Thlaspi alliaceum L.

Garlic Mustard

Thlaspi alliaceum plant

Family - Brassicaceae

Stems - To +60cm tall, multiple from the base, from a taproot, erect, herbaceous, with pilose hairs near the base, glabrous and glaucous above, slightly ribbed near the base, with a garlic odor when bruised or crushed.

Thlaspi alliaceum stemLower stem.

Thlaspi alliaceum stem
Middle stem and leaves.

Leaves - Alternate, sessile, auriculate, clasping, to 4cm long, 1.5cm broad, shallow-irregular dentate, oblong, glabrous. Auricles pointed.

Thlaspi alliaceum leaves

Inflorescence - Terminal and axillary racemes, compact in flower, greatly elongating in fruit. Pedicels to 5mm long in flower, quickly elongating and spreading in fruit to 1.3cm long, glabrous.

Thlaspi alliaceum inflorescence

Flowers - Petals 4, white, 2mm long, 1mm broad at the apex, tapering to the base, glabrous, blunt at the apex. Stamens 6, erect. Filaments greenish, to 1.2mm long, glabrous. Anthers yellow, .2mm long. Ovary superior, green, rotund, 1mm in diameter, glabrous. Style short, thick, .2mm long. Sepals green, glabrous, rounded at the apex, shorter than the petals, erect to spreading, cupped. Silicles to 6mm long, 3-4mm broad, slightly winged, 2-valved (valves separated by a scarious septum), green, glabrous, with a shallow notch at the apex. Seeds 2-4 per locule , rugose to reticulate, to -2mm long, dark brown when mature.

Thlaspi alliaceum calyxCalyces.

Thlaspi alliaceum flowersCorollas.

Thlaspi alliaceum fruitFruits.

Flowering - April - May.

Habitat - Wet fields, roadsides, disturbed flood plains.

Origin - Native to Eurasia.

Other info. - This species is rare in Missouri and can only be found in possibly a handful of counties. The plant was first cataloged in North America in the early 1960s in North Carolina. In the past three decades it has spread through much of the eastern United States and as far south as Louisiana. Platte County, MO. is the most western report of the plant thus far in the U.S.
The plant can be identified because of its long fruiting inflorescences, its inflated and only narrowly winged fruits, and its garlic odor when crushed. Fields with lots of this plant present are redolent of garlic.

Photographs taken at the Dr. Frederick Marshall Conservation Area, Platte County, MO., 5-6-01, and in Reidsville, NC., 3-23-03 (DETenaglia); also near Morse Mill, Jefferson County, MO, 4-20-2015 (SRTurner).