Patterns of seed polymorphism and allozyme variation in the bladder campions, Silene vulgaris and Silene uniflora (Caryophyllaceae)

Abstract

Seed morphology (testa ornamentation and seed shape) and allozyme variation were investigated in three closely related and partially sympatric taxa of Silene in the Nordic region. Within this region, Silene vulgaris is a widespread weed of anthropogenic habitats. The two subspecies of Silene uniflora are restricted to naturally open habitats; ssp. uniflora has a coastal distribution, whereas the Swedish endemic, ssp. petraea, is restricted to limestone habitats on the islands of Öland and Gotland. All three taxa show a seed ornamentation polymorphism, with individuals producing either tubercled or smooth ("armadillo") seeds. Both seed morphology and allozymes show a separation between the two species Silene vulgaris and Silene uniflora and support the present taxonomic treatment of the endemic "petraea" as a subspecies of Silene uniflora. Tubercled seeds predominate in Silene vulgaris and armadillo seeds predominate in Silene uniflora. However, there is considerable between-population variation in seed morph frequencies within taxa. In contrast to the other two taxa, populations of Silene uniflora ssp. petraea consistently show intermediate frequencies of both seed morphs. Silene uniflora ssp. petraea has the lowest between-population component of diversity in both seed shape (18–46%) and allozymes (0.8%) and shows no significant geographic structure in any of the character sets. Both Silene uniflora ssp. uniflora and Silene vulgaris show significant geographic differentiation in allozymes and seed morphology. The highest between-population component of diversity was found in Silene uniflora ssp. uniflora, where 17% of the total allozyme diversity and 39–82% of the seed shape diversity are accounted for by differences between populations. Key words: allozymes, geographic differentiation, diversity, seed shape, elliptic Fourier coefficients, Landmark characters.