Evolution and maintenance of stigma-height dimorphism in Narcissus. I. Floral variation and style-morph ratios

An unusual stylar dimorphism occurs in Narcissus, a plant genus of insect-p ollinated Mediterranean geophytes. To determine the characteristics of the sexual polymorphism, we investigated floral variation in 46 populations of N. assoanus (section Jonquillae) and 21 populations of N. dubius (section T azettae) in SW France. Flowers possess two stamen levels in each morph that occupy slightly different positions within the floral tube. In long-styled plants (L-morph), the stigma is located within or slightly above the upper -level stamens, whereas in short-styled plants (S-morph) the stigma is plac ed well below the lower-level stamens. The stigma-height dimorphism is dist inct from heterostyly because the reciprocity of stigma and anther position s in the two style morphs is only weakly developed and there are no differe nces between the style morphs in pollen size or production. In both species , mean stigma-anther separation is much greater in the S-morph than the L-m orph. In N. assoanus, population style-morph ratios vary from isoplethy (1L :1S) to L-biased, whereas in N. dubius they are usually strongly L-biased o r occasionally contain only the L-morph. Populations fixed for the S-morph, or with S-biased morph ratios, were not observed. In N. assoanus, style-mo rph ratios were associated with population size: large continuous populatio ns always exhibited 1:1 morph ratios, whereas smaller, fragmented populatio ns were often L-biased. This pattern was not evident in N. dubius. We argue that biased style-morph ratios largely result from morph-specific differen ces in assortative mating.