Sevenangle Pipewort

The name Eriocaulon septangulare Withering, widely used for this species, is invalid (H. N. Moldenke 1937). Some (T. G. Tutin et al. 1964--1980, vol. 5) retain E. aquaticum (Hill) Druce as the valid name if one accepts both North American and European plants as the same species (the alternative taken here). If North American plants are considered to be distinct from Eurasian ones, then the appropriate binomial for ours becomes E. pellucidum Michaux.

Herbs, perennial, 4--21 cm (--100 cm when submersed). Leaves linear-attenuate, 1--10 cm (--40 cm when submersed), apex often subulate. Inflorescences: scape sheaths longer (shores) or shorter (submersed) than principal leaves, inflated; scapes linear to filiform, 1 mm wide, (4--)5--7-ribbed; mature heads white to pale gray, young heads dark, hemispheric to globose, 4--10 mm wide, soft, flattened when pressed; receptacle glabrous or rarely with a few clear hairs; involucral bracts becoming reflexed, obscured by proximal bracts and flowers, dark gray, broadly oblong to narrowly ovate or broadly obovate, 1--1.5 mm, margins entire, apex rounded, abaxially with white, club-shaped hairs, otherwise glabrous; inner and receptacular bracts gray to near black, oblanceolate or cuneate, 1.5 mm, margins entire, apex acute, distal margins and abaxial apical surface with white, club-shaped hairs. Staminate flowers: sepals 2, grayish, oblong-linear or linear-oblanceolate, curved, 1.5 mm, apex acute to rounded, margins and abaxial surface with white, club-shaped hairs; androphore club-shaped; petals 2, triangular, nearly equal, 0.5 mm, ciliate, hairs white, club-shaped; stamens 4; anthers black. Pistillate flowers: sepals 2, gray, oblong to narrowly obovate, curved, keeled, 1.5 mm, blade usually ciliate, distal abaxial surfaces with white hairs; petals 2, pale, oblong-linear to linear oblanceolate, 1.5 mm, apex acute to obtuse, apically ciliate, adaxially with white, club-shaped hairs; pistil 2-carpellate. Seeds light brown or red-brown, ovoid to broadly ellipsoid, 0.5 mm, very faintly reticulate, not papillate.

N.B., Nfld. and Labr. (Nfld.), N.S., Ont., Que., Ala., Conn., Del., Ind., Maine, Md., Mass., Mich., Minn., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., Vt., Va., Wis.; Europe (Great Britain, Ireland).

Flowering spring--fall.

Sandy or peaty, often sphagnous, shores, bogs, muskegs, shallows; 0--600m.

Cespa aquatica Hill, Herb. Brit., 96*, plate 66 bis. 1769; Eriocaulon articulatum (Hudson) Morong; E. pellucidum Michaux; E. pumilum Rafinesque; Nasmythia articulata Hudson; N. septangularis (Withering) Martius

Eriocaulon septangulare With. Veg. Brit. 784. 1776
?Cespa aquatica Hill, Herb. Brit. pi. 66. 1769. Nasmythia articulata Huds. Fl. Angl. ed. 2. 415. 1778. Eriocaulon pellucidum Michx. Fl. Bor. Am. 2: 166. 1803. Eriocaulon pumilum Raf. Atl. Jour. 121. 1832.
Nasmythia septangularis Mart. Nova Acta Acad. Leop. -Carol. 17: 58, pi. 2,f. 2. 1835. Eriocaulon articulatum Morong, Bull. Torrey Club 18: 353. 1891.
Eriocaulon aquaticum Druce, Pharm. Jour. IV. 29: 700. 1909. Not E. aquaticum Sagot, in syn. 1863.
Plants monoecious; stems very short; leaves tufted, thin-membranous or mostly pellucid, linear, plane, 1-18 (mostly 2-6) cm. long, 1-3.5 mm. wide at the middle, subulate-acute, fenestrately 3-8-nerved (the fenestrations conspicuous), glabrous; peduncles mostly solitary (rarely aggregate), 3.5-56 cm. long (to 3 m. long in deep water, according to Britton), 7-sulcate, usually not twisted, compressed in drying, mostly fenestrate, glabrous; heads hemispheric, loose-flowered, 3-5 mm. in diameter, compressed in drying, whitevillose at the summit ; involucral bractlets thin-membranous, gray-green or olivaceous, ovate or obovate, mostly rounded-obtuse, glabrous; receptacle glabrous; receptacular bractlets membranous, hyaline at base, grayish at apex, cuneate-obovate, acute or acuminate, pilose on the back toward apex; staminate florets: sepals 2, free, grayish, cuneate-spatulate, concave-navicular, more or less obtuse, very narrowly carinate-winged, puberulent at apex on the back or finally calvescent; petal-tube white, its lobes 2, pale-stramineous, equal, pilose, glanduliferous; pistillate florets: sepals 2, nigrescent (hyaline at base), cuneate-obovate, concave, truncate, slightly apiculate, very narrowly carinate-winged, pilosulous at apex on the back; petals 2, whitish, spatulate, obtuse, pilose, glanduliferous, equal when young, subequal when mature.
Type locality: In lakes on the Island of Skye, Scotland (Walker).
Distribution: In still water and on shores of ponds, Newfoundland to New Jersey, and westward to Ontario, Minnesota, and Indiana; also in the Hebrides and adjoining islands of northern Scotland and Ireland.

Eriocaulon aquaticum is a species of flowering plant in the family Eriocaulaceae.

It is known by many common names such as the common pipewort, northern pipewort, seven-angled pipewort or hatpins.