tower mustard

Native

Dry. Prairies, fields. Full sun.

May to June

White

12″ to 60″

This is a 12″ to 60″ tall, erect, biennial or short-lived perennial forb that rises on one or more stems from a stout taproot.

In the first year the plant produces a rosette of basal leaves. These leaves are green or grayish green, up to 1½″ long, ¾″ wide, and inversely lance-shaped, with the attachment at the narrow end. The margins have outward-pointing teeth and shallow lobes. The upper surface is hairy, becoming less hairy with age.

One or more stems are produced in the second year. They are erect, usually unbranched, sometimes forked, leafy, and hairy near the base; hairless, light green and covered with a whitish, waxy coating (glaucous) above.

Stem leaves are alternate, overlapping near the base, less so above. They are up to 3″ long and 1″ wide, grayish-green, lance-shaped, hairless, and glaucous. A pair of lobes at the base of the leaf blade clasps the stem. Middle and upper stem leaves are untoothed. Lower stem leaves are toothed, slightly lobed, and commonly have Y-shaped hairs.

The inflorescence is an tight, short cluster at the end of the stem.

The flowers are ¼″ to ½″ wide. The 4 petals are white.

The fruit is an upward pointing, 2″ to 3½″ long, narrow, almost cylindrical pod that is roundish in cross-section. The fruits develop below the inflorescence.

Taxonomy
Tower mustard was placed with one other species in the genus Turritis when it was first described by Carl Linnaeus in 1753. In 1772, Giovanni Antonio Scopoli moved the second species to the genus Arabis based on seed arrangement, leaving Turritis with a single species. In 1783, Jean-Baptiste Lamarck transferred tower mustard to the genus Arabis with the new species name Arabis perfoliata. In 1800, Johann Jakob Bernhardi corrected the classification, renaming it Arabis glabra. In 2009, Koch et al. transferred it back to Turritis based on DNA analysis.

Plant

Leaves

Flowers

Infructescence