North Dakota), after leaves in the overstory had fully expanded and when Dirca palustris were similar phenologically at all sites (Table 1).
From each population we collected fully expanded leaves from 19 mature Dirca palustris selected to represent the spatial distribution of plants within the population.
Floral and vegetative traits differed among the populations of Dirca palustris, with the populations in Florida and North Dakota the most phenotypically distinct (Table 2).
Regarding precipitation, it may be that the specific habitats in which Dirca palustris occurs are similar in soil moisture despite differences in precipitation on the regional level, so interpretation of this correlation is difficult.
The high level of genetic differentiation we found among populations of Dirca palustris is characteristic of species that are long-lived, insect-pollinated, self-compatible or have gravity-dispersed seeds (Nybom and Bartish, 2000).
Further evidence for genetic divergence among populations of Dirca palustris was found in the results of pair-wise neighbor-joining analysis.
Our genetic results also provide insight on the phylogeography and conservation value of the populations of Dirca palustris we studied.
Populations like the one in North Dakota, which may both lack genetic diversity and be most adapted to conditions at the leading edge of range shifts as a consequence of directional selection during migration to new climates (Lacy, 1987), could be important for northward expansion of Dirca palustris in response to regional climate change (Davis and Shaw, 2001).
Leatherwood in Kansas: A morphological assessment of an anomalous population of Dirca palustris (Thymelaeaceae) [Abstract].