EVIDENCE FOR THE HYBRID ORIGIN OF CAREX KNIESKERNII WITH COMMENTS ON HYBRIDIZATION IN THE GENUS CAREX (CYPERACEAE)

Carer knieskernii, originally described as a distinct species, is show n to be a sterile hybrid between Carer arctata and Carer castanea base d on evidence from allozyme variation, chromosome numbers, morphology, and geographical distribution. The two parental species differed at e ight enzyme-coding loci; C knieskernii showed the expected heterozygou s pattern at each of these loci. Individuals of C. knieskernii were hi ghly sterile and the enzyme patterns suggested that they were F, hybri ds formed independently at each location. Chromosome numbers determine d for 27 individuals of C arctara (n = 27, rarely 26) agreed with prev iously published counts. The eight counts of C. castanea (n = 22) diff ered from the one previous count of 2n = 64. Individuals of C kniesker nii from five different populations all had disturbed meiosis with irr egular pairing and ca. 49 chromosomes. A canonical discriminant analys is of morphological data from population samples of the three taxa cle arly separated C arctata and C. castanea, with the individuals of C. k nieskernii having intermediate scores on the first canonical axis. Car er knieskernii is a widespread but rarely occurring hybrid that is fou nd where the ranges of the parental species overlap and the blooming t imes are synchronous. The sterility of this hybrid, the obvious disrup tions of normal meiotic pairing, and the large genetic distance betwee n the parental species based on allozyme variation suggest that althou gh the two species hybridize, they may not be closely related.