Basis for Listing

Jeffersonia diphylla reaches the northwestern edge of its geographic range in the forests of southern Minnesota. The forests were vast when settlers first arrived, but have since been largely supplanted by farm fields. All that is left today are small, isolated remnants in deep stream valleys where agriculture is impractical. Only a small number of these remnants are known to support viable populations of J. diphylla.

The first wave of forest clearing was for agricultural expansion, and occurred in the last half of the 19th century and the first half of the 20th century. We are now in a second phase of forest clearing that is accompanying rural residential and commercial expansion and the concomitant construction of roads, power lines, and pipelines. Another rapidly emerging threat is the invasion of non-native species into the few remaining forest habitats. Jeffersonia diphylla was listed as a special concern species in Minnesota in 1996.

  Description

Jeffersonia diphylla is a spring flowering perennial forb that may reach about knee high. There is no above-ground stem, instead the leaves and the flower stalks grow directly from an underground rhizome. The flower stalk is 10-20 cm (3.9-7.9 in.) high and has a single white flower. The flower is relatively large (up to 4 cm (1.6 in.)) and has 8 petals and 8 stamens. The leaves are somewhat shorter than the flower stalk in the spring, but each leaf petiole continues to lengthen into summer and may eventually reach 30-40 cm (11.8-15.7 in.). Each leaf blade is 8-15 cm (3.1-5.9 in.) across and is divided into 2 equal-sized segments. It is these paired leaf-segments that give the plant its name "twin-leaf", and provide a fool-proof means of identification. The flower looks something like the flower of Sanguinaria canadensis (bloodroot), a common associate that flowers a week or two before J. diphylla, but the leaf of S. canadensis is not divided.

  Habitat

Jeffersonia diphylla occurs in mesic hardwood forests, specifically southern mesic maple-basswood forests (Minnesota Department of Natural Resources 2005). These forests are characterized by a continuous and dense canopy of deciduous trees, primarily Acer saccharum (sugar maple), Tilia americana (basswood), and Quercus rubra (northern red oak). These are quite stable, late successional communities with historic catastrophic windstorm intervals of over 650 years. Catastrophic wildfires were even more uncommon with a historic return interval of over 1,000 years in the bluff country where J. diphylla is found. The variety and abundance of forbs within these forest communities is severely limited by the deep shade. The rooting zone of the soil consists of moist loam with a substantial organic component. This type of forest has developed at several places in southern Minnesota, but only those that are found in the stream-dissected Blufflands of the southeastern counties harbor J. diphylla. Within these forests, J. diphylla tends to occur on north-facing slopes where conditions are cooler and moister.

  Biology / Life History

Jeffersonia diphylla is a perennial forb that flowers in early spring. It is not considered a spring ephemeral because the leaves remain intact and photosynthetically active all summer. They usually remain green until the first killing frost in October. Individual flowers remain open for 2-6 days and the entire flowering period lasts about 10-14 days (Smith et al. 1986). The flowers produce no nectar, but they do produce copious pollen, which attracts pollinators, primarily bees. If cross-pollination is not successful, autogamy (self-pollination) may occur (Smith et al. 1986).

The seeds are produced in urn-shaped shaped capsules 2-5 cm (0.8-2.0 in.) long. The top of the capsule functions as a lid, which pops open at maturity in mid-June. When the lid is open, the distal end of the peduncle bends, forcing the capsule to tip downward and spill the seeds onto the ground. The seeds have conspicuous elaiosomes (fleshy appendages that are rich in fatty acids and diglycerides), which are attractive to several species of ant. The ants gather the seeds and carry them to their nests, where the elaiosomes are removed and the seeds are discarded. The ants do not harm seeds, and in fact there is some evidence their behavior protects the seeds from predators (Heithaus 1981). Predation of seeds by rodents can be intense both before and after seeds are released from the capsule (Heithaus 1981). Deer can sometimes be a serious predator of the leaves, and if a plant is completely defoliated, it will survive but will likely not flower the following year (Rockwood and Lobstein 1994).

Freshly mature seeds remain dormant until autumn when embryo growth begins. The seeds resume dormancy over winter and germinate the following spring (Baskin and Baskin 1989). First-year plants will have only one small leaf with a petiole 3-5 cm (1.2-2.0 in.) long. In following years, the plant will produce progressively more leaves and the leaves will be larger until the plant reaches reproductive maturity in 3-5 years. There is no significant vegetative reproduction in J. diphylla. The rhizome is short and does not produce off-shoots.

Searching for J. diphylla does not have to be confined to the flowering or fruiting season. The leaves are large, relatively conspicuous and have a distinctive shape, and they can be seen from May through September.

  Conservation / Management

In Minnesota, J. diphylla typically occurs in stable, late successional forest communities that are able to perpetuate themselves without major disturbance or intervention. From a management perspective this means the forest can and, in most cases, should be left alone. Forest management practices that open gaps in the canopy or disturb the soil, and livestock grazing should be avoided. Hunting, maple syrup harvesting, nature study, and other low-impact uses will probably cause no harm as long as motorized vehicles are not used.

One notable exception to this "hands-off" recommendation pertains to ecologically invasive species, particularly such aggressive invaders as Rhamnus cathartica (common buckthorn) and Alliaria petiolata (garlic mustard). The threat caused by non-native species requires constant vigilance. Most infestations will be manageable if they are caught early and swift action is taken. Non-native earthworms are another serious threat to forests in Minnesota. Many people are surprised to learn that earthworms are not native to Minnesota. They arrived with people, either unintentionally with nursery stock or intentionally as fish bait or a soil amendment. They have gotten into native forests and caused considerable damage by consuming the duff layer of the soil. The duff layer is critical to the reproduction of many forest plants. The specific effect of earthworms on populations of J. diphylla is not known.

  Conservation Efforts in Minnesota

Jeffersonia diphylla is known to occur in a number of protected habitats, including two State Parks.

  References and Additional Information

Baskin, J. M., and C. C. Baskin. 1989. Seed germination ecophysiology of Jeffersonia diphylla, a perennial herb of mesic deciduous forests. American Journal of Botany 76(7):1073-1080.

Heithaus, E. R. 1981. Seed predation by rodents on three ant-dispersed plants. Ecology 62(1):136-145.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 394 pp.

Rockwood, L. L., and M. B. Lobstein. 1994. The effects of experimental defoliation on reproduction in four species of herbaceous perennials from northern Virginia. Castanea 59(1):41-50.

Smith, B. H., M. L. Ronsheim, and K. R. Swartz. 1986. Reproductive ecology of Jeffersonia diphylla (Berberidaceae). American Journal of Botany 73(10):1416-1426.