False Motherwort (Chaiturus marrubiastrum)

Description: This herbaceous perennial plant is 1-4' tall and usually unbranched, except sometimes at the base. The central stem is light green, short-pubescent, and 4-angled with shallow vertical grooves. At intervals, there occurs pairs of opposite leaves that become slightly shorter and more narrow as they ascend the stem. Each pair of leaves rotates about 90° from the pair of leaves either immediately above or below. The leaf blades are 1-3" long, 1/3-1¼" (8-31 mm.) across, and flat; they are ovate to oblong-lanceolate in shape and their margins are dentate to sparsely crenate. The upper surface of each leaf blade is medium green and sparsely short-pubescent, while the lower surface is slightly more pale and pubescent (at least along the central veins). On each leaf blade, there are usually 2 lateral veins that run parallel to the central central and a few secondary veins that branch from the central vein along its length. The petioles of the leaves are ¼-¾" long. The lowest leaves, which are wider, are often withered by the time that flowering occurs.

The flowers occur in dense axillary clusters along the upper half of each stem; these floral clusters are whorled and sessile. Individual flowers are about ¼" (6 mm.) long and 1/8" (3 mm.) across, consisting of a 2-lipped tubular corolla with 4 lobes, a calyx with 5 teeth that have spine-like tips, 4 stamens, and a pistil with an ovary that is divided into 4 parts. The corolla is white to pink and softly short-hairy along the exterior of the upper lobe, which functions as a protective hood. There is also a rounded lower lobe and two smaller lateral lobes. A patch of red occurs within the throat of the corolla. The calyx is light green, sparsely canescent along its exterior, and 5-veined. The corolla of the flower is about the same length as the calyx (including the tips of its teeth) or a little longer. The blooming period occurs from Distribution Map

early summer to early fall for about 2-3 months. Usually, only a few flowers are in bloom at the same time across several floral clusters. Each flower is replaced by a cluster of 4 small nutlets during the fall. Individual nutlets are oblongoid and 3-sided. The root system is fibrous and rhizomatous. Clonal colonies of plants are often formed from the rhizomes.

Cultivation: The preference is full sun to light shade, moist to dry-mesic conditions, and loamy, rocky, or sandy soil that is calcareous. Depending on fertility of the soil, moisture levels, and time of year, individual plants can vary considerably in their height.

Range & Habitat: False Motherwort is uncommon to occasional in both central and NE Illinois, while in the rest of the state it is rare or absent. This plant is not native to Illinois; it was accidentally introduced into North America from Eurasia. Habitats include dolomite prairies, sandy savannas near Lake Michigan, riverbanks, roadsides, and pastures. This plant is usually found in disturbed areas, although it sometimes occurs in higher quality habitats.

Faunal Associations: Very little is known about floral-faunal relationships for this plant in North America, although they are probably similar to those for Motherwort (Leonurus cardiaca), which is closely related to False Motherwort and more common. The flowers are likely pollinated by various bees, including bumblebees, little carpenter bees (Ceratina spp.), and Halictid bees (Halictus spp., Lasioglossum spp.), which seek nectar or collect pollen from the flowers. Syrphid flies may also visit the flowers to feed on pollen, but they are less effective at cross-pollination. The Currant Aphid (Cryptomyzus ribis) uses Leonurus spp. (Motherworts) as summer hosts. Because of the bitter foliage, it is unlikely that mammalian herbivores browse on False Motherwort to any significant extent.

Photographic Location: A sandy oak savanna near Lake Michigan at the Indiana Dunes State Park in NW Indiana.

Comments: Across different populations, the leaf blades of False Motherwort can vary significantly in their width and in the abundance or size of the teeth along their margins. This plant is sometimes referred to as Leonurus marrubiastrum, but it differs from Leonurus spp. (Motherworts) by the lack of cleft lobes on its leaves. Like Motherwort (Leonurus cardiaca), False Motherwort can be distinguished from many other members of the Mint family by the spiny teeth of its calyces, the shape of its leaves, and other characteristics. Other common names of this plant are Lion's Tail and Horehound Motherwort.