A pollen morphological survey of the Old World species ofStenandriumNees (Acanthaceae: Acantheae)

Abstract

Abstract The pollen of fourteen species of Stenandrium Nees from Africa and Madagascar has been examined using light microscopy, scanning electron microscopy and selectively with transmission electron microscopy. The pollen exhibits an interesting range of variation. Four pollen types are described. Pollen Type I is usually prolate, tricolpate and has colpi without margines. In one collection of Stenandrium humile (Mabberley 995) irregular 4–6-colpatc grains occur. Pollen Type II is oblate spheroidal to prolate spheroidal, 3–6-colpate with irregular apertures. Pollen Type III is perprolate, tricolpate and the colpi have prominent margines. Abnormally-shaped grains were found in one collection of Stenandrium afromontanum (Lovett & Congdon 3068). Pollen Type IV is prolate to perprolatc, tricolpate with prominent margines and mesocolpial ridges. Because of the high level of abnormality encountered, material from each species, according to availability, was tested for the presence or absence of cytoplasmic contents. Pollen lacking cytoplasm was found in several collections. The reasons for this and for the presence of irregular pollen grains are not known at present, although chromosomal abnormalities are suggested as a possible cause. The pollen morphology is discussed in relation to the sectional classification of Vollesen and with respect to relationships within the Acantheae. In particular, a close relationship with Crossandra Salisbury is suggested. The results of a brief survey of the pollen morphology of selected Stenandrium species from South America are discussed.