Leonurus japonicus Houtt.



CC = *
CW = 5
MOC = 3

© SRTurner

Family - Lamiaceae

Habit - Taprooted, annual or biennial forb.

Stem - Erect, to 2.2 m, 4-angled, finely and retrorsely pubescent.

Leonurus_japonicus_stem.jpg Stem and node.

© SRTurner

Leaves - Alternate, petiolate. Blades 2-15 cm long, those of the lower leaves ovate to nearly circular in outline and deeply 3-lobed, the lobes coarsely toothed and/or divided into slender lobes. Median and upper leaves linear in outline and lacking lobes and teeth to elliptic or ovate in outline and deeply divided from at or near the base into 3 slender lobes, the margins then entire or with a few coarse, sharp teeth, variously angled or short-tapered (lower leaves) or narrowly tapered (upper leaves) at the base, angled or tapered to a sharply pointed tip(s), the upper surface sparsely to moderately pubescent with short, fine, appressed hairs, the undersurface densely pubescent with fine, loosely appressed hairs.

Leonurus_japonicus_leaf1.jpg Lower stem leaf.

© SRTurner

Leonurus_japonicus_leaf1a.jpg Leaf adaxial surface.

© SRTurner

Leonurus_japonicus_leaf2.jpg Leaf abaxial.

© SRTurner

Leonurus_japonicus_leaf2a.jpg Leaf abaxial surface.

© SRTurner

Inflorescence - Dense axillary clusters, the flowers sessile.

Leonurus_japonicus_inflorescence.jpg Inflorescence.

© SRTurner

Leonurus_japonicus_inflorescence2.jpg Inflorescence node.

© SRTurner

Flowers - Calyces 5-8 mm long, finely 10-nerved, the nerves not thickened or riblike, the teeth shorter than the tube, densely and minutely hairy, also with numerous sessile glands. Corollas 10-14 mm long, distinctly longer than the calyces, pale pink to lavender, the lower lip usually with reddish purple spots or mottling, densely pubescent with short, fine, somewhat matted hairs externally except for the mostly glabrous lower lip. Stamens with the anther sacs parallel.

Leonurus_japonicus_flowers.jpg Flowers.

© SRTurner

Leonurus_japonicus_flowers2.jpg Flowers.

© SRTurner

Leonurus_japonicus_calyces.jpg Calyces and flowers.

© SRTurner

Fruits - Nutlets 1.5-1.8 mm long, truncate at tip.

Leonurus_japonicus_fruits.jpg Infructescences.

© SRTurner

Flowering - July - August.

Habitat - Barnyards, roadsides, disturbed areas.

Origin - Native to Eurasia.

Lookalikes - Broadly, other species of Leonurus.

Other info. - This is a rare plant in Missouri, having been found in only two counties so far. The plant was first collected in Missouri in 1990 by Father James Sullivan, who sampled a population in Weldon Spring which had been known locally for a decade or more. The population was still present as of 2020. The species is likewise rare in the U.S. beyond Missouri, reported from a few widely scattered areas mostly in the central U.S. Within the U.S. it appears to be common only in a small portion of Louisiana. The plant is easily recognized by its leaves. Near the base of the plant these are deeply lobed, with long, narrow, straplike segments. Toward the top of the plant the number of segments diminishes, with the uppermost being simple. The inflorescences are axillary clusters and the flowers 2-lipped, as is typical of mint family plants.

Photographs taken in Weldon Spring Conservation Area, 8-30-2009, 10-21-2009, 8-15-2011, 7-22-2018, and 8-20-2020 (SRTurner).