Pollen morphological variation of Primula merrilliana and its systematic significance

Abstract

Primula merrilliana is a distylous, rare, vulnerable herb and of high value in horticulture. Previous studies indicated that the genetic differentiation among populations of this species was remarkably greater than that of its closely related species, suggesting that it may not be a single homogeneous species. In order to further explore the natural variation and identity of the species, pollen morphology and ITS DNA sequences of 18 populations covering its whole distribution were investigated. According to the pollen shape and aperture type, P. merilliana has two different pollen types; six populations from the northwest corner of the distribution area have stephanocolpate and suboblate pollen grains, while the remaining 12 populations possess pantoporate and spherical pollen grains. The mean genetic distance among populations with the same pollen type (mean 0.009) was significantly lower than that of populations with different pollen types (mean 0.023). Pollen morphological characteristics of P. merrilliana have taxonomic value for species identification, suggesting that P. merrilliana is a species complex that comprises two different species. Pollen size variations support the hypothesis that Fenghuangshan (FHS) and Dongshan (DSC) populations, having both sexual organs at the mouth of corolla tube, are long-homostyled populations (not a phenotype with stamen modification of a long-styled morph), while the Qidu (QD) population, having both sexual organs at the middle of the corolla tube, is a short-homostyled population (i.e. not a stamen modification of a short-styled morph).