Flora of North America species comparison

taproots or fibrous, and then often with adventitious nodal roots;

rhizomes sometimes present [stolons in some Haloragis].

absent.

delicate, often branched, to 1 m, with numerous black, ascidiate trichomes.

erect, ascending, decumbent, or prostrate, cylindric to 4-ribbed, glabrous or scabrous to pubescent, hairs uniseriate and multiseriate, glands present or absent.

present, green to brown, very narrowly cylindrical, with gradual and moderate transition from foliage leaves to slightly reduced turion leaves, to 10 cm, apex ± rounded;

leaves pectinate and stiff, strongly appressed to axis, elliptic to narrowly obovate in outline, 11–23(–40) × 1.5–3(–4) mm;

segments 6–12(–14), longest segment (1.5–)3–5.5 mm, basal segment less than or equal to 2/3 central axis of leaf, apex acute; brown, ascidiate trichomes scattered on surfaces and in axils.

present or absent, lateral and/or terminal.

all submersed, usually in whorls of 3(or 4), sometimes alternate or subverticillate, homomorphic;

petiole 0–3 mm;

leaves pectinate, ovate to elliptic or obovate in outline, (6–)10–20(–25) × (4–)7–15 mm, segments (7–)10–14(–16), linear-filiform, longest segment (4–)8–15(–22) mm, with black ascidiate trichomes scattered on surfaces and in axils.

opposite, alternate, or subverticillate to whorled, simple, often heteromorphic in Myriophyllum and Proserpinaca;

stipules absent;

sessile or petiolate;

blade lobed, unlobed, or pinnatifid to pectinate, margins entire or serrate, surfaces glabrous or scabrous.

submersed, to 30 cm;

flowers bisexual;

bracteoles cream, trullate, 0.2–0.5(–0.8) × (0.1–)0.3–0.5 mm, margins entire or irregularly lobed, lobes with glandular fringe.

terminal or lateral in axils of bracts or leaves, determinate or indeterminate, dichasia (Haloragis and Proserpinaca), or simple racemes (Myriophyllum);

bracts and bracteoles present.

bisexual or unisexual, staminate and pistillate usually on same plant, sessile or pedicellate (sometimes sessile in pistillate flowers of Myriophyllum);

perianth and androecium epigynous;

hypanthium subglobose;

sepals persistent, (3 or)4, sometimes rudimentary (Myriophyllum), petals often caducous, sometimes persistent, (3 or)4, or 0 or rudimentary (Proserpinaca), keeled, cucullate, often distally cupulate;

stamens 3–8 (1 or 2 times as many as sepals);

anthers basifixed, dehiscing longitudinally;

pistil 1, 3- or 4-carpellate;

ovary 1, inferior, 1–4-locular;

placentation axile;

styles 1 per locule;

stigmas 1 per locule, clavate, capitate, fimbriate;

ovules 1(or 2, in Haloragis and Proserpinaca), anatropous, bitegmic, crassinucellate.

sepals green to cream or ± purple, ovate to trullate, 0.1–0.5(–0.7) × 0.1–0.3(–0.5) mm;

petals persistent, cream to purple, elliptic to obovate, 0.6–1.3 × 0.3–0.8 mm;

stamens 4, filaments to 0.5 mm, anthers 0.2–0.4 × 0.1–0.3 mm;

pistils 0.8–1.2 × 0.2–0.3 mm, stigmas red to ± purple, to 0.5 mm.

cylindric to subglobose, deeply 4-lobed.

a nutlet, indehiscent, or schizocarp, splitting into (2–)4 mericarps;

exocarp glabrous, scabrous, rugose, tuberculate, or papillate, sometimes with ribs, ridges, or wings.

1 per locule;

embryo straight, cylindric;

endosperm ± copious and fleshy.

tan to brown, cylindric, (1–)1.5–2.5 × 0.5–0.9 mm, transversely hexagonal (rounded to obtusely angled adaxially), abaxial surface shallowly 4-angled, smooth or sparsely tuberculate, with 4 longitudinal ridges, ridges with irregular, shallow to pronounced, membranous wings, ribs absent.

= 14.