1. Glechoma hederacea L. (ground ivy, gill-over-the-ground)

G. hederacea var. micrantha (Boenn. ex Rchb.) Nyman

Pl. 434 a, b; Map 1947

Plants perennial, with fibrous roots, sometimes forming loose mats. Stems 10–200 cm long, prostrate (sometimes with short, ascending branches), rooting at the nodes, mostly sharply 4-angled, branched, glabrous or minutely roughened along the angles, also usually with a line of longer bristly hairs at the nodes. Leaves opposite, mostly long-petiolate. Leaf blades 1.0–2.5(–4.0) cm long, 1.0–2.5(–5.0) cm wide, broadly kidney-shaped to nearly circular, shallowly to deeply cordate or occasionally broadly rounded to truncate at the base, rounded or broadly angled to a bluntly pointed tip, unlobed, the margins coarsely scalloped or bluntly toothed, sometimes also minutely hairy, the surfaces glabrous or less commonly sparsely short-hairy, the undersurface also with usually inconspicuous sessile glands. Inflorescences axillary, clusters of 2–6 flowers per node, these with stalks 1–3 mm long. Bractlets scalelike or hairlike, 1.0–1.5 mm long, linear to narrowly triangular, mostly shorter than the associated flower stalk. Calyces 4–7 mm long, slightly zygomorphic (the upper lobes slightly longer than the lower ones), lacking a lateral projection, symmetric at the base, more or less cylindric to narrowly bell-shaped, the tube 15-nerved, glabrous in the mouth, the lobes shorter than the tube and more or less equally loosely ascending, oblong-elliptic, tapered to short-spinescent tips, sparsely to moderately pubescent with minute crinkly hairs on the outer surface, not becoming enlarged at fruiting. Corollas 10–18(–22) mm long, zygomorphic, purplish blue to purple (rarely white), the lower lip usually with white and darker mottling or spots, the outer surface moderately to densely pubescent with short, straight, more or less spreading hairs, the tube funnelform, 2-lipped, the lips shorter than the tube, the upper lip narrowly obcordate, notched at the broadly rounded tip, straight and not noticeably hooded, the lower lip with 3 spreading lobes, the larger central lobe shallowly notched at the tip, longer and much broader than the 2 lateral lobes, with a beard of fine spreading hairs internally near its base. Stamens 4, not or only slightly exserted (ascending under the upper lip), the filaments of 2 lengths, the anthers small, the connective short, the pollen sacs 2, spreading, white or purplish- to bluish-tinged. Ovary deeply lobed, the style appearing nearly basal from a deep apical notch. Style usually slightly exserted, with 2 slender branches at the tip. Fruits dry schizocarps, separating into 2–4 nutlets (sometimes these failing to mature), these 1.5–2.0 mm long, narrowly ovoid to oblong-ovoid or oblong-ellipsoid, the surface light brown to yellowish brown, glabrous, smooth or finely pebbled. 2n=18, 36 (2n=24, 45, 54 elsewhere). March–July.

Introduced, scattered nearly throughout the state, but mostly absent form the western portion of the Glaciated Plains Division (native of Europe, Asia; introduced nearly throughout the U.S., Canada, and in portions of the southern hemisphere). Bottomland forests, mesic upland forests, banks of streams, rivers, and spring branches, and bases of bluffs; also lawns, gardens, railroads, roadsides, and shaded, disturbed areas.

Böllmann and Scholler (2004) documented the distribution and historical spread of ground ivy in North America from its initial report from the eastern United States in 1814 to its present nearly cosompolitan distribution in temperate North America. According to them, the earliest specimen from Missouri was collected in 1868 along the Meramec River (St. Louis County). Böllmann and Scholler also noted that although the plant reproduces principally vegetatively by stem fragments, it can spread by nutlets that produce an adhesive mucilage when moistened. Today, the plant is considered a nuisance in lawns and gardens (and in disturbed floodplain habitats), capable of growing up to 2 m in a single year and continuing to elongate under the leaf litter during the winter. The foliage does produces a mildly unpleasant odor when crushed. Steyermark (1963) and Burrows and Tyrl (2001) noted livestock poisoning after animals ingested large quantities of the species fresh or in hay (but the causal toxins remain unknown).

The infraspecific taxonomy of G. hederacea is not well understood and several varieties and subspecies have been described. Polyploidy also plays a role in the morphological variability of the species (Iwatsubo et al., 2004). Currently, most Asian and European botanists do not divide G. hederacea into infraspecific taxa in its native range, but further study to correlate the cytological and morphological variation may result in the resurrection of one or more of the subspecies. Some North American botanists have recognized plants with smaller flowers as var. micrantha (Steyermark, 1963), but such individuals intergrade completely with larger-flowered plants. Both extremes have been recorded from Missouri.