Chromosomal evidence for autotetraploidy in the Turnera ulmifolia complex (Turneraceae)
The hypothesis that tetraploids of two taxonomic varieties of the Turnera ulmifolia complex, vars. elegans and intermedia, have had autopolyploid origins, was tested. Chromosome counts within each variety show that two cytotypes occur with somatic numbers of 2n = 10 and 2n = 20. Tetrapoloids of both var. intermedia and var. elegans have pollen fertility approximately 13% less than that of diploids. Synthetic tetraploids produced by colchicine doubling exhibit pollen fertilities virtually identical to those of the natural tetraploids. While diploids exhibited only bivalent formation, tetraploids showed varying frequencies of univalents, bivalents, trivalents, and quadrivalents. The chromosome pairing model of R. C. Jackson and D. P. Hauber (1982. Am. J. Bot. 69: 644–646) and a minor modification of the goodness-of-fit test for that model, were used to test the hypothesis of an autopolyploid origin. For four of the six populations studied meiotically, the data fit the model. The data indicate that the tetraploid cytotypes of T. ulmifolia vars. elegans and intermedia have had autopolyploid origins. Key words: Turnera ulmifolia, autotetraploid, chromosome pairing model.