Pollen diversity in the genus Ptilostemon (Asteraceae, Cardueae) from Italy and its taxonomic and palynoecological implications.

The results of a study on pollen morphology of the species of the genusPtilostemongrowing in Italy:Ptilostemon niveus, P. greuteri,P. gnaphaloides,P. casabonae,P. strictus,P. stellatusby light and scanning electron microscopy were presented and discussed including in relation to their taxonomic position. The exine shows two different ornamentation patterns: echinae and scabrae. This last ornamentation pattern together with other features was previously described in the genusPtilostemon. Of 6 species analysed,P. stellatusis the only one that shows a scabrate ornamentation of exine. Two pollen types were recognized through the exine ornamentation, length of ectocolpus and polar outline:P. stellatustype andP. niveustype. A multivariate analysis (principal component analysis and linear discriminant analysis) was carried out with the aim of examining potential morphological characters which could be used to identify taxa. The data suggest that several characteristics can be used to delimit the species in particular the exine ornamentation. The results of our studies support the actually subgeneric classification, and several features of the pollen grains analysed seem to have a palynoecological role and an important taxonomic significance. A dichotomous key based on palynological data is also given. [ABSTRACT FROM PUBLISHER]