Cardaria pubescens (C. Meyer) Jarmol.
NOTE: This species is actionable only when found in field or vegetable seed for planting; tolerance applies.
Common names: hairy whitetop, globe-podded hoary cress
Fruit a 2-chambered silicle with 1–2 seeds per chamber, strongly inflated, spherical to ovoid, 3–4.5 mm tall, 2.5–4.5 mm broad, covered with short hairs.
Seeds elliptic to slightly obovate, with a notched, bluntly pointed base, (1.1)1.5–2.0 mm long, 1.0–1.5 mm wide, 0.5–0.7 mm thick, thickness +/– uniform, cross section oval. Testa dull, reddish-brown or purplish-red, sometimes with yellowish tinge. Faint groove or line runs from the base, gradually veering away from the margin and ending at about the middle of the seed. Surface minutely granular. Hilum in basal notch, inconspicuous, often hidden beneath funiculus or funicular material. Embryo bent, cotyledons incumbent, radicle same length as cotyledons; endosperm nearly absent.
The seeds of the three species of Cardaria — C. chalepensis, C. draba, and C. pubescens — may be distinguishable if they are well developed. If immature, they may be indistinguishable. For example, the degree of redness may vary with conditions of development. The silicles of the three species, however, are quite distinct.
Cardaria chalepensis (L.) Hand.-Mazz.
Cardaria draba (L.) Desv.
Mature seed characteristics:
Cardaria draba: darker reddish brown than C. pubescens and C. chalepensis.
Cardaria draba and Cardaria chalepensis: cotyledon edge thicker than radicle edge.
Cardaria pubescens: more broadly elliptic, flatter, smoother than C. draba and C. chalepensis; thickness uniform throughout.
Asia: China, Kazakhstan, Mongolia, Western Siberia; North America: Canada, United States.
Native to temperate Asia.
Temperate, ranging from cold, subalpine regions to arid environments; tolerates wide range of soil types and moisture conditions; a weed of wildlands, disturbed open sites, field crops, orchards, pastures, roadsides, neglected areas.
Cardaria pubescens is a deep-rooted perennial herb up to 0.5 m tall. Seed production is prolific, but this species is an aggressive weed primarily because of its extensive horizontal and vertical root and shoot network. New shoots arise from buds on lateral underground shoots or shoot fragments. Both seeds and shoot fragments in mud or soil can be carried by livestock, farm equipment, and streams. Cultivation can facilitate spread by creating shoot fragments. Cardaria pubescens rapidly establishes dense stands that crowd out forage plants and native vegetation. It has become a major weed of crops in Europe and the Middle East, and of cereal crops in the U.S., particularly in the western states. This species often occurs with C. draba and C. chalepensis in Canada. Cardaria pubescens is one of ten species covered under the Federal Seed Act for which tolerance is applicable to its introduction (7 CFR 361.6(a)(2)).