Myriophyllum heterophyllum

Michaux

Fl. Bor.-Amer. 2: 191. 1803.

Common names: Two-leaf or various-leaved water-milfoil myriophylle à feuilles variées
Treatment appears in FNA Volume 10.
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Herbs monoecious, aquatic, often forming dense stands. Stems often branched, to 2.5 m. Turions absent. Leaves usually in whorls of 4 (–6), often subverticillate, sometimes alter­nate, heteromorphic; petiole to 5 mm; submersed leaves pec­tinate, ovate to obovate in outline, (6–) 12–29 (–65) × (12–) 14–18 (–50) mm, segments (10–) 12–20 (–28), linear-filiform, longest segment (7–) 9–25 (–29) mm; emersed leaves pectinate to pinnatifid proximally, lanceolate to ovate or elliptic distally, 3–14 (–31) × 1–5 (–7) mm, margins serrate to lobed. Inflorescences to 60 cm; flowers proximally pistillate, medially bisexual, distally staminate; bract­eoles cream, ovate to triangular or deltate, 0.6–1.1 ×0.3–0.9 mm, margins serrate to irregularly lobed. Staminate flowers: sepals cream, lanceolate to nar­rowly triangular, 0.5–0.8 (–0.9) × 0.1–0.2 mm; petals per­sistent, cream, elliptic to obovate, 1.4–3 × 0.7–1.3 mm; stamens 4, filaments to 1.6 mm, anthers 1.3–2.2 × 0.3–0.7 mm. Pistillate flowers: sepals cream, triangular, (0.1–) 0.2–0.6 × 0.1–0.3 (–0.4) mm; petals caducous, cream, elliptic to obovate, 1.5–2 (–3) × 0.8–1 mm; pistils 0.8–1.7 mm, stigmas red to ± purple, to 0.4 mm. Fruits ovoid to subglobose, deeply 4-lobed. Mericarps tan to redbrown, cylindric to narrowly ovoid, 1–1.5 ×0.5–0.8 mm, transversely orbiculate to widely elliptic, abaxial surface bluntly 4-angled, rounded to slightly flattened, densely papillate, with 4 shallow, longitudinal ridges, ridges sometimes with inconspicuous, shallow wings proximally, ribs absent.


Phenology: Flowering and fruiting May–Oct.
Habitat: Oligotrophic to eutrophic waters, lakes, ponds.
Elevation: 0–600 m.

Distribution

B.C., N.B., Ont., P.E.I., Que., Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., Wash., W.Va., Wis.

Discussion

In flower, Myriophyllum heterophyllum is one of the more distinctive water-milfoils; it has relatively large, wide, ovate bracts and elongate spikes, on which leaves transition from pectinate to entire and often trail along the water surface. Plants are often very robust and bushy, with thickened red stems and highly crowded leaf whorls.

D. H. Les and L. J. Mehrhoff (1999) suggested that Myriophyllum heterophyllum is invasive in New England and progressively spread northward from a more southern native range. It is known to be introduced in British Columbia. R. A. Thum et al. (2011) provided genetic evidence that invasive populations of M. heterophyllum from New England, the Pacific Northwest, and California represent multiple introductions from the native Atlantic coastal plain and interior continental range.

S. G. Aiken (1981) suggested that Myriophyllum heterophyllum produces turions; we have seen no evidence of this, and it is likely that new shoots produced along rhizomes late in the growing season have been mistaken for turions.

Selected References

None.

