Pollen morphological investigations of family Cactaceae and its taxonomic implication by light microscopy and scanning electron microscopy

Abstract

The family Cactaceae is the diversified group of angiosperm plants whose pollen statistics has been used for taxonomic identification. In this article, we present the pollen morphology of eight species belong to seven taxonomically complex genera of Cactaceae includingAstrophytum,Cylindropuntia,Echinocereus,Echinopsis,Mammillaria,Opuntia, andThelocactususing light and scanning electron microscopy. The pollen grains were acetolyzed, measured, described, and electron photomicrographs were taken. Cactaceae can be characterized by presenting different palynomorphological features including pollen type, sculpturing, polar and equatorial diameter, aperture orientation, exine thickness,P/Eratio, and echini features. Four types of pollen shapes, that is, prolate spheroidal (three species), subprolate (two species), prolate (two species), and oblate spheroidal inEchinocereus reichenbachiiwere observed. The polar and equatorial diameter observed maximum inO.ficus indica116.95 and 112.27 mu m while minimum inM.compressa38.42 and 21.05 mu m. Pollen of two types, tricolpate in members of subfamily Cactioideae and pantoporate in the Opuntioideae were examined. The fertility percentage has been observed maximum inOpuntia macrocentra(83.84%) and minimum inOpuntia ficus-indica(57.89%). Exine sculpturing showing great variations such as granulate, reticulate, granulate perforate and micro-echinate foveolate ornamentation was examined only inEchinopsis eyriesii. A key to species, based on pollen micromorphological attributes, has been constructed for correct identification of complex cactus species.