The genus Salsola (Chenopodiaceae) in southern Africa: Systematic significance of leaf anatomy

Abstract

Almost 90 species of Salsola L. are believed to occur in southern Africa. Correct identification of the different species is, however, rendered problematic by the great morphological similarity of almost all the species, uncertainties concerning the specific status of several entities and the unsatisfactory infrageneric classification of the group. A comparative anatomical study of the leaves of southern African Salsola species was conducted using LM and SEM techniques. The leaf anatomy of southern African Salsola species shows a variation on the typical Salsoloid-type Kranz-anatomy, in that the palisade mesophyll and bundle sheath are not continuous around the leaf, but only present abaxially. Leaf anatomy, particularly the structure of the leaf in transverse section and the type of the indumentum, proved to be very useful for delimiting groups within the genus. The investigated species can be primarily divided into two main groups, according to the presence or absence of a uniseriate adaxial hypodermis. A secondary division can be made by using four main indumentum types, based on the appearance of the abaxial leaf surface. Species possessing one indumentum type can be further subdivided according to the area of the leaf covered by trichomes and the number of elongated cells in the trichomes. There is a weak association between leaf type and hitherto proposed subsections, as well as between leaf type and indumentum type. In general species possessing an adaxial hypodermis tend to have a denser indumentum than species lacking one.