Lower Taxa

None.
rounded +  and slightly flattened +
0.13 cm1.3 mm <br />0.0013 m <br /> (0.22 cm2.2 mm <br />0.0022 m <br />) +
0.03 cm0.3 mm <br />3.0e-4 m <br /> (0.07 cm0.7 mm <br />7.0e-4 m <br />) +
aristate +  and fringed +
Robin W. Scribailo +  and Mitchell S. Alix +
Michaux +
pectinate +, pinnatifid +, lobed +  and unlobed +
0.06 cm0.6 mm <br />6.0e-4 m <br /> (0.11 cm1.1 mm <br />0.0011 m <br />) +
ovate +  and triangular or deltate +
0.03 cm0.3 mm <br />3.0e-4 m <br /> (0.09 cm0.9 mm <br />9.0e-4 m <br />) +
opposite +, alternate +  and paired +
Two-leaf or various-leaved water-milfoil +  and myriophylle à feuilles variées +
B.C. +, N.B. +, Ont. +, P.E.I. +, Que. +, Ala. +, Ark. +, Conn. +, Del. +, D.C. +, Fla. +, Ga. +, Ill. +, Ind. +, Iowa +, Kans. +, Ky. +, La. +, Maine +, Md. +, Mass. +, Mich. +, Minn. +, Miss. +, Mo. +, N.H. +, N.J. +, N.Y. +, N.C. +, Ohio +, Okla. +, Pa. +, R.I. +, S.C. +, Tenn. +, Tex. +, Vt. +, Va. +, Wash. +, W.Va. +  and Wis. +
0–600 m. +
cylindric +
papillate +, tuberculate +, rugose +  and scabrous +
0 cm0 mm <br />0 m <br /> (0.16 cm1.6 mm <br />0.0016 m <br />) +
petiolate +  and sessile +
pistillate +  and staminate +
purple +, redbrown +, brown +, green +, olive-brown +, tan +  and light green +
indehiscent +
4-lobed +, ovoid +  and subglobose +
red punctate +
Oligotrophic to eutrophic waters, lakes, ponds. +
multiseriate +  and uniseriate +
perennial +
aquatic +  and semiaquatic +
indeterminate +  and determinate +
lateral +  and terminal +
0 cm0 mm <br />0 m <br /> (60 cm600 mm <br />0.6 m <br />) +
80+-flowered +  and simple +
heteromorphic +
subverticillate +
1.4 cm14 mm <br />0.014 m <br /> (3.1 cm31 mm <br />0.031 m <br />) +
0.5 cm5 mm <br />0.005 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
0.3 cm3 mm <br />0.003 m <br /> (1.4 cm14 mm <br />0.014 m <br />) +
emersed +  and submersed +
pectinate +  and pinnatifid proximally +
0.1 cm1 mm <br />0.001 m <br /> (0.5 cm5 mm <br />0.005 m <br />) +
2.5 cm25 mm <br />0.025 m <br /> (2.9 cm29 mm <br />0.029 m <br />) +
0.9 cm9 mm <br />0.009 m <br /> (2.5 cm25 mm <br />0.025 m <br />) +
serrate +  and entire +
serrate +  and irregularly lobed +
tan +  and redbrown +
0.1 cm1 mm <br />0.001 m <br /> (0.15 cm1.5 mm <br />0.0015 m <br />) +
transversely orbiculate +  and widely elliptic +
0.05 cm0.5 mm <br />5.0e-4 m <br /> (0.08 cm0.8 mm <br />8.0e-4 m <br />) +
triangular +
indehiscent +
2.9 cm29 mm <br />0.029 m <br /> (6.5 cm65 mm <br />0.065 m <br />) +
1.8 cm18 mm <br />0.018 m <br /> (5 cm50 mm <br />0.05 m <br />) +
1.2 cm12 mm <br />0.012 m <br /> (2.9 cm29 mm <br />0.029 m <br />) +
1.4 cm14 mm <br />0.014 m <br /> (1.8 cm18 mm <br />0.018 m <br />) +
crassinucellate +  and bitegmic +
pistillate +  and staminate +
0.2 cm2 mm <br />0.002 m <br /> (0.3 cm3 mm <br />0.003 m <br />) +
1.5mm;2mm +
rudimentary +
elliptic +  and obovate +
0.08 cm0.8 mm <br />8.0e-4 m <br /> (0.1 cm1 mm <br />0.001 m <br />) +
0 cm0 mm <br />0 m <br /> (0.5 cm5 mm <br />0.005 m <br />) +
Flowering and fruiting May–Oct. +
4-carpellate +  and 3-carpellate +
0.08 cm0.8 mm <br />8.0e-4 m <br /> (0.17 cm1.7 mm <br />0.0017 m <br />) +
Fl. Bor.-Amer. +
shallow +
purple +, redbrown +, brown +, green +, olive-brown +, tan +  and light green +
less ovoid +  and oblong or more or less globose cruciate +
linear-filiform +
0.01 cm0.1 mm <br />1.0e-4 m <br /> (0.02 cm0.2 mm <br />2.0e-4 m <br />) +
0.03 cm0.3 mm <br />3.0e-4 m <br /> (0.04 cm0.4 mm <br />4.0e-4 m <br />) +
persistent +
rudimentary +
triangular +  and lanceolate +
0.01 cm0.1 mm <br />1.0e-4 m <br /> (0.03 cm0.3 mm <br />3.0e-4 m <br />) +
brown splotches +  and red +
prostrate +  and decumbent +
0 cm0 mm <br />0 m <br /> (250 cm2,500 mm <br />2.5 m <br />) +
red +  and more or less purple +
fimbriate +  and clavate +
0 cm0 mm <br />0 m <br /> (0.04 cm0.4 mm <br />4.0e-4 m <br />) +
petiolate +  and sessile +
smooth +  and more or less papillate +
Myriophyllum heterophyllum +
Myriophyllum +
species +
terminal +  and lateral +
shallow +
inconspicuous +
transitional +
intermediate +