Sand Cress (Arabidopsis lyrata)

Description: This wildflower is a biennial or short-lived perennial that forms a low rosette of basal leaves, from which one or more flowering stems develop that are 4-14" long. The basal leaves are ¾-2" long and ¼-½" across; they are oblanceolate to oblong-oblanceolate and pinnatifid (rarely without lobes). The terminal lobes are larger in size than the lateral lobes. The upper and lower surfaces of the basal leaves are grayish green and either short-hairy or glabrous. The stems are erect, ascending, or sprawling; they are usually short-hairy below and glabrous above, but sometimes glabrous throughout. These stems are either branched above or unbranched. The alternate leaves along each stem are ½-1½" long and up to ¼" across; they are linear-elliptic, linear-oblanceolate, or linear-oblong in shape with smooth margins (rarely lobed or sparsely dentate). The alternate leaves are grayish green, sessile, glabrous along their upper surfaces, and either glabrous or short-hairy along their lower surfaces.

Each upper stem terminates in a raceme of flowers. The flowers bloom near the apex of each raceme, while seedpods develop below. Each flower spans ¼" across or a little more, consisting of 4 white petals, 4 green sepals, several stamens, and a pistil with a short style. The sepals are lanceolate with blunt tips and glabrous. The slender pedicels are ¼-½" long and glabrous. The blooming period occurs from late spring to late-summer, lasting about 1-2 months. The flowers are replaced by narrowly cylindrical seedpods (siliques) that are ¾-1¾" long, ascending, glabrous, and somewhat flattened. Each seedpod contains a single row of seeds. The seeds are about 1.0 mm. long, ovoid in shape, and somewhat flattened; they do not possess winged margins of any significance. The root system consists of a taproot. This wildflower reproduces by reseeding itself.

Cultivation: The preference is full or partial sun, mesic to dry conditions, and soil that is sandy, gravelly, or rocky. Competition from taller ground vegetation is not tolerated.

Range & Habitat: The native Sand Cress is occasional in northern Illinois, while in the rest of the state it is absent (see Distribution Map). In addition to its range in North America, this species is also found in Eurasia. Habitats consist of upland sand prairies, upland gravel prairies, sand dunes near Lake Michigan, sandy upland savannas, sandy upland woodlands, dry areas along sandy paths, and rocky cliffs along rivers. Occasional wildfires are probably beneficial in maintaining populations of this species.

Faunal Associations: The nectar and pollen of the flowers attract small bees, Syrphid flies, and small butterflies, including the endangered Lycaeides melissa samuelis (Karner Blue). Other insects feed destructively on the foliage, flowers, and other parts of Sand Cress and other plants in similar genera (Arabis spp., Boechera spp., etc.). These species include the flea beetles Phyllotreta conjuncta and Phyllotreta punctulata, caterpillars of Plutella xylostella (Diamondback Moth), and caterpillars of the following Pierid butterflies: Anthocharis midea (Falcate Orangetip), Euchloe olympia (Olympia Marble), Pieris napi (Mustard White), and Pontia protodice (Checkered White). For North America, little is known about the interrelationships of Sand Cress with vertebrate animals.

Photographic Location: A sandy savanna and open sand dune at the Indiana Dunes State Park in NW Indiana.

Comments: Sand Cress (Arabidopsis lyrata) is somewhat variable across its range and several subspecies have been proposed that are differentiated by the shape of the basal leaves and hairiness of the foliage. It is similar in appearance to Arabidopsis thaliana (Mouse-Ear Cress), Cardamine hirsuta (Hairy Bitter Cress), and Cardamine parviflora arenicola (Small-Flowered Bitter Cress). Sand Cress has slightly larger and showier flowers (6-8 mm. across) than the preceding species. Other characteristics that are useful for identification purposes include: 1) whether or not the basal leaves are lobed, 2) whether or not the cauline leaves along the stems are lobed, 3) whether the siliques are erect, ascending, widely spreading, or drooping, and 4) the length of the siliques. A scientific synonym of Sand Cress is Arabis lyrata, while another common name of this species is Lyre-leaved Rock Cress.