Arabidopsis thaliana (L.) Heyn. - Rock Cress
Family - Brassicaceae
Stems - To +35cm tall, freely branching, single or multiple from the base, hirsute basally, becoming glabrous apically, glaucous, from a taproot, green and often with some purple at the nodes.
Leaves - Alternate. Basal leaves in a rosette, spatulate, petiolate, entire or shallowly dentate, to +/-7cm long, 2cm broad, with forked trichomes above and below, rounded at the apex. Cauline leaves alternate, sessile, to 2.5cm long, 7-8mm broad, entire, ciliate-margined and with some forked trichomes above and below, oblong, rounded at the apex, few (2-6 per stem).
Inflorescence - Terminal and axillary racemes, compact in flower, elongated in fruit to +15cm long. Pedicels to 1cm long in fruit, filiform, glabrous and glaucous.
Flowers - Petals 4, white, glabrous, spatulate, to 4mm long, 1.2mm broad, rounded at the apex. Stamens 6, erect. Filaments white, glabrous, 2.5mm long. Anthers yellow, .3mm long. Ovary cylindric, green, glabrous, superior, 2mm long in fruit. Style wanting. Sepals 4, green, glabrous internally, with a few cilia externally, 1.5mm long, .8mm broad, green, cupped, subulate, with margins slightly scarious near the apex. Siliques to +/-1.5cm long, .8mm in diameter, mostly terete, glabrous, many-seeded, beaked. Beak to .5mm long.
Flowering - April - May.
Habitat - Open sandy ground, rocky open ground, fallow fields, pastures, waste ground, roadsides, railroads.
Origin - Native to Europe.
Other info. - This small species can be found mostly in the southern half of Missouri. The plant is fairly indistinct but can be identified by its thin siliques, small white flowers, basal rosette, and hairy (near the base) stems. A. thaliana is used widely in experiments on plants because it short-lived and grows very quickly.
Photographs taken in Brown Summit, NC., 3-13-03, and 4-6-03, and in Auburn, AL., 2-19-05.