Recent studies indicate that the family Iridaceae consists of 1800 extant species classified in 60 genera and 4 subfamilies. Among subfamily Iridoideae and tribe Sisyrinchieae is the genus Sisyrinchium, commonly known as the blue-eyed-grasses. Although the majority of the Iridaceae are concentrated in Africa, Sisyrinchium is found exclusively in the New World with 80-100 species. Morphological identifications have been difficult with this group and many geographic areas have not been intensively studied, particularly in South America. However, research in North America indicates that chromosome numbers range from 2N=10 up to 2N=96, with most species being tetraploid. Polyploidy has been recorded for several taxa. No phylogeny has ever been developed for this genus. Our study is two-fold: 1) to determine a phylogeny for the genus using the trnL-trnF intergenic region of the chloroplast DNA (cpDNA) and ISSR techniques, and 2) to look at the genetic variation and the correlation between guard cell area and chromosome number throughout the geographic range of S. atlanticum Bickn., a reported polyploid taxon. Using molecular data, a phylogeny was generated but not all taxa were resolved. Detectable variation exists across the range of S. atlanticum with correlation between guard cell area and chromosome number from 20 populations indicating at least 2 if not 3 ploidy levels.

Key words: evolution, Iridaceae, Sisyrinchium