Nutlet micromorphology and its taxonomic utility in Lamium L. (Lamiaceae)

Abstract

This paper presents results of examination of fruit surface in the genus Lamium L. (Lamiaceae) using scanning electron microscopy (SEM). The purpose of this study was to define new features that differentiate taxa difficult to identify on the basis of macromorphological features, such as species of hybrid origin and subspecies within Lamium. The results of our research show that the SEM analysis of fruit surface allowed defining new diagnostic features for almost all studied representatives of the genus Lamium except for L. confertum from L. coutinhoi and L. album subsp. album from L. album subsp. barbatum. The most useful feature in distinguishing the examined species was cuticle striation. I turn, the type of secondary sculpturing of the cell walls divided the species studied into two main groups. One of them consisted of four taxa (L. album, L flexuosum, L. garganicum, L. orvala) with thickenings of the cell walls in the form of irregular ridges and tubercles. The other one comprised all the remaining species, with cell wall thickenings forming regular papillae. The only species which could not be qualified to any of these groups was L. moschatum. The obtained results demonstrated also high similarity of L. galeobdolon to the remaining species of Lamium, especially L. flexuosum and L. orvala. This observation provides an argument for the inclusion of L. galeobdolon to the genus Lamium.