Pollen morphology of some related genera of Vernonieae (Asteraceae) and its taxonomic significance

Abstract

Pollen morphology is an important source of information to increase systematic resolution in Asteraceae, especially in Vernonieae. Aiming to investigate if palynological traits give support to Caatinganthus, Strophopappus and Xiphochaeta as separate genera from Stilpnopappus, we used cluster analysis followed by a test of group sharpness. Further, ordination analysis was applied to detect informative pollen traits associated with the revealed groups. The analyses evidenced five groups: (G1) Caatinganthusrubropappus as a single-species group; (G2) species of Stilpnopappus; (G3) Xiphochaetaaquatica as a single-species group; (G4) Strophopappusbicolor, S.glomeratus, S.villosus, S.ferrugineus, S.pohlii and S.speciosus; (G5) Strophopappusbullatus and S.regnelli. The interruption in the middle of the muri in apertural lacunae explains the single-species group Caatinganthusrubropappus. The thickness of sexine, the type of apertures (porate or colporate), and spine dimensions (length, thickness and distance from each other) are the traits explaining differences between species of Stilpnopappus and Strophopappus. Equatorial lacunae give support to Xiphochaetaaquatica as a single-species group, despite the smaller size of pollen grains of this species as compared to the others species analyzed. The differences among pollen morphology give support to Caatinganthus, Stilpnopappus, Strophopappus and Xiphochaeta as genera according to the taxonomic classification currently accepted. The used approach was efficient to reveal individual pollen traits informative to explain the sharp groups, and was an effective alternative to the use of “pollen types”.