Polyploidy: a factor in the evolution of Dicerandra Benth. (Labiatae)

Abstract

Chromosome counts are reported for the first time in Dicerandra Benth. (Labiatae), a genus endemic to the south-eastern United States. Representative taxa are tetraploid (« = 16) and hexaploid (n = 24). Diploids were not found. The systematic, phytogeographic and conservation implications of polyploidy in this genus are discussed. The monophyletic nature of the genus is upheld by the discovery that both sections have a presumed base number of x = 8. Hexaploidy has apparently evolved independently in all branches of sect. Dicerandra, but not in sect. Lecontea.

Molecular phylogeny, biogeography, and systematics of Dicerandra (Lamiaceae), a genus endemic to the southeastern United States

“…For this reason, long-distance seed dispersal in Dicerandra was proposed to be accomplished mainly by rainstorms that would carry the buoyant mucilaginous fruit along ancient waterways in the southeastern United States (Huck, 1987), but could also be facilitated by high winds associated with hurricanes. Huck and Chambers (1997) hypothesized that successive falling and rising of sea level during the Pleistocene were responsible for the appearance of appropriate habitats in isolated areas in Georgia and Florida. In agreement with these hypotheses, our investigation uncovered a distinct phytogeographic pattern showing that closely related taxa occur in adjacent areas.…”

“…1) (Huck and Chambers, 1997). Six of these nine species have widely disjunct, but extremely small, geographic ranges and are confined to sites within regions harboring high levels of endemism (Ward, 1979;Zona and Judd, 1986;Huck et al, 1989;Christman and Judd, 1990;Sorrie and Weakley, 2001).…”

“…immaculata, which are hexaploid (n ¼ 24), and D. immaculata var. savannarum, the ploidy of which is still unknown (Huck and Chambers, 1997;Huck, 2001). No diploids are known.…”

“…Currently, section Lecontea Huck comprises two annual species (D. odoratissima and D. radfordiana) and is distinguishable primarily by corolla design, stamen orientation, and the cinnamon-like odor of the leaves (Huck et al, 1989;Huck and Chambers, 1997). Section Dicerandra contains the remaining species and is characterized mainly by the presence of an infundibular corolla and a strong mint fragrance when the leaves are crushed (Huck, 1987;Huck and Chambers, 1997). Dicerandra christmanii, however, has a distinctive array of fragrance compounds with 1,8-cineole predominating; its crushed leaves smell like eucalyptus oil (Huck et al, 1989).…”

Parent Genotype and Environmental Factors Influence Introduction Success of the Critically Endangered Savannas Mint (Dicerandra immaculata var. savannarum)

“…The plant genus Dicerandra (Lamiaceae) contains four annual and five perennial species that are restricted to scrub and sandhill habitats primarily in Florida [13], [14] and is the highest ranked genus of rare southeastern endemic plants [12]. Six of the nine species have extremely small geographic ranges, there is probably little gene flow between populations, and their habitats are being converted for agricultural and urban development [10], [12], [15]–[17].…”