High phenotypic variation of Struthiopteris spicant (Blechnaceae) at the edge of its range

Abstract

Phenotypic variation may be due to genetic and/or environmental causes. Many ecologists consider that phenotypic plasticity, which is the change in the phenotype expressed by a single genotype subjected to different environments, is an evolutionary strategy for adapting to variable environments. Also, it has been hypothesized that plasticity is higher in peripheral populations. Struthiopteris spicant is widely distributed in Europe and also in Pacific North America. It has two varieties in Europe (var. homophyllum and var. pradae), which varies in the type and degree of dimorphism. In this work we contribute new locations which extend their known distribution in mainland Europe as well as in some Macaronesian islands. The specimens found are mixed with individuals of var. spicant and individuals with intermediate phenotype between this variety and the other variety present there. Our data gives some support to the hypothesis of increased phenotypic plasticity in edge populations. In addition, our data seems to follow the pattern which states that there is an association between frond dimorphism and resource-rich habitat, since the monomorphic phenotype tend to appear in slopes with skeletal soils, where the nutrient availability is lower than in forest understories, the typical habitat of var. spicant.