Hibiscus dasycalyx

Abstract: Hibiscus dasycalyx is a rare eastern Texas endemic that shares key morphologic traits with two widespread sympatric congeners, H. laevis and H. moscheutos. Working with an initial hypothesis that these taxa were possible ancestors of the endemic through diploid hybridization speciation, a ten-enzyme electrophoretic screening was conducted to determine whether H. dasycalyx exhibits a hybrid genetic profile. The three taxa share predominant alleles for all enzyme systems except ADH, GPI, and PGM, for which H. dasycalyx and H. laevis display generally identical banding patterns that differ from those of H. moscheutos. An analysis of diagnostic leaf shape and calyx pubescence features of eastern Texas H. laevis revealed substantial variation among populations, including forms intermediate between typical H. laevis and H. dasycalyx. In greenhouse hand-pollinations, H. dasycalyx plants serving as ovule parents were freely compatible with H. laevis. Due to the possession of identical isozymes, the occurrence of morphologically intermediate populations where the species cooccur and exhibit an apparent lack of reproductive isolation, the endemic H. dasycalyx may be best regarded as a subspecies or variety of H. laevis, the taxon it most resembles morphologically. Conservation efforts should consider the potential effects of contaminating gene flow with typical H. laevis. Many endemic plant taxa are closely allied to widely distributed species they resemble morphologically. Depending upon the degree, sharpness, and nature of the differences that separate an endemic from typical members of related species, the endemic may be regarded either as a variety, or a distinct species. Knowledge of the genetic affinities of endemic taxa can foster an understanding of evolutionary processes and also serve practical interests of plant conservation. Wisely, many of the state and federal programs that protect rare taxa include infraspecific categories within their purview. The delimitation of correct species boundaries, particularly when the endemic is found to comprise a subspecies or variety, may aid conservation biologists by alerting them of the potential for contamination of the endemic gene pool by hybridization with the species at large (Rieseberg, 1991). The biological species concept, that regards species as an interbreeding community of populations reproductively isolated from other such communities (Mayr, 1992), may be useful on a local scale in spite of its being neither universally applicable nor often practical to employ (Sokal and Crovello, 1970). The presence or absence of reproductive isolating mechanisms between sympatric taxa may assist in a determination of whether they represent the same or different species, particularly when used in conjunction with an analysis of patterns of morphological dissimilarity and the distribution of neutral genetic markers such as isozymes. Isozyme data may also be used to determine the most likely evolutionary mechanism by

Abstract: Winter-hardy hibiscuses are herbaceous perennials that regenerate from root buds each spring in USDA hardiness zones 5 through 9. Colloquially known as Rose Mallows, the most recent taxonomic revision (Blanchard, 1976) recognizes five species (Hibiscus coccineus Walter, Hibiscus dasycalyx Blake & Shiller, Hibiscus grandiflorus Michaux, Hibiscus laevis Allioni, and Hibiscus moscheutos L.) that comprise the North American taxon Hibiscus L. sect. Muenchhusia (Heister ex Fabricium) O. Blanchard (Malvaceae) (Small, 2004). A number of additional taxa associated with H. moscheutos have been variously recognized historically as varieties, subspecies, or distinct species. Primary among these are Hibiscus moscheutos subsp. palustris L., native to the northeastern United States, and Hibiscus moscheutos subsp. incanus Wendl., indigenous to the southeastern coastal plain (Blanchard, 1976). Native populations prefer wetland habitats such as flood plains but are tolerant to wide fluctuations in soil moisture. Rose mallows are long-day plants (Warner and Erwin, 2001) that flower from late spring through fall. Flowers last for a single day with color varying from scarlet rose in H. coccineus to white, lavender, and pink shades in the other four species. Studies of pollination in H. moscheutos indicate that the species is generally self-compatible but that the trait is variable with some lines rapidly develop inbreeding depression in progeny (Snow and Spira, 1993). The five species have a shared chromosome number of N =19, but artificial hybridization studies resulted in grouping the species into two groups based on seed set (Wise and Menzel, 1971). Hibiscus grandiorus and H. moscheutos (Group I) were entirely interfertile, and H. coccineus and H. laevis (Group II) were also interfertile, but crosses between groups produced few viable seed. Although Wise and Menzel (1971) did not include H. dasycalyx in their studies, subsequent work has shown that H. dasycalyx is closely related to H. laevis (Klips. 1995; Small, 2004) and clearly belongs in Group II. Although breeding of rose mallows has focused on developing new clones with improved horticultural traits (Malinowski et al., 2012) such as branching and flower color, there is a need for clones with improved disease resistance, particularly in the southeastern United States. Both ‘Lufkin Red’ and ‘Lufkin White’ have desirable horticultural traits in combination with demonstrated high levels of field resistance to the leaf spot complex (Pirone, 1970) that is problematic on winter-hardy hibiscus clones in areas with warm nights and high humidity.