Developmental variation in a species of Isoglossa (Acanthaceae: Ruellioideae) over a season

Abstract

In his appraisal of Isoglossa Oerst., Clarke (1901) placed major emphasis on the sizes of leaves and inflorescences in the key to species, but efforts to sort herbarium material have shown a great deal of variation in leaf size and inflorescence length that is very difficult to interpret. Specimens of a species of Isoglossa were collected from wild subpopulations from the Hartebeespoort Dam and Hartebeeshoek areas, at intervals over a season. Leaves and inflorescences were measured, and frequencies of hair types on bracts and calyces were recorded photographically Results indicate that leaf size within a species increases over the vegetative phase of the plant and that inflorescence size within a species increases over the reproductive phase of the plant. Therefore, caution should be applied when these characters are used for species identification in Isoglossa. Bract and calyx indumenta also change over a season, thus making it necessary to use wisdom when applying this character taxonomically.