Genetic Differentiation of Carex flava and Carex viridula in West Europe (Cyperaceae)

Abstract

Recent systematic treatments evaluating variation in the Carex flava species complex have divided the West European representatives into two species, C. flava and C. viridula. These treatments contrast with previous reports that have recognized as many as nine species based upon morphological variation. To assess the systematic relationship of C. flava and C. viridula, allozyme analyses were conducted on 34 West European populations distributed from the Alps to the Arctic Circle. Data were obtained from electrophoresis of soluble enzymatic proteins extracted from leaf tissue. Fifteen of the 20 presumptive loci examined for this study were found to be polymorphic; variation was distributed between the two species and within 25 populations. These data support recognition of C. flava as a species distinct from C. viridula at a genetic identity of 0.69. The two species are discriminated by diagnostic alleles at two loci and highly disparate allele frequencies at an additional five loci. There is little genetic differentiation among populations of C. flava in West Europe. Genetic identities exceeding 0.95, which were obtained from infraspecific pairwise comparisons of C. flava, do not support recognition of subspecies. In contrast, C. viridula was highly differentiated with a GST of 0.806 strongly supporting recognition of subspecies. The Carex flava L. species complex is one of the most complicated, yet well-studied groups of sedges in Europe. It is included within sect. Ceratocystis Dumort., which comprises seven species worldwide (Crins and Ball 1988). The literature on the C. flava complex contains numerous reports on its morphology, e.g., Crins and Ball (1989a); regional distribution, e.g., Havlkkova (1983); ecology, e.g., Schmid (1984a, 1984b); nomenclature, e.g., Schmid (1983); floral biology and flowering phenology, e.g., Vonk (1979); karyotype and crossability, e.g., Schmid (1982); taxonomy, e.g., Crins and Ball (1989b); and evolution, e.g., Crins and Ball (1988). Schmid (1982, 1983, 1984a, 1984b), in a series of publications considering the European representatives of this group, reported on the ecology, systematics, and evolution of the Carex flava complex. Schmid's treatment divided the complex into two species, C. flava and C. viridula Michaux, recognizing five subspecies comprising C. viridula. Crins and Ball (1989b) also recognized two species in the European flora, but acknowledged less subspecific variation meriting taxonomic status in C. viridula. Starch gel electrophoresis and allozyme analysis are powerful tools for elucidating systematic relationships in Carex (Bruederle and Fairbrothers 1986; Ford and Ball 1989; Waterway 1988; Whitkus 1985). Allozyme data have been useful in discriminating morphologically cryptic taxa, e.g., C. crinita var. brevicrinis Fern. (Bruederle and Fairbrothers 1986), as well as confirming the taxonomic status of taxa, e.g., C. mitchelliana M. A. Curtis (Bruederle et al. 1989). We report here on detected allozyme variation within the C. flava species complex in West Europe. The purpose of this publication is twofold: 1) to present electrophoretic data assessing variation within the complex and discuss the systematic relationship of the two widely recognized species C. flava and C. viridula; and 2) to consider the distribution of infraspecific variation within each of these two species and briefly evaluate subspecific relationships. MATERIALS AND METHODS Plants were collected at 23 sites distributed from Switzerland and Austria to northern Norway (fig. 1; table 1). Whereas 20 to 50 individuals were collected from large populations, a complete sample of all observed individuals was obtained from populations comprising fewer than 20 individuals. The caespitose habit of the species facilitated recognition and collection of individuals for the study. Plants were cultivated and maintained in a common garden or glass