Observations on the Cytology, Morphology, and Ecology of Bradburia hirtella (Compositae-Astereae)

Bradburia hirtella is a small annual endemic to eastern Texas and Louisiana. The species includes two cytotypes n = 3 and n = 4, the latter known from only one plant. Under cultivation an n = 4 individual existed as a short-lived perennial blooming several times over the course of 2.5 years. The two cytotypes were crossed and the 2n = 7 progeny survived and bloomed. Meiosis was studied in 2n = 6, 7, and 8 individuals. Three bivalents were typically observed in late prophase and metaphase I in pollen parent cells of 2n = 6 plants. Four bivalents were typical in the 2n = 8 plant. In meiosis in the 2n = 7 plants, bivalents and multivalents were observed. The mitotic meta- phase karyotypes were also compared. Both the 2n = 6 and the 2n = 8 plants had one large acro- centric pair and a smaller acrocentric satellite chromosome with a short arm with subequal satellite and proximal portions. The 2n = 8 plant had two small metacentric pairs. The 2n = 6 plants had only one large submetacentric pair. The presumed closest relatives are in Chrysopsis. Efforts to cross Bradburia with several species of Chrysopsis were unsuccessful. Flavonoid patterns in the two genera were similar but did not confirm or refute a close relationship. On the basis of karyotypes the n = 4 race of Bradburia appears to be intermediate between the n = 4 perennial C. mariana and the more specialized n = 4 annual C. pilosa. While B. hirtella could be transferred to Chrysopsis, the distinctive staminate disc florets of the former are considered sufficient to separate the two at the generic level.