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.

Agmatoploidy and Symploidy in Rhynchospora cephalotes (L.) Vahl (Cyperaceae).

“…Since the diploid number in that specimen is 2n=17, this trivalent may be suggested to have arisen by chromosome fusion (symploidy, Luceno and Guerra 1996). Heteromorphic trivalents have been found in other Cyperaceae species by processes of agmatoploidy and symploidy (Faulkner 1972, Hoshino 1981, Cayouette and Morisset 1985, 1986a, b, Luceno 1992, 1994, Luceno and Castroviejo 1991. The configuration 8II+lI, observed in the remaining 10% of the cells may be a dissociation of the trivalent.…”

Chromosome studies on the Carex salina complex (Cyperaceae, section Cryptocarpae) in Northeastern North America.

“…This maximum meiotic association for a given individual was designated its "Maximum Affinity Pairing" or MAP. A MAP formula was thus worked out for every plant from which at least nine cells had been analysed at metaphase I (see Cayouette and Morisset 1985, for more details).…”

“…The objectives of the present study were to determine the chromosome numbers and describe the meiotic behaviour of the three members of the Carex salina complex in northeastern North America. Other papers (Cayouette andMorisset 1985, 1986) will examine relationships between those three species and other related maritime species such as C. paleacea Wahl., C. aquatilis Wahl., and C. nigra (L.) Reichard, and will also present the cytology of natural hybrids between many of the species involved in that complex. Cytologia 51…”

Chromosome Evolution in Cyperales

“…Nuclear irradiation studies (de Castro et al 1949;LaCour 1953;Håkansson 1954;Davies 1956) indicate that chromosome fragments maintain centromeric activity and are not lost during cell division (Lima-de-Faria 1949). Furthermore, hybrids between plants with different numbers of chromosomes reveal one large chromosome pairing with two small chromosomes (Wahl 1940;Tanaka 1949;Håkansson 1954;Davies 1955;Faulkner 1972;Schmid 1982;Cayouette andMorisset 1985, 1986;Hoshino et al 1993Hoshino et al , 1994Hoshino and Okamura 1994). Complicating the picture in hybrids from natural populations is the presence of various univalent and multivalent formations suggesting chromosomal structural rearrangements are involved (Tanaka 1949;Faulkner 1973;Schmid 1982;Cayouette and Morissett 1986;Hoshino and Waterway 1994).…”