Words similar to capitula
Example sentences for: capitula
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According to Bremer and Humphries [ 2 ] , the Artemisia -group is monophyletic and defined by heterogamous-disciform capitula (disk florets usually bisexual and fertile, ray florets pistillate) or homogamous-discoid capitula (disk florets usually bisexual and fertile, ray florets absent), pollen with short or no spines (associated with anemophily), and thick-walled cypselas devoid of ribs (sometimes faint ribs are present in Sphaeromeria and Crossostephium ). All of the Artemisia -group genera contain species that have been variously placed within the taxonomic boundaries of Artemisia s.l.
Seriphidium as a distinct genus along with several small genera from within the boundaries of Artemisia s.l . The more recent, major classifications [ 2 39 49 50 ] have agreed with the segregation of Seriphidium on the basis of discoid-homogamous capitula and recognized the smaller segregate genera as well.
Tridentatae is characterized by discoid-homogamous capitula, with the exception of S. bigelowii , which has occasional heterogamous-disciform capitula of one pistillate ray floret and two perfect disk florets - a character that was previously considered a plesiomorphy or secondary reversal in S. bigelowii [ 2 ] . Based on ITS and chloroplast phylogenies of sect.
The occasional appearance of disciform capitula in S. bigelowii might be explained by introgression of genes or alleles from A. filfolia that control ray expression, a phenomenon observed in discoid Senecio squallidus and radiate S. vulgaris in Europe [ 67 ] . While this is speculative, it is consistent with hypotheses that hybridization and introgression are widespread in sect.
Tridentatae [ 68 ] , and may explain occasional heterogamous disciform capitula in S. bigelowii [ 34 35 ] . However, there may be many genetic and developmental mechanisms that affect ray formation and control floret fertility [ 69 70 ] .
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