An essential challenge facing Conservation Biology today is the accurate identification of species that need protection. One example is the Neches River Rose Mallow (Hibiscus dasycalyx), found only in Texas, and listed by NatureServe Conservation Status as globally critically imperiled (G1). This means there are fewer than 3,000 individual plants known to exist in the wild.
This imperiled plant is a focus of ongoing conservation efforts at Collins Academy, where our work has helped to raise seedlings of this plant, which have been used by local schools and public parks and private landowners for conservation efforts. Collins Academy also maintains several Neches River Rose Mallow in the gardens at the Port Jefferson History and Nature Center.
One problem with species identification in plants is the potential for hybridization and crossbreeding. Hibiscus. dasycalyx co-ocurs with two other closely related plants in the same genera (H. moscheutos and H. laevis, known as congenerics). There are less than 10 naturally occurring populations of Hibiscus dasycalyx in the entire world. The geographically widespread and non-threatened congenerics H. moscheutos and H. laevis have overlapping ranges with H. dasycalyx, and sometimes even co-occur within locations.
How to tell these three species apart? It is not always possible with the naked eye, but some morphological characteristics stand out: H. moscheutos has large, heart-shaped leaves that are grayish-green above and hairy-white below; H. laevis and H. dasycalyx both have hairless and pointed leaves, making it difficult to tell them apart from each other with morphology alone.
Morphological variants in the field, as well as experimental crossings in the lab, suggest that these three species are capable of interbreeding with one another, but the extent of admixture, which occurs when two or more previously isolated populations begin interbreeding and results in the introduction of new genetic lineages into a population, is not currently known.
Previous studies by Joshua Banta, Ph.D. at the University of Texas at Tyler used genetic sequences and phylogenetic analyses to help resolve the taxonomic status of this federally threatened east Texas endemic wildflower. Genetic analysis was conducted on the gene for granule-bound starch synthase (GBSSI or waxy gene), which exists in a single copy in nearly all plants. The GBSSI gene is a low-copy nuclear gene used for phylogenetic analyse of plants because highly repetitive genes such as those commonly used are limited in number.
Dr. Banta showed that H. dasycalyx individuals share genetic similarities with one another, but there were misidentified specimens and advanced-generation hybrids (admixture) that were also identified in the dataset. Removing these, the sequence divergence between H. laevis and H. dasycalyx increased but remained low and the relationships between these species in the phylogenetic analysis remain poorly resolved. Based on this information, Dr. Banta hypothesized that H. dasycalyx may be a subspecies of H. laevis rather than a separate species. More genetic analyses based on additional genes will be necessary to confirm this result. This study highlights the need to understand species based on modern scientific methods, combined with traditional morphological observations.
Come visit Collins Academy and take a tour of the gardens at the Port Jefferson History and Nature Center to see the rare Neches River Mallow (Hibiscus dasycalyx) up close and in bloom.