Flowers perfect. Petals imbricated in the bud. Stamens 6–21 or more. Ovaries several or many, imbricated in a head, forming thick and ribbed achenes in fruit, often beaked with a projecting persistent style.—Mostly annuals, with the habit of Sagittaria, the naked stems sparingly branched or simple, and the flowers on rather short pedicels, in whorls of 3–6 or more. Fl. summer and autumn. (Name from ἐχινώδης, prickly, or from ἐχῖνος, and δορός a leathern bottle, applied to the ovary, which is in most species armed with the persistent style, so as to form a sort of prickly head of fruit.)
1. E. párvulus, Engelm. Scapes 1–3´ high; shoots often creeping and proliferous; leaves lanceolate or spatulate, acute (½–1½´ long, including the petiole); umbel single, 2–8-flowered; pedicels reflexed in fruit; flower 3´´ broad; stamens 9; styles much shorter than the ovary; achenes beakless, obtusely few-ribbed.—In mud, Mass. to Mich. and E. Minn., south to Fla. and Tex. (S. Am.)
2. E. rostràtus, Engelm. Scape erect, 3´–2° high, longer than the leaves; leaves broadly ovate, cordate or truncate at base, obtuse (the blade 1–3´ long); umbel proliferous, in a branched panicle; flower 5´´ broad; stamens 12; styles longer than the ovary; achenes beaked, acutely many-ribbed.—Swamps and ditches, Ill. to Fla., Mo., and Tex.—A low form (var. lanceolàtus, Engelm.) has the leaves lanceolate with an acute base. Ill., Mo.
3. E. radìcans, Engelm. Stems or scape prostrate, creeping (2–4° long), proliferous, bearing many whorls of flowers; leaves somewhat truncately broadly heart-shaped, obtuse (2–8´ broad), long-petioled; flowers 6–9´´ broad; stamens about 21; styles shorter than the ovary; achenes short-beaked, the keeled back denticulate.—Swamps, Ill. to N. C. and Fla., west to Mo. and Tex.
Order 126. NAIADÀCEÆ. (Pondweed Family.)
Marsh or mostly immersed aquatic herbs, with stems jointed and leafy or (in Triglochin) naked and scape-like, leaves sheathing at base or stipulate, and flowers perfect or unisexual, often spathaceous, with perianth of 4 or 6 herbaceous distinct valvate segments, or membranous and tubular or cup-shaped, or none. Stamens 1, 2, 4 or 6, with extrorse anthers. Ovaries 1–6, distinct or more or less coherent, 1-celled, usually 1-ovuled, in fruit follicular or capsular or an indehiscent berry or utricle.
Suborder I. Juncagineæ. Marsh plants, with terete bladeless leaves; flowers perfect, spicate or racemose, with herbaceous 6- (rarely 3-) lobed perianth; carpels 3 or 6, more or less united, separating at maturity. Seeds anatropous; embryo straight.
1. Triglochin. Ovaries 3–6, united until maturity. Leaves radical. Flowers bractless, in a spike-like raceme terminating a jointless scape.
2. Scheuchzeria. Ovaries 3, nearly distinct, at length divergent. Flowers bracteate in a loose raceme upon a leafy stem.
Suborder II. Naiadeæ. Immersed aquatics, with flat leaves; ovaries solitary or distinct, 1-ovuled.