Myriophyllum spicatum
Myriophyllum heterophyllum
Eurasian water-milfoil, myriophylle en épi, spike water milfoil, water milfoil
broadleaf water-milfoil, changeleaf parrotfeather, myriophylle à feuilles variées, two-leaf milfoil, two-leaf water-milfoil, vari-leaf water-milfoil, variable-leaf water-milfoil, varied-leaf watermilfoil, various-leaf water-milfoil
often much-branched distally, to 6 m. Turions absent.
often branched, to 2.5 m. Turions absent.
in whorls of (3 or)4(or 5), heteromorphic;
petiole 0–0.4 mm; submersed leaves pectinate, obovate in outline, (14–)18–32(–36) × 10–20(–30) mm, segments (20–)24–36(–42), linear-filiform, longest segment 2–20(–26) mm, usually parallel and all in 1 plane, forming angles less than 45° with central axis; emersed leaves pectinate to pinnatifid proximally, with abrupt transition to obovate or elliptic, sometimes distally spatulate, in outline, margins of distal leaves entire to serrate to shallowly lobed, 1–2.3 × 0.6–1(–1.5) mm.
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.
to 15 cm;
flowers proximally pistillate, medially bisexual, distally staminate;
bracteoles cream to stramineous to purple, with distinct reddish or brown margins, usually ovate to depressed-ovate or obovate, sometimes elliptic to triangular or rhombic, 0.5–0.9 × 0.4–0.7 mm, margins entire or serrate, sometimes with distal, irregular, membranous fringe.
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.
sepals cream to stramineous, triangular, 0.3–0.4 × 0.2–0.3 mm;
petals caducous, cream to red or dark purple, oblong to elliptic or obovate, 1.5–2.5(–3) × 0.8–1 mm;
stamens 8, filaments to 1.2 mm, anthers greenish cream to yellow or purple, 1–2.2 × 0.4–0.8 mm.
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.
sepals cream to green to purple, lanceolate to deltate or ovate, 0.1–0.3 × 0.1–0.2 mm;
petals often persistent, cream, widely ovate, 0.6–0.8 × 0.3–0.4 mm;
pistils 0.9–1.2 mm, stigmas white to red to ± purple, 0.2–0.7 mm.
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.
globose, 4-lobed.
ovoid to subglobose, deeply 4-lobed.
olive-green to brown, cylindric to narrowly ovoid, 1.5–2.2 × 0.8–1.3 mm, transversely widely obovate, abaxial surface broadly rounded, sparsely and irregularly tuberculate, margins smooth to tuberculate, sometimes with 2 shallow, longitudinal ridges, wings and ribs absent.
tan to red-brown, 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.
= 42.
Myriophyllum spicatum
Myriophyllum heterophyllum
Myriophyllum spicatum is considered one of the worst nuisance aquatic weeds in North America. Identification of this species is critical for management of lakes. Until the early 1900s, the widely accepted view was that M. spicatum was native to North America and was conspecific with European M. spicatum. M. L. Fernald (1919c) described M. exalbescens to distinguish all North American specimens from European M. spicatum, with the former name subsequently being changed to M. sibiricum due to nomenclatural precedence (S. G. Aiken and A. Cronquist 1988). The first to recognize the presence of both species in North America was apparently C. F. Reed (1970b). E. Hultén (1941–1950), B. C. Patten (1954), and S. A. Nichols (1975) proposed alternatively that M. spicatum and the native M. sibiricum form a continuum of variation, suggesting the two taxa may simply represent varieties or subspecies of a highly variable cosmopolitan species. Based on a study of herbarium collections, R. Couch and E. Nelson (1985, 1992) believed that M. spicatum was introduced from Europe in the 1940s and subsequently spread throughout the United States and Canada. A recent biogeographic study of cpDNA haplotypes indicates this species was introduced to North America from China and Korea (M. L. Moody et al. 2016).
Based upon examination of specimens for this treatment, and as pointed out by A. E. Orchard (1981), most of the characters initially proposed by M. L. Fernald (1919c) and expanded upon by S. G. Aiken (1981) that are thought to be reliable for distinguishing the two species, such as size and shape of floral bracts and bracteoles, anther length, swollen base of inflorescence, color of the stem in dried material, extent of branching, and differences in mericarps, break down when a wide range of North American herbarium material is examined. One of the few useful vegetative characters to distinguish these species in the northern regions of North America is that M. sibiricum often produces turions in the latter part of the growing season, whereas M. spicatum does not (E. Hultén 1947). The most commonly used vegetative character to distinguish the two species is the number of leaf segments in submersed leaves (Fernald). When attempting to distinguish plants of the latter two species, this is a reliable character, but only when specimens have low (6–18) or high (24–42) segment numbers; plants often have submersed leaves with intermediate segment numbers.
Molecular studies have shown that the overlap seen in morphological characters, such as leaf segment number, between Myriophyllum sibiricum and M. spicatum may be the result of frequent and widespread hybridization (M. L. Moody and D. H. Les 2002, 2007b; A. P. Sturtevant et al. 2009). Hybrids between these two species can have leaf segment numbers from 16–28 (Moody and Les 2007b), which overlaps with leaf segment numbers for both M. sibiricum (6–18) and M. spicatum (24–36). A reliable method to distinguish these taxa when there is overlap in this character state is DNA fingerprinting (Moody and Les 2002).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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- Local Web sites: Flora NW, Go Botany, IL Wildflowers, KS Wildflowers, LA Plants, MD Biodiversity, MI Flora, MN Wildflowers, MO Plants, PNW Herbaria
- WildflowerSearch
- iNaturalist (observations)
- USDA Plants Database
- LBJ Wildflower Center
- SEINet
- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
