Microthlaspi perfoliatum (L.) F.K. Mey.

Penny Cress

Microthlaspi perfoliatum plant

Family - Brassicaceae

Stems - To +30cm tall, glabrous, glaucous, herbaceous, erect or branching above, from long taproot.

Leaves - Basal leaves in rosette, petiolate. Petiole to 2cm long, glabrous. Blade to 3cm long, 1.5cm wide, ovate, elliptic or oblong, glabrous, coarsely toothed. Cauline leaves clasping, auriculate, glabrous, glaucous, entire to coarsely toothed, reduced upward.

Microthlaspi perfoliatum leafLeaf, not truly perfoliate

Microthlaspi perfoliatum leavesCauline and basal leaf respectively.

Inflorescence - Terminal raceme. Compact in flower, becoming elongated in fruit to +10cm. Pedicels to 4mm long in flower, expanding in fruit to 6mm, filiform, glabrous.

Microthlaspi perfoliatum inflorescence

Microthlaspi perfoliatum inflorescenceInflorescence top view

Flowers - Petals 4, white, glabrous, spatulate to oblanceolate, to 2.5mm long, 1mm broad. Stamens 6, didynamous. Filaments 1.2mm long, glabrous, white. Anthers yellow, .2mm long. Style 1, very short, to .2mm long. Ovary green, superior, compressed, ovoid to rotund, 1mm long. Sepals 4, distinct, to 1.5mm long, 1mm broad, green with whitish margins, subacute at apex, ovate-oblong. Silicle to 6mm long, winged, obcordate, notched at apex, glabrous.

Microthlaspi perfoliatum flowerFlower close-up.

Microthlaspi perfoliatum calyxCalyx close-up.

Microthlaspi perfoliatum fruitFruit close-up.

Flowering - March - May.

Habitat - Roadsides, waste ground, rocky outcroppings and open ground.

Origin - Native to Europe.

Other info. - Yet another one of the introduced plants from the Brassicaceae which dominate the early springtime. The stems of this plant appear to pass through the leaves, hence the name "perfoliatum" from "perfoliate." In truth, the leaves are not perfoliate but instead merely strongly clasp the stem, bearing prominent auricles. "Thlaspi" comes from the Greek name of cresses - "thlaspis" - with "micro" denoting a diminutive form.
This plant is common and locally quite abundant. The fruits slightly resemble those of Capsella bursa-pastoris (L.) Medic. but the latter has fruits which are more triangular in shape and are smaller when mature. The leaves of both plants differ greatly from one another.

Photographs taken at Eagle Bluffs Conservation Area, Boone County, MO., 3-7-04 (DETenaglia); also near Labadie, Franklin County, MO, 3-30-2015 (SRTurner).