Cytotaxonomic Studies of Louisiana Irises

Karyotype analyses of the species of Louisisana iris, Iris fulva (2n = 42), I. giganticaerulea (2n = 44), I. brevicaulis (2n = 42) and Abbeville Red (2n = 42) were made to determine whether natural hybridization, known to occur readily among these species, has altered the number or form of their chromosomes through introgression. 2. I. fulva is characterized by one long pair and one short pair of marker chromosomes with median constrictions. 3. I. giganticaerulea has no long chromosomes with median constriction but a short pair with median constriction is typical of this species. 4. I. brevicaulis of Southern Louisiana is a cytologically distinctive species having a karyotype consisting of a pair of unusually long submedian chromosomes with a secondary constriction in the long arm and one pair of short chromosomes with a secondary constriction next to the very minute short arm. 5. The Abbeville Reds are a distinctive population combining certain phenotypic characteristics of I. fulva and I. giganticaerulea. The karyotype is very similar to that of I. fulva except that it has an extra pair of short chromosomes in which the constriction is submedian rather than median. The remaining chromosomes are morphologically indistinguishable from those of I. fulva and I. giganticaerulea. 6. The natural affinities of the Abbeville Reds are discussed from the standpoint of distribution, habitat requirements, phenotypic characters, and karyotype.