Plants annual; synoecious. Culms 1-75 cm, erect to geniculately ascending, sometimes branching above the base; nodes usually exposed. Sheaths open, often becoming inflated, junction with the blades evident; ligules of hairs; auricles absent; blades often disarticulating. Inflorescences terminal or terminal and axillary, spikelike or capitate panicles subtended by, and often partially enclosed in, 1 or more of the uppermost leaf sheaths, additional panicles often present in the axils of the leaves below. Spikelets 2-6 mm, strongly laterally compressed, with 1 floret; florets bisexual; disarticulation above or below the glumes. Glumes 1-veined, strongly keeled; lemmas membranous, glabrous, 1-veined, strongly keeled, not lobed, unawned, sometimes mucronate; paleas hyaline, 1-2-veined; lodicules absent; anthers 2 or 3; ovaries glabrous. Fruits oblong, pericarp loosely enclosing the seed and easily removed when wet; hila punctate. x = 8. Name from the Greek krupsis, concealment, alluding to the partially concealed inflorescence.

Crypsis, a genus of eight species, is native from the Mediterranean region to northern China. Its species tend to occur in moist soils, often in areas subject to winter flooding. The three species found in the Flora region are very plastic in the lengths of their culms and leaves, e.g., the culms of C. schoenoides vary from 2 cm in dry sites to 75 cm under optimal conditions.

1.   Crypsis alopecuroides (Piller & Mitterp.) Schrad.
Foxtail Pricklegrass

Culms (3)5-75 cm, rarely branched above the base. Sheaths glabrous; collars glabrous; ligules 0.2-1 mm; blades 5-12 cm long, 1.2-2.5 mm wide, not disarticulating. Panicles 1.5-6.5 cm long, 4-6 mm wide, 7-8 times longer than wide, often purplish, completely exserted from the uppermost sheath at maturity on peduncles at least 1 cm long. Spikelets 1.8-2.8 mm, remaining lightly attached until late in the season. Lower glumes 1.2-2 mm; upper glumes 1.4-2.4 mm; lemmas 1.7-2.8 mm; paleas faintly 2-veined; anthers 3, 0.5-0.6 mm. Caryopses 0.9-1.1 mm. 2n = 16.

Crypsis alopecuroides is common to abundant in sandy soils around drying lake margins in Oregon and southern Washington, and within the last forty years has become widespread in northern California; it is also known from several other western states. It was first collected in the Western Hemisphere in the late 1800s from shipyard areas in and around Philadelphia, but has not been collected in the eastern United States since. In the Eastern Hemisphere, it extends from France and northern Africa to the Urals and Iraq.

2.   Crypsis schoenoides (L.) Lam.
Swamp Pricklegrass

Culms 2-75 cm, prostrate to erect, sometimes geniculate, usually not branching above the base, but some plants profusely branched. Sheaths glabrous or ciliate at the throat, often inflated; collars glabrous; ligules 0.5-1 mm; blades 2-10 cm long, 2-6 mm wide, not disarticulating. Panicles 0.3-4(7.5) cm long, 5-6(15) mm wide, 1-5 times longer than wide, bases usually enclosed in the uppermost leaf sheaths at maturity. Spikelets 2.7-3.2 mm, tardily disarticulating. Lower glumes 1.8-2.3 mm; upper glumes 2.2-2.7 mm; lemmas 2.4-3 mm; paleas 2-veined; anthers 3, 0.7-1.1 mm. Caryopses about 1.3 mm. 2n = 32.

Crypsis schoenoides is common to abundant in clay or sandy clay soils around drying lake margins and vernal pools. In the Flora region, it is most abundant in California, but also appears to be established in a few other western states. It is known from a few collections in several eastern states (where it was first introduced in the late 1800s), though apparently none more recently than 1955. Its native range extends from southern Europe and northern Africa through western Asia to India.

3.   Crypsis vaginiflora (Forssk.) Opiz
Modest Pricklegrass

Culms 1-30 cm, often profusely branching above the base, with 10-25 panicles per culm. Sheaths pilose on the margins; collars pilose; blades 1-5 cm long, 1-3 mm wide, soon disarticulating, thus many leaves on mature plants are bladeless. Panicles 0.3-1.5(3.5) cm long, 3-6(10) mm wide, 1-5 times longer than wide, sessile or almost so, mostly included in the sheaths of the upper 2 leaves. Spikelets 2.5-3.2 mm, readily disarticulating when disturbed, otherwise retained within the upper sheaths. Glumes about 3 mm, subequal; lower glumes pilose on the margins; lemmas subequal to the glumes; paleas minutely 2-veined; anthers 3, 0.5-0.9 mm. Caryopses 1.3-1.7 mm. 2n = 48.

Crypsis vaginiflora is common to abundant in clay or sandy clay soil in California, where it was first introduced in the late 1800s. It has since been found at a few locations in Washington, Idaho, and Nevada, and will probably spread to additional sites with suitable habitat in the future. It is native to Egypt and southwestern Asia.