Taxonomic studies in Acanthaceae: testa microsculpturing in southern African species of Thunbergia

Abstract

A literature survey has shown that seed surface patterns (seedscapes) are taxonomically valuable in the Acanthaceae. Seed surfaces of 11 southern African species of the genus Thunbergia Retz. were investigated using light and scanning electron microscopy. The aims were to establish whether testa surface patterns are constant within species, are speciesspecific and can be used for species identification and circumscription. Results showed that testa surface patterns have value in identifying species, but that some features show infraspecific variation. It has been questioned whether T. atriplicifolia E. Mey. ex Nees is a single entity, since there is a wide range of morphological variation in this species. Testa surface patterns are similarly variable. A number of forms, some of which correspond to previously recognized taxa, now subsumed under T. atriplicifolia, were investigated. On their own, features of the testa do not provide grounds for subdividing T. atriplicifolia into separate taxa or for the recognition of T. galpinii Lindau. This complex requires further detailed morphological investigation.