Whitlow grass was the European name given to several inconspicuous wildflowers such as Saxifraga tridactylites, Draba verna and Paronychia which were thought to be a cure for the Whitlow. This is an infection of the end of the fingers and toes around the nail, as well as the hooves of animals, which caused painful inflammation. The genus Draba is from the Greek "drabe", meaning sharp or acrid, and refers to the burning taste of the leaves of these medicinal plants. Draba arabisans may be told from its closest New York relative, Draba glabella, by its twisted fruit and longer styles.
There are only 12 verified locations, with many historical locations remaining to be checked. This species is relatively inconspicuous and may occupy inaccessible habitats, and therefore may be overlooked.
Most currently known populations are small and persistent, but accurate and recent counts are lacking.
Many historical locations have not been observed for more than 25 years.
Most sites for this species are cliffs, and therefore relatively free from the threat of human disturbance; deer herbivory, fire, and succession may threaten some locations.
A buffer should be maintained around populations of this plant.
Research could help determine the reasons for the rarity of this species in New York and adjacent states.
Draba arabisans grows on dry cliffs, rocky ledges, talus slopes and open woodlands, often at calcareous sites. In New York Draba arabisans has been found on bedrock of limestone, shale and siltstone, and anorthosite. (New York Natural Heritage Program 2007). Rocks and cliffs (Gleason and Cronquist 1991).
There are scattered populations across the state, excluding Long Island and the lower Hudson Valley.
Draba arabisans occurs in the northeastern U.S. and eastern Canada, from Minnesota and Ontario in the west, across the Upper Great Lakes states, Ontario, and New York to northern New England (but excluding New Hampshire) Quebec, and Labrador. New York is on the southern boundary of its range.
Draba arabisans is a small (4 to 16 inches tall) herbaceous perennial, growing from a hardened base just underground (a caudex) to a basal rosette of hairy, 2.5 inch-long leaves, often dentate. From the rosette grows a single stem with a few dentate leaves and a loose terminal raceme up to 4 inches long, bearing 4-petaled flowers, the petals are yellow in bud but white upon opening. These mature into a flattened, lance-shaped fruit called a silique. The fruit are flattened, glabrous, and about 1/4 to 1/2 inch long.
Draba arabisans is a sturdy perennial growing from a thick caudex, 1-4dm tall, with many basal but few cauline leaves, the basal leaves narrowly oblanceolate to spatulate, up to 6cm long, often sharply toothed, and stellate -hairy. The stellate hairs are sessile and have 8 or fewer rays. The infloresence is a loose raceme up to 10 cm long, the pedicels without leaves or bracts, and glabrous or nearly so. The petals appear yellow in bud but are white after opening, and 4-6mm long. The persistent style is .3 to .8 mm long. The fruits are glabrous siliques, 7 -12 mm long and .2x to .25 x as wide as long, lanceolate to narrowly oblong, twisting during maturation, but shorter, ovate, and straight in depauperate specimens.
Draba arabisans is most easily identified when it is flowering, this occurs from late May through early July, depending on site (and microsite) conditions. Fruiting individuals can also be keyed successfully.
New York has 3 other species of Draba. Draba verna, an exotic species, is an annual, more slender than D. arabisans, with deeply split petals. D. reptans is also a slender annual, with entire basal leaves 3 cm long or less, shorter than the sharply toothed basal leaves of D. arabisans, which may reach 6cm. Both of these species are typically found in sandy or disturbed habitats. The only other perennial Draba in New York, which like D. arabisans is found on cliffs and rocks, is Draba glabella. Very similar to D. arabisans, D. glabella has untwisted fruits, typically .25x to .4x as wide as long, with the style obsolete or only 0.1 to 0.3mm, and its leaves have stellate hairs that are stalked and with 9 or more rays. So far it is known in New York only from Washington and Clinton counties in the northeast.
Draba arabisans flowers from late May until late June, with fruits visible usually through the beginning of October. Individual plants may be found with flowers at the top of the infloresence and developing fruit below, which may be helpful in identification.
The time of year you would expect to find Rock Whitlow Grass flowering and fruiting in New York.
Rock Whitlow Grass
Draba arabisans Michx.
Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.
Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.
New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.
New York Natural Heritage Program. 2021. New York Natural Heritage Program Databases. Albany, NY.
Voss, E.G. 1985. Michigan Flora. Part II. Dicots (Saururaceae - Cornaceae). Cranbrook Institute of Science and University of Michigan Herbarium. Ann Arbor, Michigan. 724 pp.
Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research http://www.fccdr.usf.edu/. University of South Florida http://www.usf.edu/]. New York Flora Association http://newyork.plantatlas.usf.edu/, Albany, New York
Information for this guide was last updated on: January 13, 2009
Please cite this page as:
New York Natural Heritage Program. 2021. Online Conservation Guide for Draba arabisans. Available from: https://guides.nynhp.org/rock-whitlow-grass/. Accessed July 26, 2021.