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.