Hybridization in the genusCarex with special reference to North America

Abstract

The first reports ofCarex hybrids in North America appeared in the middle and late 1800’s. By the early 1900’s and up to the middle 1900’s there was disagreement among the influential North American botanists regarding the extent to which hybrids existed. Those who recognized hybridization inCarex have been largely supported by recent studies, but only a small proportion of the reported hybrids are well documented. An understanding of hybridization in the genus is very important to systematic research and routine identification, as well as to the study of evolution and ecology. A total of 253Carex hybrids have been reported from North America, the greatest number of hybrids occurring in the northeast, where recent glaciation and overlapping flowering periods are probably among the causal factors. Based on current reports, hybrids are much more prevalent in subgenusCarex than in subgenusVignea. Field studies and cultivation have proven useful in determining hybrid parentage and delimiting morphological variation, respectively. Both reproductive and vegetative characters as well as anatomical and micromorphological characters have proven taxonomically useful. Cytological studies have documented meiotic irregularities inCarex hybrids and intermediate chromosome numbers. Variation in the meiotic anomalies is apparently associated with the relationship of the parents and with differences in chromosome number.Carex hybrids are largely sterile but some restoration of fertility is evident in backcrosses. Experimental hybridization, flavonoid chromatography, enzyme electrophoresis, phenological characteristics, developmental anomalies and host-parasite relationships have all been underexploited in the characterization of hybrids. A cross-referenced list of North AmericanCarex hybrids is included, along with a list of hybrids not yet reported for North America involving circumpolar species.