AbstractPrimula merrilliana, a rare and endangered National Grade Ⅲ protected plant, is endemic to Anhui Province, China. We studied its reproductive characteristics from the aspects of phenology, breeding system structure and pollination. Our observations showed that: (1) P. merrilliana is typically distylous in both mor-phology and function, and it is a biennial plant that grows from September in the first year and lasts until late June or early July of the next year. In addition, the long-styled plants tend to flower 3 to 5 days earlier than the short-styled morphs in each population; (2) The pantoporate pollen of P. merrilliana shows that the spe-cies has vital taxonomical and evolutionary significance in Primula. The short-styled pollen diameter is 1.78 times as wide as the long-styled, but the pollen production of a short-styled flower is less than that of a long-styled flower; (3) The long-styled pistil is about 1.64 times as long as that of the short-styled morph with shorter and more frequent papillae; (4) The pollen-ovule ratio (P/O) is different in the three studied populations, and we noted larger variation in pollen than ovule production, which may be related to habitats; (5) P. merrilliana is an outcrossing plant pollinated by thrips, and the seed-set of legitimate pollination is higher than that of illegitimate; and (6) The seed morphology of P. merrilliana usually appears like a non-equilateral heptahedron, a few seeds resembles an irregular polyhedron, but there is no obvious difference between the two morphs, the long-styled and the short-styled. Based on this study, biased morph frequencies in small populations of P. merrilliana, destruction of habitats and disappearance of accompanying species are possibly the main reasons for the endangerment of this species.