2. Arabidopsis thaliana (L.) Heynh. (mouse-eared cress, thale cress)
Pl. 311 a, b; Map 1313
Plants annual, terrestrial. Stems (2–)5–30(–50) cm
long, erect or ascending, branched or unbranched below the inflorescence, often
glabrous in the apical half, pubescent toward the base with mostly unbranched
hairs intermixed with 2- or 3-branched stalked hairs. Leaves mostly basal,
those of the stems alternate, 1–5 cm long, sessile or the leaf blades
narrowed to short petioles, the bases not clasping. Leaf blades oblong to
spatulate, progressively reduced and narrowed to linear toward the stem tip,
the margins entire or with few shallow teeth, sparsely to densely pubescent
with unbranched, forked, and/or rarely 2- or 3-branched stalked hairs.
Inflorescences panicles or racemes. Sepals 1.0–2.0(–2.5) mm
long, ascending, oblong, hairy. Petals 2.0–3.5 mm long, unlobed, white.
Styles 0.1–0.5 mm long. Fruits spreading to ascending, straight or
nearly so, (0.8–)1.0–1.8 cm long, to 20 times as long as wide,
circular in cross-section, not beaked, each valve with a midnerve. Seeds in 1
row in each locule, 0.3–0.5 mm long, oblong in outline, the surface
with a fine, netlike or honeycomb-like pattern of ridges and pits to nearly
smooth, orange. 2n=10. April–May.
Introduced, scattered in eastern and southern Missouri
(native of Europe and Asia, widely naturalized
in temperate areas of the world). Disturbed ground in pastures, fallow fields,
lawns, waste areas, railroads, and roadsides.
Arabidopsis thaliana is an inconspicuous weed of disturbed areas. In
recent years, however, it has become an extremely important tool in scientific
studies on various aspects of plant physiology, biochemistry, pathology,
ecology, development, and genetics. As a laboratory organism, it has the
advantages of relatively few chromosomes, a relatively simple genetic system, a
short life cycle that can be completed in a few weeks, and small plant size,
making it amenable to cultivation in greenhouses, growth chambers, and in test
tubes under sterile conditions.