Interspecific pollen transfer among co-occurring heteromorphic and homomorphic species

Pollen transfer, and hence sharing of pollinators, among Primula veris, Narcissus assoanus, and Potentilla tabemaemontani in Northern Spain is demonstrated in the study of pollen loads on their stigmas. The length of style in both P. veris and N. assoanus is dimorphic (the former being a typical distylous species); they resemble each other in flower morphology (narrow-tubed), color, and nectar characteristics. Therefore, interspecific pollen transfer between these two species shows a pattern related to these similarities. It is inferred that the pattern of interspecific pollen transfer is mediated mainly by long-tongued pollinators seeking nectar, and that of intraspecific pollen transfer by long- and short-tongued pollinators feeding on nectar and pollen, respectively. The floral features of P. tabemaemontani are markedly different, especially in flower architecture (open) and reward (pollen). Accordingly, pollen transfer to other species is reduced, the long-styled flowers of N. assoanus being the exception. This is probably due to frequent visits of pollencollecting insects to the upper stamen whorl of N. assoanus, which therefore would also be a pollen-rewarding species, as has been observed in other similar Narcissus species.