Myriophyllum quitense
Myriophyllum laxum
Andean water-milfoil, waterwort milfoil, waterwort water-milfoil
loose watermilfoil, Piedmont water-milfoil
often branched, to 3 m. Turions absent.
sometimes branched, to 1 m. Turions absent.
mostly in whorls of (3 or)4(or 5), sometimes opposite to subopposite, heteromorphic;
petiole 0–4 mm; submersed leaves pectinate to lobed (basalmost leaves opposite to subopposite, reduced, margins entire), ovate to obovate in outline, (3–)5–25(–35) × (2–)3–18(–20) mm, segments (2 or)3–9(–11), linear, ± applanate, longest segment (7–)8–15(–17) mm; emersed leaves pinnatisect to lobed or entire, ovate to oblong in outline, 2–9 × 1–6 mm, margins dentate to minutely serrate.
usually alternate and/or in whorls of 3(or 4), sometimes opposite or irregular, heteromorphic;
petiole 0–3 mm; submersed leaves pectinate, elliptic to obovate in outline, 9–27(–31) × 6–18(–22) mm, segments (6–)8–12(–16), linear-filiform, longest segment (4–)8–17(–21) mm, surfaces with numerous black, ascidiate trichomes; emersed leaves pectinate to pinnatifid proximally, elliptic to obovate, spatulate, or oblanceolate, (0.6–)0.7–2.3(–2.7) × (0.1–)0.2–0.7(–1) mm, with black, ascidiate trichomes scattered on surfaces and in axils.
to 8 cm;
flowers proximally pistillate, medially bisexual, distally staminate;
bracteoles cream, deltate, 0.5–1 × 0.2–0.6 mm, margins dentate to serrate, with glandular tip.
to 27 cm;
flowers proximally pistillate, medially bisexual, distally staminate;
bracteoles cream, lanceolate to triangular, 0.3–0.8 × 0.1–0.2(–0.3) mm, margins irregularly lobed, apex often narrowly apiculate.
sepals green to cream, ovate to deltate, (0.2–)0.3–0.5(–0.7) × (0.1–)0.2–0.4(–0.5) mm;
petals persistent, ± purple, oblong, 2–3 × 0.5–1.5 mm;
stamens 8, filaments to 0.6 mm, anthers 1.8–2.5 × 0.2–0.6 mm.
sepals cream, lanceolate to narrowly triangular, 0.1–0.3 ×0.1–0.2 mm;
petals persistent, cream, suffused with ± red at tips, obovate to oblanceolate, 1.5–1.9 ×0.6–1.1 mm;
stamens 4, filaments to 1.3 mm, anthers 1.2–1.5(–1.7) × 0.2–0.4(–0.6) mm.
sepals cream, deltate, 0.2–0.5 × 0.1–0.4 mm;
petals ± persistent, cream, ± cucullate, elliptic, 0.1–0.5 × 0.2–0.3 mm;
pistils 1.1–2.2 mm, stigmas cream to ± purple, to 0.6 mm.
sepals cream, lanceolate to ovate, 0.1–0.3 × 0.1–0.2 mm;
petals caducous, cream, elliptic to obovate, 0.4–0.5 × 0.1–0.3 mm;
pistils (0.5–)0.7–1.1(–1.3) mm, stigmas red to ± purple, to 0.5 mm.
cylindric to oblong, 4-lobed.
narrowly globose, 4-lobed.
tan to olive-brown, cylindric to ovoid, 1.5–1.8 × 0.6–0.8 mm, transversely elliptic, abaxial surface rounded, smooth, sometimes with a shallow, longitudinal ridge, wings and ribs absent.
brown to purple, cylindric to narrowly ovoid, 1–1.4 × (0.4–)0.6–0.8(–1.1) mm, transversely elliptic, abaxial surface rounded to shallowly 2-angled, densely tuberculate proximal to midpoint, tubercles crowded, relatively large, rarely with 2 shallow, partial longitudinal wings, tubercles often obscuring wings, ribs absent.
= 42.
Myriophyllum quitense
Myriophyllum laxum
The most distinguishing feature of Myriophyllum quitense is the production of relatively large, ovate distal floral bracts with serrate margins. This characteristic is shared only with M. heterophyllum; however, M. quitense has eight stamens and the latter has four.
The proximal submersed leaves of most Myriophyllum species are uniformly pectinate, but those of M. quitense can range from entire or lobed to pectinate. This species often exhibits a pronounced transition from three or four proximal nodes of large, opposite, spatulate or lobed prophylls, to nodes of besomiform whorled leaves having obtriangular laminar surfaces and distal pinnatifid segments resembling those of pectinate leaves. In addition, the unusual grayish blue color of the foliage and whitish rhizomes are useful characteristics for distinguishing submersed vegetative specimens of M. quitense from similar species, such as M. sibiricum.
Myriophyllum quitense has a highly disjunct distribution in North America and South America (A. E. Orchard 1981; O. Ceska et al. 1986). S. G. Aiken (1981) and R. Couch and E. Nelson (1988) suggested that M. quitense was introduced into North America by migratory waterfowl. Both Ceska et al. and M. L. Moody and D. H. Les (2010) regarded it as native to North America. It has been reported from New Brunswick and Prince Edward Island (D. F. McAlpine et al. 2007) and further range extensions would seem likely given the level of disjunction in distribution.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Myriophyllum laxum is a coastal plain species that has a very restricted range in the southeastern United States. It is most similar vegetatively to M. humile, with which it shares a delicate habit. The two have historically been reported to overlap in range in Virginia; no specimens of the former have been seen from that state. In M. laxum the submersed leaves are usually whorled but often irregular and sometimes alternate; in M. humile the leaves are usually opposite or alternate and almost never whorled. The proximal half of mericarps of M. laxum is densely covered with large, mounded tubercles; mericarps of M. humile tend to be uniformly, sparsely to densely covered with smaller tubercles and have distinct tuberculate ridges typically running the entire length of the mericarp. The floral bracts are also very different in the two species and the flowers are much smaller in M. laxum.
Myriophyllum laxum has sometimes been confused with M. heterophyllum; however, they can be distinguished by the number of submersed leaf segments with M. laxum typically having 8–12 versus 12–20 for M. heterophyllum. They can also be easily distinguished by differences in floral and fruit characters. Myriophyllum laxum also interbreeds with M. heterophyllum (M. L. Moody and D. H. Les 2010; R. A. Thum et al. 2011), producing a hybrid that is often fertile, having floral and fruit characters very similar to those observed in M. laxum, but having highly variable leaf morphology typical of both parental species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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