Micromorphology of leaf trichomes in Onosma (Boraginaceae) and their systematic relevance in Iran

Abstract

This study provides the first detailed description of leaves and nectar trichome characteristics in Onosma. The indumentum characteristics of 32 Onosma taxa collected from Iran are given in it, as well as the results obtained from LM and SEM investigations. Three groups have been recognized within the genus, relatively in agreement with the infrageneric taxa of Onosma that Boissier had originally described. The obtained results were confirmed by many molecular, palynological and morphological studies. Furthermore, a diagnostic key has been provided according to which the indumentum, accompanied by other morphological evidences, shows distinct boundaries between sections, subsections and species in Onosma. Although there are taxa which cannot be determined solely using trichome morphology, these evidences can be a very useful tool in distinguishing between many of the currently recognized Onosma taxa.