Biosystematics of Gunnera (Gunneraceae) in the Hawaiian Islands

The dicotyledonous genus Gunnera (Gunneraceae) comprises 30 to 50 species of small to megaphytic herbs distributed primarily in the Southern Hemisphere. Gunnera is unique among the angiosperms because of its unusual intracellular symbiosis with the cyanophyte Nostoc. The taxonomy and evolutionary history of the genus is poorly understood because of the paucity of biosystematic studies on species of Gunnera. In an effort to learn more about the biology and evolution of this group of phylogenetically problematic angiosperms I conducted a biosystematic study of Gunnera species endemic to the Hawaiian Islands. Using data from phytochemistry, morphology, isozyme variation, and restriction-fragment analysis of nuclear ribosomal DNA (rDNA), I attempted to resolve the taxonomy and evolutionary history of the genus in Hawaii. In addition, I attempted to determine which features present in Gunnera are of potential systematic value at both the specific and familial level. Among the disparate data types employed in the study, only data obtained from the field and herbarium portions of the study provided useful taxonomic information concerning Gunnera in Hawaii. These data suggest the presence of a single species, Gunnera petaloidea (encompassing two subspecies: G. petaloidea spp. petaloidea and G. petaloidea spp. kauaiensis), as opposed to the seven taxa previously recognized. A formal taxonomic treatment is provided for both subspecies. It is hypothesized that G. petaloidea is the result of evolution in situ within the Hawaiian Islands following a relatively recent dispersal event from the Americas. Although the phytochemical data obtained was not of systematic value at the species level, it provided new data useful for comparative phylogeny at the familial level. The incorporation of molecular techniques (enzyme electrophoresis and restriction-fragment analysis of nuclear rDNA) did not yield usable comparative data because of low enzyme activity and degraded DNA, respectively. Enzymatic inhibition due to high concentrations of tannins in Gunnera combined with rapid degradation of harvested foliar material are presumed to be the primary obstacles to molecular analysis. Additional studies on Gunnera are necessary in order to more fully understand its biology as well as resolve its evolutionary history.