Weed Identification

Here is the info I recieved from the UNH Cooperative Extension Office. It was indeed a member of the Mustard Family.

ED

Tower Mustard
Arabis glabra
Mustard family (Brassicaceae)

Description: This native biennial plant consists of a low-growing rosette of basal leaves up to 7″ across during the 1st year. These basal leaves are up to 3½” long and ¾” across; they are green to greyish green, oblanceolate, dentate, and often slightly pinnatifid with shallow lobes. Their upper surface is often hairy, although they tend to become less hairy with age. During the 2nd year, Tower Mustard bolts during the spring and produces one or more flowering stalks up to 3½’ tall. These stalks are light green to dull white, unbranched, hairless, and glaucous. Sometimes there may be a few hairs near the base of the stalks. The alternate cauline leaves are up to 3″ long and 1″ across. They are greyish green, lanceolate, smooth along the margins, hairless, and glaucous. Some of the lower cauline leaves may be dentate and slightly pinnatifid. The base of each cauline leaf clasps the stalk with a pair of basal lobes, which may be rounded or pointed. During cool spring weather, the cauline leaves may turn purple when they are exposed to full sun. Each stalk terminates in an elongated raceme of flowers and upright siliques (slender cylindrical seedpods). This raceme can become as long as the rest of the plant (up to 1¾’ in length) and it has a tower-like appearance. Each flower at the apex of the raceme is up to 1/6″ across, consisting of 4 white or cream petals, 4 light green or yellow sepals, a stout style, and several stamens. The pedicels of the flowers and siliques are about ¼–½” in length.

The blooming period occurs during late spring to mid-summer and lasts about 1½ months. Each flower is replaced by a slender cylindrical silique up to 2½” long. The siliques are held upright close to stalk of the raceme. Each silique contains 1 or 2 rows of slightly flattened ovoid seeds. These small seeds have narrowly winged margins and they are dispersed to some extent by the wind. The root system consists of a stout taproot. This plant spreads by reseeding itself.

Cultivation: The preference is full sun to light shade, mesic to dry conditions, and loam, clay-loam, or rocky soil. This plant also tolerates soil containing sand or hardpan clay. It is fairly easy to grow from seed.

Faunal Associations: Mostly small bees and flower flies visit the flowers for nectar or pollen. Occasionally various species of White butterflies (Pieridae) visit the flowers for nectar. The caterpillars of two Pierid butterflies, Anthocharis midea (Falcate Orangetip) and Euchloe olympia (Olympia Marble), prefer Arabis spp. (Rock Cresses) as a food source, particularly those Rock Cresses that are typically found in sunny habitats. The caterpillars of another Pierid butterfly, Pieris napi (Mustard White), reportedly feed on Rock Cresses, although this butterfly species hasn’t been observed in Illinois since the 19th century. Little information appears to be available about the desirability of Tower Mustard as a food source for mammalian herbivores; however, the foliage is not particularly bitter nor peppery.