Thlaspi arvense field penny-cress; stinkweed Brassicaceae THAR*; Bx, pb; Q, j, wl; K, p; R, hs;

 

Thlaspi arvense.commons.wikimedia.org

Thlaspi arvense.commons.wikimedia.org (Accessed 11/2014).

Thlaspi arvense is an annual or winter annual herb, to 60 cm tall (usually much less), odor unpleasant, stem smooth, often unbranched. 

Leaves alternate, winter rosette leaves entire, stalked, soon deciduous, upper leaves thin, stalkless (sessile), narrow, clasping stem, with small, narrow lobes at base, margin often toothed. 

Flowers white, 0.3 cm wide, 4-parted, stamens 6, 2 short, 4 long, in elongating raceme; self-fertile (autogamous) (Mulligan and Kevan 1973) but visited by bees such as Andrena forbesii, Dialictus lineatulus, and flies, including several species of Eristalis and Helophilus; blooms April-June; mostly self-pollinating (Warwick et al. 2002). 

Thlaspi arvense.fruit.Thlaspi arvense. By Arthur Haines. Copyright © 2017.New England Wild Flower Society.gobotany.newenglandwild.org

Thlaspi arvense.fruit.Thlaspi arvense. By Arthur Haines. Copyright © 2017.New England Wild Flower Society.gobotany.newenglandwild.org (Accessed 3/2017).

Fruit dry, about 1.5 cm, circular, flattened and winged all around, with a seam (septum) from deeply notched tip to base, becoming yellowish, on upward-curving stalks; seeds dark, 5-8 per side (locule), ca 0.2 cm each, fruits in July. Plants produce an average of 900 to over 7, 000 seeds (Best and McIntyre 1975; Uva et al. 1997). Winter plant retains flat, silvery fruit husks (personal observation). Seeds viable in soil for over 20 years (Warwick et al. 2002). 

Wetland status: NI (USDA NRCS 2010). 

Frequency in NYC: Infrequent. 

Origin: Europe.

Habitat: A pioneer species and agricultural weed (Warwick et al. 2002) of open, disturbed soil in lawns, roadsides, and fill. 

Notes: Seeds yield the mustard oil allyl isothiocyanate, when the glucoside sinigrin is broken down (Kingsbury1964); producing a garlic-like small when crushed (Warwick et al. 2002). Seeds germinate both in early spring and in autumn, flowering occurs within 50 days of spring germination. Seeds viable in soil for 10-20 years (Best and McIntyre 1975). Listed as invasive or noxious by several sources (USDA, NRCS 2010). Seeds eaten by birds, plants eaten by few if any insects, but infected by some fungi (Warwick et al. 2002)