Whorl Grass

In Great Britain and/or Ireland:
Foodplant / parasite
Sorosphaeria radicalis parasitises live root hair of Catabrosa aquatica

Catabrosa aquatica is a widespread, polymorphic species of aquatic and marshy habitats, and extreme forms are sometimes accorded separate status, either at specific or infraspecific rank.

This species provides good forage.

An aquatic grass with sweet stems and succulent foliage eagerly sought by cattle. Smaller plants with panicles about 6 cm long and purple spikelets have been separated as Catahrosa sikkimensis, but such variants occur sporadically throughout the range of Catahrosa aquatica and are of little taxonomic consequence. Another variant, even less well-marked, has shorter panicle branches (up to 5 cm) and smaller lemmas (1.5-1.7 mm long). It is sometimes separated as var. angusta.

Perennial, rhizomatous; rhizome stout, creeping. Culms erect, succulent, 20–70 cm tall, unbranched. Leaf sheaths closed up to middle, upper shorter than internodes; leaf blades equally wide throughout, soft, 5–20 cm × 2–8 mm, apex boat-shaped; ligule 2–5 mm, obtuse. Panicle open or loosely contracted at anthesis, ovate to oblong in outline, 10–30 × 4–12 cm; branches whorled, slender, usually obliquely ascending, up to 10 cm, often bare of spikelets in lower part. Spikelets with (1–)2(–3) florets, 2–4(–5.8) mm; glumes obtuse or subtruncate; lower glume ovate to suborbicular, 0.5–1.2(–2) mm; upper glume broadly elliptic, 1–2(–3) mm; lemma 1.5–3 mm, green becoming brown at maturity, usually glabrous, apex truncate. Anthers 1–2 mm. Fl. and fr. Apr–Aug. 2n = 20.

Stoloniferous perennial; cuhms 5-70 cm high, erect or geniculately ascending, slender to somewhat stout, succulent, smooth. Leaf-blades 4-20 cm long, 2-10 mm wide, rather thin. Panicle ovate to oblong, 5-30 cm long, 2.5-10 cm wide, the branches in half whorls of 3-5, successive whorls alternating. Spikelets 3-5 mm long, breaking up at maturity between the lemmas, green, yellow or brown, often variegated with purple; glumes obovate, blunt, the lower 1-1.5 mm long, the upper 1.5-2.5 mm long; lemma (1.5-)2.5-3.5 mm long, smooth or with minute hairs on the nerves.

Gansu, Guizhou, Hebei, Hubei, Nei Mongol, Qinghai, Sichuan, Xinjiang, Xizang, Yunnan [Afghanistan, Kashmir, Kazakhstan, Kyrgyzstan, Mongolia, Pakistan, Russia, Tajikistan, Turkmenistan; SW Asia, Europe, North America].

Distribution: Pakistan (Baluchistan & Kashmir); throughout the range of the genus.

Slow-moving, shallow water of river and streamsides, muddy pond margins, ditches; 800–4000 m.

Perennials, Aquatic, leaves emergent, Terrestrial, not aquatic, Rhizomes present, Rhizome elongate, creeping, stems distant, Stolons or runners present, Stems trailing, spreading or prostrate, Stems nodes swollen or brittle, Stems erect or ascending, Stems geniculate, decumbent, or lax, sometimes rooting at nodes, Stems mat or turf forming, Stems terete, round in cross section, or polygonal, Stem internodes hollow, Stems with inflorescence less than 1 m tall, Stems, culms, or scapes exceeding basal leaves, Leaves mostly basal, below middle of stem, Leaves mostly cauline, Leaves conspicuously 2-ranked, distichous, Leaves sheathing at base, Leaf sheath mostly closed, Leaf sheath smooth, glabrous, Leaf sheath and blade differentiated, Leaf blades linear, Leaf blades 2-10 mm wide, Leaf blades mostly flat, Leaf blade margins folded, involute, or conduplicate, Leaf blades mostly glabrous, Ligule present, Ligule an unfringed eciliate membrane, Inflorescence terminal, Inflorescence an open panicle, openly paniculate, branches spreading, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence a panicle with narrowly rac emose or spicate branches, Inflorescence branches more than 10 to numerous, Flowers bisexual, Spikelets pedicellate, Spikelets sessile or subsessile, Spikelets laterally compressed, Spikelet less than 3 mm wide, Spikelets with 2 florets, Spikelets solitary at rachis nodes, Spikelets all alike and fertille, Spikelets bisexual, Spikelets disarticulating above the glumes, glumes persistent, Spikelets disarticulating beneath or between the florets, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes distinctly unequal, Glumes shorter than adjacent lemma, Glumes 1 nerved, Lemmas thin, chartaceous, hyaline, cartilaginous, or membranous, Lemma coriaceous, firmer or thicker in texture than the glumes, Lemma 3 nerved, Lemma glabrous, Lemma apex truncate, rounded, or obtuse, Lemma awnless, Lemma margins thin, lying flat, Lemma straight, Palea present, well developed, Palea membranous, hyaline, Palea about equal to lemma, Palea longer than lemma , Palea 2 nerved or 2 keeled, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis.

Catabrosa aquatica, called brookgrass, water whorl-grass, water whirlgrass and water hairgrass, is a widespread species of semi-aquatic grass in the genus Catabrosa, native to the most of the non-tropical northern hemisphere, and to southern Chile and Argentina. As its scientific and common names suggest, it prefers to grow in wet areas, such as meadows, stream banks and lake shores.