Observations of Tripsacum dactyloides and T. floridanum (Poaceae): measuring climate and soil gradient effects on Tripsacum in Texas, U.S.A.

Abstract

Reports of Tripsacum floridanum Porter ex Vasey in Texas have been countered with two arguments. First is that narrow-leafed Texas plants, when grown under favorable conditions, are more typical of wider-leafed T. dactyloides (L.) L. Second is that the offspring from crosses of T. dactyloides with T. floridanum are sterile or partially so. The support for these two claims is examined. The conclusion is narrow-leafed Texas plants typical of T. floridanum are in Texas, and crosses between the two produce fully fertile offspring. This raises the question of what factors are at play to segregate the wider-leafed from the narrower-leafed Texas populations. To investigate, two statistical models were constructed using separate data. First, a simultaneous system of seven equations was used to predict phenological and morphological plant characteristics given environmental factors. Second, a single logit equation predicted the probability of narrow-leafed diploid versus widerleafed diploid and tetraploid plants given environmental factors. Predictions allow for the measurement of plant characteristics from climate and soil gradients. Results suggest that narrow-leafed diploid plants occupy distinct habitats with the larger tetraploid plants coping by adapting mechanisms to overcome interspecies competition while the smaller diploid plants adapt with mechanisms to overcome stress. In conclusion, findings support consideration of T. floridanum as a variety of T. dactyloides and conservation implications are reviewed.