Cardamine impatiens L. (Brassicaceae) in New Jersey

Journal of the Torrey Botanical Society, Jul-Sep 2004 by Glenn, Steven D, Barringer, Kerry

Studies of the dispersal of Asian plants showed a mean seed flight distance of .8 to 1.2 meters, with the greatest distance being 2.2 meters (Kimata 1983, Nakanishi 1988); although an earlier European investigation stated a maximum ejection range of 2.5 meters (Overbeck 1925). Williams (2000) showed an average spread of 17 meters per year over one decade.

Cardamine impatiens may have a predominantly bi-modal dispersal system. Kimata (1983) found germinations rates of over 56 percent in distilled water 1 cm deep. This ability of seeds to germinate in water along with a distribution of plants predominantly on floodplains and along streams suggests that flowing water is the primary means of long-range seed dispersal in C. impatiens. Mechanical dispersal by tossing the seeds appears to be the chief means of shortdistance dispersal. Hydrochory permits longrange dispersal by spreading seeds within a riparian system; then active autochory allows it to expand locally.

When moist, the seeds stick readily to shoes, socks and pants even though the seed coat is not glutinous. The small size of the seeds apparently allows them to stick by surface tension. This could allow for adhesion to hooves and fur as well as boots and motorized vehicle tires and suggests a potential for plants to be dispersed outside of floodplains. Epizoochory probably plays a minor component in the seed dispersal system, accounting for the occasional appearance of isolated populations in mesic lawns, footpaths, roadsides, and forests and the one occurrence in Monmouth County (Figure 1) which was along a heavily used footpath.

Williams (2000) found large annual variations in the total number of individuals and in individuals per colony and suggested that C. impatiens is intolerant of competition. Margules et al. (1994) suggested that C. impatiens has high rates of local colonization and extinction. Populations may benefit from recent disturbance, common in floodplain habitats.

Cardamine impatiens exhibits potential to be an invasive weed and should be carefully monitored, especially in susceptible hydric to mesic habitats. Some of its reproductive characteristics suggest invasiveness: a self-compatible pollination system (Baker 1955, Baker 1974, Baker 1986, Lodge 1993), and prolific production of small seeds (Baker 1974, Harper et al. 1970, Rejmanek and Richardson 1996). Other factors to be considered are the lack of any known natural enemies (Crawley 1987) and its large native distribution (Lodge 1993). Finally, an effective dispersal system with adaptations for short- and long-range dispersal and the ability to create numerous regional nascent foci (Baker 1974, Baker 1986, Bazzaz 1986, Moody and Mack 1988) may allow the species to spread rapidly in riparian corridors (Pysek and Prach 1993).

Literature Cited

BAKER, H. G. 1955. Self-compatibility and establishment after "long-distance" dispersal. Evolution 9: 347-349.

BAKER, H. G. 1974. The evolution of weeds. Ann. Rev. Ecol. Syst. 5: 1-24.

BAKER, H. G. 1986. Patterns of plant invasion in North America, p. 44-57. In H. A. Mooney, and J. A. Drake [eds.], Ecology of biological invasions of North America and Hawaii. Springer Verlag, New York, NY.