1. Lamium amplexicaule L. (henbit)

Pl. 434 f, g; Map 1950

Stems 4–35 cm long, erect or ascending, often from a spreading base, unbranched or few-branched from at or near the base, glabrous or more commonly sparsely to moderately pubescent with short, downward-bent hairs. Leaves short- to long-petiolate (lower and often also median leaves), the shorter petioles often narrowly winged, the longer petioles usually unwinged, grading into sessile leaves (mostly those subtending flower clusters) that sometimes appear more or less clasping the stem. Leaf blades 5–15 mm long, unlobed or 3-lobed, the margins also with relatively coarse, blunt teeth or scallops, rounded to shallowly cordate at the base, rounded to bluntly pointed at the tip, the surfaces variously densely soft-hairy to nearly glabrous, those of the lower leaves ovate-triangular to broadly ovate or nearly circular, grading into those of the upper leaves, which are nearly semicircular to very broadly ovate or kidney-shaped, usually wider than long. Inflorescences with most of the nodes well-separated, the bractlets absent. Calyces 5–7 mm long, the tube and lobes densely bristly-hairy, the lobes shorter than to slightly longer than the tube. Corollas (except in cleistogamous flowers) 10–20 mm long, the outer surface sparsely to more commonly densely hairy, with a very dense patch of usually longer, darker hairs on the upper lip, the upper lip 3–5 mm long, rounded to shallowly notched at the tip, pinkish purple, rarely entirely white, the lower lip 1.5–3.0 mm long, usually lighter pink or white, with purple spots or mottling, rarely entirely white, the lateral lobes reduced to small convexities along the lip margin, the central lobe obcordate. 2n=18. February–May, rarely November–January.

Scattered to common nearly throughout the state, but apparently less common in most of the Glaciated Plains Division (native of Europe, Asia, Africa; introduced nearly throughout temperate North America). Edges of marshes, and openings of mesic upland forests; also crop fields, fallow fields, pastures, fencerows, lawns, sidewalks, railroads, roadsides, and open, disturbed areas.

Mennema (1989) treated L. amplexicaule as a complex of five varieties. In his classification, the introduced Midwestern material would correspond to var. amplexicaule. However, some of these varieties probably are better treated as separate species. More recently, based on a molecular-phylogenetic analysis of the genus, Bendiksby et al. (2011) determined that some of these non-Missouri taxa previously included within L. amplexicaule represent allopolyploid derivatives resulting from past hybridization between that species and other members of the genus. The situation requires further study. Rare plants with white corollas have been called f. albiflorum Dw. Moore (var. album Pickens and M.C.W. Pickens) and plants with all of the flowers cleistogamous have been called var. clandestinum Rchb.

Burrows and Tyrl (2001) reported that in Australian pastures livestock sometimes contract neurological problems (staggers) following ingestion of henbit, but that similar cases of toxicity are unknown from the native range of the species or from North America.