Pollen morphology of Bougainvillea (Nyctaginaceae): A popular ornamental plant of tropical and sub-tropical gardens of the world

Abstract

Bougainvillea (Nyctaginaceae) is a vigorously growing and heavily climbing South American shrub, extensively grown in India, and is favoured for its attractive brightly coloured bracteal flowers. The present communication encompasses the detailed pollen morphometric analysis of Bougainvillea species (B. glabra Choisy, B. peruviana Bonp., B. spectabilis Willd. and B. buttiana Holttum & Standl.) using both light microscope (LM) and field emission scanning electron microscope (FESEM) that may contribute to taxonomic characterization of these species as well as utilize the knowledge of their finer morphology in order to correlate them with 22 Indian varieties belonging to either of the above species. Pollen grain is 3–4-zonicolpate; sub-oblate to spheroidal to prolate-spheroidal; sexine reticulate (muri provided with scattered spinuloid excrescences, lumina baculate) and mostly thicker than nexine. The smallest pollen size is observed in B. glabra var. shweta (22.1×22.7μm), whereas the biggest pollen size is recorded in basal species of B. buttiana (38.6μm in diameter). The pollen grain size of rest of the species and varieties of Bougainvillea falls between these two. The study portrays that the species are in close similarity regarding aperture and exine thickness and could be discriminated through shape, size and sexine ornamentation (particularly distribution of larger and smaller brochi). Besides, the present examination is a maiden attempt regarding the pollen morphometric analysis of basal species of B. peruviana and B. buttiana, along with 21 Indian varieties. The rest of the two basal species (B. glabra and B. spectabilis) and Partha variety of B. peruviana have been discussed scatteredely in earlier reports. Thus, the present observation will be helpful in morphotaxonomy for accurate identification and in turn help in finding same from modern and sub-surface soil in order to study present status of pollen preservation, evolutionary trend and palaeoenvironment of the region, respectively.