Ecophysiology and population genetics of Frangula caroliniana (Walt) Gray (Rhamnaceae)

Frangula caroliniana (Walt.) Gray (or Rhamnus caroliniana Walt.) (Carolina buckthorn) is a woody species distributed throughout the southeastern United States. Due to its ornamental characteristics and the various soil conditions in which it grows, there is interest in promoting the species as a nursery crop within and beyond its native range. Concerns about the invasive potential of F. caroliniana need to be alleviated before it is promoted in horticultural commerce. These concerns are based on the aggressive spread of related species introduced to North America, including Rhamnus cathartica L. (common buckthorn). Thus, I sought to assess the landscape fitness of F. caroliniana by comparing some of its ecophysiological traits to those of R. cathartica . In addition, I determined the genetic structure of F. caroliniana through analysis of populations indigenous to 16 states. Frangula caroliniana fixed carbon at rates that permitted its survival in soils that ranged from dry to wet, but plants with inundated roots did not survive. Cold stratification at 4°C for up to 112 days enhanced seed germination of F. caroliniana, but its seeds were more resistant to germination than were seeds of R. cathartica. Vernal bud break of F. caroliniana occurred 5.7 days later than that of R. cathartica, and depth of cold hardiness of F. caroliniana (-21°C) may permit use of provenance-based selections of the species in regions where winters are harsher than those of the native habitat. While fruit set per unit stem length and unit leaf area of F. caroliniana was only 41% of that of R. cathartica, seedlings of both species established similarly in field soils. Analysis of amplified polymorphism fragment length (AFLP) markers revealed two distinct groups of genotypes of F. caroliniana; the first group was comprised of plants from South Carolina, which had the highest source of genetic variation, and the second consisted of the other sampled F. caroliniana populations from 15 states. I conclude that the fitness for managed landscapes of F. caroliniana is promising, and that F. caroliniana lacks the capacity to be as invasive as R. cathartica