Leitneria floridana is a rare, woody, dioecious species often considered to constitute a monotypic family, the Leitneriaceae.  The species is known to occur in a disjunct distribution in the southeastern and south-central United States, but little is known about the comparative biology of the disjunct populations or the factors contributing to the rarity of L. floridana.  We studied populations in Missouri, Arkansas, Texas, and Florida to characterize and compare population density, habitat, ecophysiology, morphology, and growth.  Transects were established at each site and morphological measurements of plants included: plant height; trunk diameter at root collar; number of branches in the canopy of each plant (excluding the primary stem); number of leaves per branch; plant growth (length of the current season’s growth on the primary stem); and length, width, and area of the youngest fully expanded leaf.  Photosynthesis, soil moisture, and soil chemical components also were measured, along with recording the other dominant woody species in the study plots.  These measurements were used to estimate plant growth responses in relation to irradiance and soil moisture.

Results/Conclusions

Plants of L. floridana in Missouri were the most unique phenotypically. They were tallest, had the most elliptic leaves, and had a greater trunk diameter, a stouter trunk shape, and more branches per meter of plant height than did plants in Texas and Florida.  Plants in Texas showed the greatest annual increase in stem length, and plants in Arkansas seem particularly adapted to shade.  We found that L. floridana grows in chemically and physically diverse soils (pH 4.6 to 6.4) and under a broad range of insolation.  Data analyzed across provenances showed that photosynthetically active radiation was not correlated with the density of plants of L. floridana or with their growth.  Soil moisture content appears to be the most important environmental factor governing the occurrence of L. floridana, with soil moisture and distribution density positively correlated.  This evidence, and the occurrence of natural populations exclusively in wet habitats, suggest that alteration of hydrology by ditching and draining of wetlands for agriculture, forestry, and development is the greatest threat to L. floridana.  Restoration efforts should focus on wet sites where the likelihood of extended periods of drought is low.