Chromosome studies on natural hybrids between maritime species of Carex (sections Phacocystis and Cryptocarpae) in northeastern North America, and their taxonomic implications

Abstract

Morphological descriptions, chromosome numbers, and meiotic behaviour are presented for nine different hybrids of Carex in sections Cryptocarpae and Phacocystis from northeastern North America, mainly salt-marsh species from the St. Lawrence estuary and gulf. They are C. aquatilis × subspathacea (2n = 79), C. nigra × subspathacea (2n = 81, 83), C. nigra × salina (2n = 80), C. paleacea × salina (2n = ca. 74, 75), C. aquatilis × recta (2n = 74), C. nigra × recta (2n = 78, 79), C. paleacea × recta (2n = 73), C. aquatilis × paleacea (2n = 74), and C. nigra × paleacea (2n = 78 + fragment, 79). Hybrids showed a mixture of morphological characters from both putative parent species, and chromosome numbers were mostly intermediate between those of their parents. Meiosis of hybrids was disturbed with variable numbers of univalents, trivalents, and quadrivalents, such as in two of the parent species, C. salina and C. recta. In general, hybrids differed from parent species by the frequent occurrence of desynaptic bivalents and higher numbers of trivalents. Pollen stainability was low in hybrids (10.0–56.6%, with two exceptionally high values of 71.8 and 92.2%). Pollen stainability was also low though quite variable in C. salina (23.7–62.8%) and C. recta (16.2–80.7%), but it was much higher in C. paleacea (92.7–100%), C. nigra (63.1–92.9%), and C. aquatilis (78.0–97.2%). Almost all hybrids and parents produced some well-formed achenes. A formula indicating the maximum affinity pairing (MAP formula) and two euploidy indexes were used to compare hybrid individuals and their parent species. Carex salina and C. recta are cytologically considered of hybrid origin, but they behave ecologically as stable species.