Morphological and morphometrical pollen analy- sis of Corchorus, Heliocarpus, Luehea, Mollia and Triumfetta (Malvaceae, Grewioideae) in southern South America

Abstract

Although Grewioideae is known as the only stenopalynous subfamily of Malvaceae, previous published pollen analyses suggest morphological variation. To test if that structural variation could have taxonomic value, pollen morphology of 16 species of the genera Corchorus, Heliocarpu, Luehea, Mollia and Triumfett (Malvacea, Grewioideae) distributed in southern South America was analysed by light and scanning electron microscopy. Pollen grains are 3-zonocolporate, isopolar, radially symmetrical, subspheroidal to prolate, and medium to large in size. Exine sculpture varies from a bireticulate reticulum with perforated lumina to densely tectate-rugulate or tectate-microreticulate. Pollen morphological characteristics from light microscopy were used in a multivariate analysis to assess variation within and among the genera. Principal components analyses (PCA) clearly separate five groups based on pollen shape and size, colpus length, endoaperture height and width, and exine thickness. The species here studied share the Grewia pollen type, like most species of Grewioideae and Byttnerioideae, but the palynological characters analyzed have little taxonomic value at genus or species level.