1. Thlaspi alliaceum L. (roadside penny cress)

Map 1394

Plants with a strong smell of garlic when crushed, often glaucous. Stems 20–60(–80) cm long, pubescent near the base. Leaves 1–5 cm long, narrowly elliptic to oblong or ovate, sessile, the basal auricles pointed, the margin toothed, the basal leaves few or absent at flowering time. Sepals 1–2 mm long. Petals 2.5–4.0(–5.0) mm long. Styles 0.2–0.3 mm long. Fruits 5–10 mm long, obovate, inflated, narrowly winged below, slightle more broadly winged above, the apical notch shallow. Seeds mostly 3–5 per locule, 2–4 mm long, broadly ellipsoid, the surface with a netlike or honeycomb-like pattern of ridges and pits, dark brown to black. 2n=14. March–May.

Introduced, uncommon, known thus far from a single specimen from Platte County (native of Europe; introduced sporadically in the northeastern U.S. and Louisiana). Disturbed floodplains of rivers.

This species was first reported for Missouri by Tenaglia and Yatskievych (2002). As noted by them, the species was first collected in the United States in the early 1960s in North Carolina. It has spread quickly and is expected to be found elsewhere in Missouri in the future.