACEAE), American journal of botany, 81(5), 1994, pp. 648-657
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.