Pollen morphology of the genus Lamium L. (Lamiaceae) and its systematic implications

Abstract

This is the first comprehensive palynological investigation of the genus Lamium. The pollen morphology of 48 taxa (including species, subspecies and varieties) of the genus Lamium was investigated and documented using light microscopy (LM) and scanning electron microscopy (SEM). Lamium pollen is small to medium sized (P = 21.65-39.96 μm), oblate-spheroidal to subprolate in shape and tricolpate. Three major exine sculpturing patterns (reticulate, granulate and microreticulate) were observed. The results indicated that the exine sculpturing pattern of Lamium is systematically informative at sectional level, but not at the species and infraspecific levels. In the present study, the palynological data are compared with available phylogenetic studies to evaluate the systematic value of pollen characters in the genus. Analysis show that; (1) Mennema's infrageneric classification is partly corroborated by our palynological data, (2) recent phylogenetic analysis on the genus and our results are partly corroborated, and (3) pollen morphology supports the inclusion of L. galeobdolon (=Galeobdolon), L. orientale and L. multifidum (=Wiedemannia) in Lamium. (4) Variation in exine sculpturing pattern have systematic importance particularly at sectional level.