Myriophyllum spicatum
Myriophyllum aquaticum
Eurasian water-milfoil, myriophylle en épi, spike water milfoil, water milfoil
Brazilian water-milfoil, parrot feather, parrot feather watermilfoil, parrot's feather, parrot's-feather water-milfoil, parrot- or water-feather, South American water milfoil, water feather
often much-branched distally, to 6 m. Turions absent.
branched or unbranched, to 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.
in whorls of 4–6(–8), homomorphic;
petiole to 9.6 mm; submersed leaves pectinate, oblanceolate to obovate in outline, (20–)25–70(–75) × (4–)5–26(–32) mm, segments (14–)16–36(–40), filiform, longest segment (2–)4–27(–33) mm; emersed leaves becoming unmodified floral bracts.
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 20 cm;
flowers unisexual;
bracteoles cream to stramineous, (0.3–)0.5–1(–1.5) × 0.1–0.3(–0.5) mm, margins subulate to 3-fid.
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, ovate to deltate, 0.7–0.8 ×0.3 mm;
petals yellow, weakly cucullate, (2.3–)2.7–3.1 × 0.8–1.1 mm;
stamens 8, filaments to 1.2 mm, anthers yellow, linear-oblong, (1.8–)2–2.7 × 0.2 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, lanceolate to deltate, 0.3–0.5 × 0.1–0.2(–0.4) mm;
petals rudimentary or absent;
pistils to 0.8 mm, stigmas white, to 0.3 mm.
globose, 4-lobed.
cylindric to ovoid, shallowly 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.
olive-green to brown, cylindric, 1.7 × 0.6–0.7 mm, narrowly obovate, abaxial surface rounded, ridges, wings and ribs absent.
= 42.
Myriophyllum spicatum
Myriophyllum aquaticum
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 the flora area, Myriophyllum aquaticum is an introduced invasive aquatic species, existing as pistillate populations throughout North America (R. Couch and E. Nelson 1992); it is native to the lowlands of South America (A. E. Orchard 1981). It has an unusual habit among North American species of Myriophyllum, where it is often observed as a robust emergent aquatic along shorelines. It can be found also growing to a depth of 5 m in lakes, with the largest submersed leaves recorded for any North American species of Myriophyllum. The leaves of M. aquaticum are very distinctive, being largely oblanceolate and two to three times as long as broad, with a large number of uniform, short-pinnate segments, often arranged in whorls of six or more.
Myriophyllum aquaticum has been reported from Iowa and Montana; no specimens have been seen that confirm these reports.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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- Local floras: BC, CA, OR, WA
- Local Web sites: CalFlora, CalPhotos, Flora NW, Go Botany, IL Wildflowers, KS Wildflowers, LA Plants, MD Biodiversity, 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
