Morphometrical analysis of Ceiba Mill. (Bombacoideae, Malvaceae) pollen: a sacred plant of the Mayan (Mesoamerican) civilisation

Ceiba, is a large tree used for ornamental landscaping in tropical regions of the world. It is found in tropical areas, including Mexico, Central America, South America, the Caribbean, West Africa, and Southeast Asia. The present work communicates the detailed pollen morphology of four Ceiba species growing in India including one hybrid, C. speciosa (A.St.-Hil.) Ravenna, C. insignis (Kunth) P. E. Gibbs & Semir, C. x insignis (cross between C. insignis and C. speciosa) and C. pentandra (L.) Gaertn., using Field Emission Scanning Electron Microscope (FESEM), Confocal Laser Scanning Microscope (CLSM) and Light Microscope (LM) to highlight the taxonomic characterization of these species and document finer morphological details to correlate them with other Ceiba spp., growing around the world. Pollen grain is 4-5-colporate, brevicolpate; sub-oblate to prolate-spheroidal to sub-prolate; sexine reticulate (muri provided with scattered spinuloid excrescences, lumina reticolumellate) and mostly thicker than nexine. The multivariate principal component analysis (PCA) was applied on Ceiba and Bombax ceiba to numerical data obtained from pollen morphometry which clearly revealed a significant variation between different genus and species. A pollen key, based on these micromorphological data (especially pollen aperture and size of muri), is also presented for the Ceiba and B. ceiba. The study provides an analogue for precise identification of Ceiba pollen grains recovered in Quaternary and pre-Quaternary sedimentary deposits in India and other tropical and subtropical regions of the world. Besides, pollen preservation, evolutionary trend and palaeoecology are the other important implications of this study.