Variation in plant- and leaf-level traits of Dicerandra (Lamiaceae) congeners native to sandhill communities and Florida scrub

Background/Question/Methods Endemic to the southeastern United States, the genus Dicerandra (Lamiaceae) consists of nine species displaying different growth habits in specific ecosystems.  Perennials are limited to small, geographically isolated scrub habitats along relict beach ridges and dunes within Florida’s peninsula.  Annuals range throughout recently disturbed sandhill habitats of Georgia and northern Florida.  Observations of Dicerandra within their native habitats find that species exhibit differences in plant- and leaf-level traits although all members of this genus are closely related.  It was not known if these divergences in traits are due to differences in genotype among the species or are phenotypic responses to each environment’s resource availability.  In this study, two sandhill and four scrub species were grown within a common garden under non-limiting light, nutrient, and water availability to determine genotypic differences among these species. 

Results/Conclusions

The growth habits of these species in their native habitat were exhibited in the common garden.  The perennial species which are native to gaps within scrub exhibited biomass allocation patterns, shoot architecture, leaf morphology, and leaf anatomy typical of plants acclimated and adapted to open, high-light environments.  Corresponding traits of the annual species native to the understory of sandhill habitats are similar to those found in plants acclimated and adapted to understory, shaded environments.  The ratio of leaf to stem tissue allocation was greater in perennial species.  Significantly greater plant height, internode length, and leaf size were found in the annual species.  A comparison of Dicerandra light-response curves did not find clear contrasts in the light-response curve components of annual and perennial species.  However, leaves of annual species exhibited bilateral leaf structure while leaves of perennial species were significantly thicker and displayed different degrees of isobilateral leaf structure.  The leaf tissue of perennial Dicerandra maintained significantly greater relative water content.  The comparison of traits exhibited by these congeners provides insight into characteristics important for plant fitness in Florida’s unique scrub communities.