Researchers from Estonia and Switzerland studied regional morphological differentiation of two closely related hybridising (and “taxonomically difficult”) species – Carex flava and Carex viridula. We asked whether due to genetic admixing of the two species within regions, variation between species within regions may be small and variation within species between regions similar between the two. 

Alternatively, as one of the studied species, C. flava, is more common and the other, C. viridula, has more of a patchy distribution and smaller populations, regional differentiation could be more pronounced in C. viridula.

Carex flava

We show that, despite their admixing, the two closely related Carex species differ in their regional morphological differentiation, which was less pronounced in the more common species. The study implies that understanding morphological variation of hybridising species requires addressing variation for large geographic areas.

In addition, our study clarifies the morphological differences between the two species, which are considered as notoriously difficult to distinguish.

Citation: Schmidt, L., Fischer, M., Schmid, B., & Oja, T. Despite admixing two closely related Carex species differ in their regional morphological differentiation. Plant Systematics and Evolution, DOI 10.1007/s00606-017-1420-0 (link to full text)

Carex viridula

Abstract:

Rarer species are expected to show stronger geographic differentiation than more common species. However, if rare species hybridize with common species, differentiation may be quite similar between the two due to genetic admixing via backcrossing. We studied morphological differentiation of plants of 21 natural populations of the more common Carex flava, 16 of the less common Carex viridula and 6 of their hybrids from 27 sites in three climatically different regions, Estonia, Lowland Switzerland and Highland Switzerland. Univariate ANOVA and multivariate principal component analysis of 14 morphological characters, describing both vegetative and reproductive characters, allowed to clearly distinguish C. flava from C. viridula. Carex viridula populations showed stronger regional variation than C. flava. Hybrids had both intermediate and transgressive characters in Switzerland and Estonia. On average, hybrids from Lowland Switzerland were more similar to Swiss C. flava than to C. viridula, while hybrids from Estonia were morphologically intermediate between plants of Estonian populations of the parental species. The results suggest that within-region genetic admixing between species has limited potential to lead to region-specific similarity between species, at least in our model system of the C. flava complex. We conclude that C. flava and C. viridula are clearly distinct species and that, despite hybridization, geographic differentiation is more pronounced in the less common C. viridula than in C. flava.