Pollen morphology of Lactuca L. (s. lat.) (Cichorieae: Asteraceae) from Hindukush, Western Himalayan and Karakorum ranges and its taxonomic significance

Pollen morphology of 15 species of the genus Lactuca L. (s. lat.) of the tribe Cichorieae from the Hindukush, Western Himalayan and Karakorum Ranges was studied using light microscopy and scanning electron microscopy. The pollen morphology of six speciesm viz. L. erostrata Bano & Qaiser, L. glaucifolia Boiss., L. persica Boiss., L. crambifolia (Bunge) Boiss., L. chitralensis (Tuisl.) Ghafoor, Qaiser & Roohi Bano and L. picridiformis Boiss., was never studied before. Pollen were found to be isopolar, spheroidal to oblate-spheroidal, elliptic to rarely circular in equatorial view, hexagonal in polar view, trizonocolporate and echinolophate with 15 lacunae. Morphometric analysis of the pollen characters was conducted using agglomerative cluster analysis with Euclidean distance and Ward's method to compute the dissimilarity matrix, and a dendogram was prepared. Two pollen types, based primarily on the diameter of the polar and equatorial axes of the pollen grain, were recognized. Keys to the pollen types, subtypes and species are provided. The present palynological findings are to a great extent in agreement with the results of recent phylogenetic studies based on molecular evidence. Moreover, both the pollen types are well correlated with the general morphology of the investigated species of the genus Lactuca L. (s. lat) and provide additional micromorphological characters for the delimitation of the species.

Automated summary

This study investigated the pollen morphology of 15 species of the genus Lactuca from the Hindukush, Western Himalayan and Karakorum Ranges using light microscopy and scanning electron microscopy. The results showed that the pollen were isopolar, spheroidal to oblate-spheroidal in shape, with hexagonal polar view and trizonocolporate echinolophate structure. Two pollen types were identified based on the diameter of the polar and equatorial axes. The findings were consistent with recent phylogenetic studies and provided additional micromorphological characters for species delimitation.