Pollen morphology of Pachycereus weberi (Cactaceae): an evaluation of variation in pollen size

Abstract

Pollen morphology within a single plant species has been regarded as a relatively constant trait; it has, thus, been used as a taxonomic character. Numerous palynological studies have described the morphology of pollen from Cactaceae and from other families of plants. There have, however, been few studies of the variation of pollen traits, especially variation of pollen size. Here, we describe the morphology of pollen grains from Pachycereus weberi, paying particular attention to variation of the diameter of the grains. We found that pollen grains from P. weberi are spheroidal, isopolar, and tricolpate, with microperforate and spinulate tectum and visible perine. Pollen diameter is highly variable. Our results show that pollen size must be used carefully as a taxonomic character. Further, we discuss the importance of sample size in descriptive studies of pollen and diverse meiotic abnormalities that may be implied by the high variation of pollen grain size for P. weberi.