1. Alliaria petiolata (M. Bieb.) Cavara & Grande (garlic mustard)
A. officinalis Andrz.
Pl. 311 i, j;
Plants biennial, terrestrial, glabrous or with sparse, unbranched, nonglandular
hairs, with the odor of garlic when fresh plants are crushed or bruised. Stems 30–120
cm long, erect or ascending, unbranched or branched from the base. Leaves
alternate and basal, 3–12 cm long, the uppermost sessile, the lower
ones with progressively longer petioles, the bases not clasping the stem. Leaf
blades triangular to broadly ovate, less commonly kidney-shaped, the margins
shallowly to coarsely toothed and wavy. Inflorescences racemes, sometimes
few-branched panicles with racemose branches, without bracts. Sepals
(2–)3–4 mm long, ascending, oblong-elliptic, shed soon after
the flower opens. Petals 4–7(–9) mm long, unlobed, white.
Styles 1–2(–3) mm long. Fruits spreading, straight or nearly
so, (2–)3–7(–8) cm long, more than 10 times as long as
wide, linear, somewhat 4-angled in cross-section, not beaked, dehiscing
longitudinally, each valve with a midnerve and 2 lateral, longitudinal nerves.
Seeds in 1 row in each locule, 2.0–4.5 mm long, oblong or narrowly
elliptic, the margins not winged, the surface with a pattern of longitudinal
ribs, black. 2n=42. May–June.
Introduced, scattered in the state, mostly in urban areas and in the Big Rivers
Division (native of Europe and Asia, widely naturalized in the U.S. and southern Canada). Bottomland and mesic
upland forests in valleys and floodplains of creeks and rivers, often in soils
derived from calcareous substrates; also in disturbed, mostly shaded sites.
This species originally escaped during the 1800s in the northeastern states,
probably from gardens. In Europe, it has a long history of use as a potherb,
salad green, garlic substitute, and source of fatty oils (from the seeds), and
medicinally as a diuretic, diaphoretic, expectorant, and treatment for asthma
and dropsy (Al-Shehbaz, 1988b). It is extremely invasive in moist, shaded
habitats and has become a serious threat to natural plant communities in much
of the eastern half of North America (Nuzzo,
1991, 1993). Cattle that graze on it produce garlic-flavored milk, and deer
usually avoid browsing on it. Characteristics of the species that promote its
ability to spread and become naturalized include self-compatibility of the
flowers and seeds that may persist in the soil for several years. Once
established, it rapidly replaces the native ground flora.
garlic mustard apparently was absent until recently. The earliest reports for
the state were from eastern counties (Mohlenbrock, 1979; Wiese, 1979), followed
quickly by reports from the western and southwestern areas (Henderson, 1980;
Nightingale, 1980). The plant has become widely established in floodplains of
the Missouri River and other rivers and is
expected to continue its spread in the state.