Leavenworthia uniflora (Michx.) Britton

Michaux's Gladecress

© SRTurner

Family - Brassicaceae

Habit - Annual forb.

Stems - Absent.

Leaves - Basal only, forming rosettes, petiolate, 2-10 cm long, oblanceolate in outline, pinnately lobed or divided, with 4-18 lateral lobes and 1 larger terminal lobe, these toothed or lobed, glabrous.

	Basal leaves.
© SRTurner

	Leaflets.
© SRTurner

	Leaf abaxial.
© SRTurner

Inflorescences - Flowers borne singly on long leafless scapes.

Flowers - Sepals 3.5-5.0 mm long, ascending, oblong, often turning purple with age. Petals 4, 5-7 mm long, 2.5-3.5 mm wide, obovate, rounded at the tip, white. Styles 1.5-3.0 mm long.

	Flowers.
© SRTurner

	Sepals.
© SRTurner

	Corollas.
© SRTurner

	Corolla.
© SRTurner

Fruit - Siliques, flattened, somewhat fleshy, erect, 1.5-3.0 cm long, not constricted between the seeds, longitudinally dehiscent. Seeds in 1 row per locule, 3-4 mm in diameter, circular, flattened, winged, the surface with a netlike or honeycomblike pattern of ridges and pits, dark brown.

	Fruiting plant.
© SRTurner

	Fruit.
© SRTurner

Flowering - March - April.

Habitat - Limestone and dolomite glades.

Origin - Native to the U.S.

Lookalikes - Leavenworthia torulosa, which is very rare.

Other info. - This little plant may be Missouri's smallest mustard, typically standing only a few inches high. It occurs mostly in the southern half of the state, always on calcareous glades where the soil is thin and rocky. Its entire global range is limited to a few states in the east-central portion of the U.S. Missouri probably has the largest population of any state.

This plant typically occupies the same type of habitat as the cyanobacterium "rock snot" (Nostoc), and the two can sometimes be found growing together. Once discovered, the plant is easily identified by its solitary flowers on leafless stalks and its characteristically divided leaves. The flowers, though small, are large in relation to the size of the plant. There is another species which looks similar, Leavenworthia torulosa, but this is extremely rare in Missouri. It differs by having notched petal tips and fruits which are constricted between the seeds.

Leavenworthia uniflora is a winter annual. Seeds germinate in the fall, producing leafy rosettes which persist over the winter. Flowering stalks are produced early the following spring, and after producing fruits the plants disappear.

Photographs taken at Washington State Park, Washington County, MO, 4-14-2011 and 4-21-2014, Valley View Glade Natural Area, Jefferson County, MO, 4-11-2014, St. Joe State Park, St. Francois County, MO, 4-26-2014, 3-31-2015, 4-11-2018, and 3-26-2020, and Shaw Nature Reserve, Franklin County, MO, 3-29-2023 (SRTurner).