Stems simple or branched distally, (1.5-)3-9(-13) dm; glabrous or pilose basally, trichomes to 1.5 mm. Basal leaves: petiole 3-16(-22) cm; blade reniform or cordate, (6-)15-88(-118) mm wide (shorter in length), surfaces glabrous or pilose. Cauline leaves: petiole shorter than basal; blade ovate, cordate, or deltate, to 15 × 15 cm, base cordate or truncate, margins acutely to obtusely toothed, apex acute. Racemes several-flowered. Fruiting pedicels terete, (2-)3-10(-15) mm. Flowers: sepals (2-)2.5-3.5(-4.5) × 0.7-1.5 mm; petals (2.5-)4-8 (-9) × (1.5-)2-3(-3.5) mm, base attenuate to clawlike; filaments 2-3.5(-4.5) mm; anthers oblong, 0.7-1 mm. Fruits divaricate-ascending, subtorulose, quadrangular or subterete, (2-)3-7(-8) cm × 1.2-2.5 mm; style (0.2-) 1-2(-3) mm. Seeds dark brown or black, narrowly oblong, 2-4.5 × 0.7-2 mm. 2n = 42.
Biennial herb with a slender white taproot to 1 m tall Stem: upright, sometimes slightly branched. Leaves: alternate, long-stalked, 3 - 6 cm long and wide, lower leaves kidney-shaped, the rest triangular, pointed at the tip, and coarsely toothed. Having the odor of garlic when crushed. Flowers: in short, branched, terminal clusters, white or cream-colored, 5 - 7 mm long, and 3 mm wide. Petals four, with a narrowing base and rounded tip. Stamens six. Fruit: a narrow pod, pods widely spreading, 4 - 6.5 cm long, and four-angled. Seeds many, forming a single row in the pod, black, 3 mm long, and oblong.
Similar species: The alternate, long-stalked, broadly triangular, and coarsely toothed stem leaves help distinguish Alliaria petiolata from many other plants found in the Chicago Region. It is easily distinguished from all other woodland Brassicaceae by its small white flowers and odor of garlic made from crushing the leaves.
Flowering: mid-April to late July
Habitat and ecology: Introduced from Europe. This common weed spreads rapidly across vast areas of disturbed shaded ground, especially floodplains of streams. It also occurs in disturbed portions of moist woods and wood margins. It can become so abundant that it almost excludes the native vegetation.
Occurence in the Chicago region: non-native
Notes: First documented in the United States in 1868 in New York. The European settlers probably brought it here for cooking purposes (the garlic-flavored leaves are edible). It spread rapidly, and is now known to inhabit 38 states and four Canadian provinces. Management information for this important weed can be found at the Global Invasive Species Database (see link below).
Etymology: Alliaria means "of the Allium family." Allium comes from the Latin word for garlic. Petiolata means "furnished with a leaf stalk."
Biennial to 1 m, simple or little-branched, glabrous or with a few simple hairs; lower lvs reniform, the others deltoid, 3-6 cm long and wide, acute, coarsely toothed; pet 5-6 mm; mature pedicels stout, 5 mm; frs widely divergent, 4-6 cm; seeds black, 3 mm; 2n=42. Native of Europe, now found as a weed in gardens and moist woods throughout most of our range. May, June. (A. alliaria; A. officinalis)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Indiana Coefficient of Conservatism: C = null, non-native
Wetland Indicator Status: FAC
Diagnostic Traits: Winter annual or biennial to about 1 m tall; leaves petiolate, reniform to cordate, their margins sinuate-crenate; petals 4, white, 5-7 mm; fruits slender, erect or ascending siliques to 6 cm long.
Although not known for Indiana during Deam's time, the species is now a major invader of woodland habitat.