Plants perennial; often dioecious or monoecious; cespitose. Culms 2-7 m, erect, densely clumped. Leaves primarily basal; sheaths open, often overlapping, glabrous or hairy; auricles absent; ligules of hairs; blades to 2 m, flat to folded, arching, edges usually sharply serrate. Inflorescences terminal, plumose panicles, 30-130 cm, subtended by a long, ciliate bract; branches stiff to flexible. Spikelets somewhat laterally compressed, usually unisexual, sometimes bisexual, with 2-9 unisexual florets; disarticulation above the glumes and below the florets. Glumes unequal, nearly as long as the spikelets, hyaline, 1-veined; calluses pilose; lemmas 3-5(7)-veined, long-acuminate, bifid and awned or entire and mucronate; lemmas of pistillate and bisexual florets usually long-sericeous; lemmas of staminate florets less hairy or glabrous; lodicules 2, cuneate and irregularly lobed, ciliate; paleas about 1/2 as long as the lemmas, 2-veined; anthers of bisexual florets 3, 1.5-6 mm, those of the pistillate florets smaller or absent. Caryopses 1.5-3 mm; hila linear, about 1/2 as long as the caryopses; embryos usually shorter than 1 mm. x = 9. Name from the Spanish, cortada, cutting, referring to the sharply serrate blades.

Cortaderia, a genus of 24-25 species, is native to South America and New Zealand, with the majority of species being South American. Recent evidence suggests that the species in the two regions represent different lineages, each of which merits generic recognition. The species treated here would remain in Cortaderia if this change were made.

Both of the species that are found in North America were originally introduced as ornamental species; both are now considered aggressive weeds in parts of the Flora region.

A reference has been added.

1.   Cortaderia jubata (Lemoine ex Carrière) Stapf
Purple Pampas Grass

Plants pistillate (in North America). Culms 2-7 m, 4-7 times as long as the panicles. Leaves primarily basal; sheaths hairy, sometimes densely so; ligules 1-2 mm; blades 1 m long or longer, 2-10 cm wide, mostly flat, often horizontal, dark green, abaxial surfaces hairy near the base. Panicles 30-100 cm, elevated well above the basal foliage, deep violet when young. Spikelets 14-16 mm, pistillate; florets readily disarticulating; calluses about 0.6 mm; lemmas about 10 mm, long-attenuate to an awn, awns to 1 mm; paleas to 4 mm, keels ciliate, apical hairs extending beyond the body of the paleas; stigmas usually not exserted. Caryopses to 2.5 mm; embryos to 1 mm. 2n = 108.

Cortaderia jubata is found on the west coast of the coterminus United States, growing in disturbed, open ground such as brushy slopes, eroded banks and cliffs, road cuts, cut-over timber areas, and sand dunes. It is native to mountainous areas of Bolivia, Peru, and Ecuador. It was grown in the past as an ornamental because of its attractive panicles, but is now a serious weed in California, reproducing apomictically and invading many open habitats. It was mistakenly called Cortaderia rudiuscula Stapf by Hitchcock (1951). The florets of C. rudiuscula differ from those of C. jubata in being longer and narrower, having shorter, less hairy calluses, and in having no hairs that extend beyond the top of the palea. Cortaderia rudiuscula is not known from North America.

2.   Cortaderia selloana (Schult. & Schult. f.) Asch. & Graebn.
Pampas Grass

Plants usually dioecious, sometimes monoecious. Culms 2-4 m, usually 2-4 times as long as the panicles. Leaves primarily basal; sheaths mostly glabrous, with a dense tuft of hairs at the collars; ligules 1-2 mm; blades to 2 m long, 3-8 cm wide, mostly flat, cauline, ascending, arching, bluish-green, abaxial surfaces glabrous basally. Panicles 30-130 cm, only slightly, if at all, elevated above the foliage, whitish or pinkish when young. Spikelets 15-17 mm; calluses to 1 mm, with hairs to 2 mm; lemmas long-attenuate to an awn, awns 2.5-5 mm; paleas to 4 mm; stigmas exserted. Caryopses and florets not separating easily from the rachilla. 2n = 72.

Cortaderia selloana is native to central South America. It is cultivated as an ornamental in the warmer parts of North America. It was thought that it would not become a weed problem because most plants sold as ornamentals are unisexual, but it is now considered an aggressive weed in California and Bendigo, Australia. The weedy Australian plants are bisexual (Walsh 1994).