Systematics value of micromorphological and palynological characters in stenocephalum sch.Bip. (vernonieae, asteraceae)

Abstract

Micromorphological and palynological characters of all Stenocephalum Sch.Bip. species (Vernonieae, Asteraceae) were analyzed to evaluate their reliability as taxonomic markers at generic level and discussed in relation to other genera of the subtribe Lepidaploinae. Characters such as pubescence of corollas and cypselae showed glandular and nonglandular trichomes allowing differentiation among related species. Apical appendages without glandular trichomes, caudate anthers, and carpopodium structure are common characteristics among Stenocephalum species. With the exceptions of S. megapotamicum and S. tragiaefolium, almost all species of the genus showed style bases without basal nodes for the first time. Crystals on the fruits wall were also observed for the first time in almost all the Stenocephalum species, with the exception of S. hystrix. However, the crystals would not constitute diagnostic features, since they vary widely among species. All the species showed type C pollen and the genus is considered stenopalynous. However, highly significant differences in palynological features among the species of the genus were observed. The different combinations of the micromorphological and palynological features of Stenocephalum here analyzed are valuable within genera to differentiate related species from one another. The value of all these characters could be increased if they are combined with other morphological or traditional data.