Evolution in sedges (Carex, Cyperaceae)

Abstract

Carex is the largest and most widespread genus of Cyperaceae, but evolutionary relationships within it are poorly understood. Subgenus Primocarex was generally thought to be artificial and derived from diverse multispicate species. Relationships of rachilla-bearing species of subgenus Primocarex, however, were disputed, with some authors suggesting derivation from other genera, and others believing them to be primitive. Subgenus Indocarex, with compounded inflorescence units, was thought to be primitive, with subgenera Carex and Vignea reduced and derived. However, occurrence of rachillas is not confined to a few unispicate species, as previously thought, but is widespread. The often suggested connection between Uncinia and unispicate Carex is shown, based on rachilla morphology, to be founded on incorrect interpretation of homology. Uncinia kingii, the alleged connecting link, is, in fact, a Carex. Unispicate Carex without close multispicate relatives probably originated from independent, ancient reductions of primitive, rachilla-bearing, multispicate Carex. The highly compounded inflorescences occurring in subgenus Vignea are hypothesized to represent a primitive state in Carex, and the more specialized inflorescences in subgenus Carex derived from inflorescences of this type. The relationships of subgenus Indocarex, with its unique perigynium-like inflorescence prophylls, remain unclear.

Chromosome Evolution in Cyperales

“…An ideal system to study this process-both at a larger scale and at the finer level of chromosome fission/fusion-is provided by the genus Carex in Cyperaceae. The genus has the most extensively developed aneuploid series of any angiosperm genus and is one of the largest genera in the world, with approximately 2000 species (Reznicek 1990). Chromosome numbers range from n ϭ 6 to 68 (Davies 1956;Nishikawa et al 1984), with nearly every haploid number between the two extremes present in the genus (Davies 1956).…”

Pollen size inCarex: The effect of different chemical treatments and mounting media

“…Carex is the largest and most widespread genus in the sedge family, Cyperaceae (Reznicek, 1990). Of some 2 000 species recognised worldwide (Chater, 1980;Egorova, 1999), about 70 are found in Estonia (Krall et al, 1999;Kuusk et al, 2003).…”

Numerical variations in species exhibiting holocentric chromosomes: a nomenclatural proposal

“…Additionally, REzNICEK (1990) concluded in his review of evolutionary tendencies in the genus Carex that many cases of chromosomal evolution, which HEILBORN (1924), WAHL (1940) and others attributed to fission, could be better understood as having originated by «aggregation». This would explain why low chromosome numbers are found in species of the section Acrocystis Dumort., which have highly specialized inflorescences and are considered to be advanced.…”

“…This is reflected by heteromorphic trivalents at meiosis in fusion or fission heterozygotes, where one large chromosome in central position is flanked by one medium-sized and one small chromosome (HosHINo 1981;LuCENO 1992). REzNicEK (1990) argued that the «aggregations» in Carex could «he associated with fixing of favorable allelic combinations related to migration into specialized habitats». The same argument was employed by STEBBINS (1971) to explain the evolution of highly asymmetric karyotypes.…”