The pollen morphology of Phyllanthus (Euphorbiaceae) section Choretropsis

The pollen grain morphology of the eight South American species of the genus Phyllanthus, subgenus Phyllanthus, section Choretropsis, endemic to Brazil, was investigated using light and scanning electron microscopy. The high homogeneity in pollen shape, as well as aperture number and configuration, allowed the definition of a basic pollen type for this section, viz. prolate spheroidal or subprolate, zonocolporate with 4-5 invaginated colpi, sexine reticulate. Two subtypes have been observed, based on pollen grain apertures and exine sculpture. The first subtype is characterized by straight and narrow colpi provided with costae, lalongate endoapertures and a reticulum of rectilineous muri as in P. choretroides and P. spartioides. The second subtype has wider colpi without costae, circular endoapertures and a reticulum with curvilineous muri as in P. flagelliformis, P. goianensis and P. scoparius, or curvilineous-rectilineous muri as in P. angustissimus, P. gladiatus and P. klotzschianus. It was demonstrated that the pollen shape and the number of colpi varied within and between some of the species. The results suggest that pollen grain morphology, in association with plant architecture and the presence of phylloclades, constitute additional evidence to delimit the species of the section Choretropsis and to further understand their evolutionary origin within the genus Phyllanthus. (C) 2004 The Linnean Society of London.