Estudo citogenético e evolutivo em espécies brasileiras de Eleocharis (Cyperaceae)

A karyotype analysis of 147 populations of 25 Brazilian species of Eleocharis (Cyperaceae) was carried out, including representatives of the three subgenera that occur in the country: Limnochloa, Scirpidium and Eleocharis. The analyses showed chromosomes without centromeres, but with terminal nucleolar constrictions (satellites) in some chromosomes. The chromosome numbers varied from 2n= 6 in E. subarticulata and E. maculosa to 2n= 60 in E. laeviglumis, but the chromosome basic number x= 5 was confirmed. Species of the subgenera Eleocharis and Scirpidium possess fewer and larger chromosomes, while those in the subgenus Limnochloa have small and more numerous chromosomes. These features indicate that the karyotypes of the subgenera Eleocharis and Scirpidium are more closely related, in agreement with morphological and phylogenetical data. The representatives of the section Eleocharis exhibited the largest differences in chromosome number and size, probably due to chromosome fission and fusion. Polyploidy was the most common event in this group. Nevertheless, most of the studied species exhibited regular meiosis with only bivalent formation, even the polyploids, such as in E. geniculata and E. sellowiana. The cytogenetic information obtained showed quite variable karyotypes with chromosomes gradually decreasing in size, and predominance of polyploidy. These results are useful in the differentiation of the subgenera. Introduction Eleocharis R.Br. (Cyperaceae) is a genus with a worldwide distribution, including more than 200 species with a remarkable richness in South America (González-Elizondo and Tena-Flores 2000). The relatively simple morphology associated with a great phenotypic variation make difficult the identification and delimitation of the species (Simpson 1988; GonzálezElizondo and Peterson 1997; Trevisan and Boldrini 2008). There are few morphological characters that have taxonomic value in Eleocharis and several of them may be over-weighted, for example the ornamentation of the achenes and the number of style branches, which shows a high degree of homoplasy (González-Elizondo and Peterson 1997). The supraspecific classifications that have been proposed for Eleocharis, for example, Svenson (1929, 1939), Kukkonen (1990) and González-Elizondo and Peterson (1997), are based on morphological data, and can be considered preliminary due to the scarce diagnostic features. When morphology is compared with the current phylogenetic hypothesis, it seems to be clear that many morphological characters are either pleisiomorphic or have multiple origins (Roalson and Hinchliff 2007). To understand the evolutionary process in this group of plants, reviews are necessary that combine different approaches, as morphological, anatomical, cytogenetical and molecular markers, as suggested by González-Elizondo and Peterson (1997) and Roalson and Friar (2000). Molecular and cytogenetical analyses were useful to understand the evolutionary profile of two Cyperaceae genera from Japan. Fimbritylis Vahl was considered monophyletic and composed by three karyotype groups (Yano and Hoshino 2006a) and Schoenoplectus (Rchb.) with two clades with predominance of polyploidy (Yano and Hoshino 2005). Eleocharis, aswell as the other representatives of Cyperaceae, possess holocentric chromosomes, inverted meiosis and absence of tetrads with pseudomonad formation (Wahl 1940; Davies 1956; Strandhede 1965; Faulkner 1972). This family exhibits a wide range of chromosome numbers (Roalson 2008), originated by fusion (symploidy), fission (agmatoploidy) and polyploidy CSIRO PUBLISHING www.publish. csiro.au/journals/ajb Australian Journal of Botany, 2010, 58, 49–60 CSIRO 2010 10.1071/BT09185 0067-1924/10/010049 Table 1. Karyotype features of Brazilian species of Eleocharis R.Br. Species are grouped according to the supraspecific classification of GonzálezElizondo and Peterson (1997) Vouchers were deposited at the ICN herbarium of the Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil Species 2n Total length (mm) L/S (mm) Coordinates, localities (voucher number) Subgenus Eleocharis Section Eleogenus (Nees) Benth. and Hook. f. (1883) E. maculosa (Vahl) Roem. and Schult. 10 8 7 6 10.86 18.75* 19.04* 19.04* 2.3–1.8 4.4–2.0 4.3–1.8 4.4–1.8 3