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Andean Water-milfoil - Myriophyllum quitense

Species of Concern
Native Species

Global Rank: G4?
State Rank: S3
(see State Rank Reason below)

Agency Status
MNPS Threat Rank:
C-value: 4

External Links

State Rank Reason (see State Rank above)
Myriophyllum quitense is an aquatic plant that has recently (2008-2016) been found in three waterbodies of Montana. Plants are found in slow-moving rivers that vary in water quality from the Madison River in Yellowstone National Park to Toston Reservoir on the Missouri River. These locations represent a very narrow geographical portion of Montana. Proper identification of Myriophyllum species require careful collections to obtain flowering or fruiting structures, use of an appropriate and current taxonomic key, and time spent studying the specimen. More surveys are greatly needed to assess the true abundance and distribution of Myriophyllum quitense in Montana.
  • Details on Status Ranking and Review
    Andean Water-milfoil (Myriophyllum quitense) Conservation Status Review
    Review Date = 06/17/2019
    View State Conservation Rank Criteria
    Range Extent

    ScoreD - 1,000-5,000 sq km (~400-2,000 sq mi)

    Comment3,350 square kilometers

    Area of Occupancy

    ScoreC - 3-5 4-km2 grid cells

    CommentPlant occurs in 5 of the 30,590 4x4 square-kilometer grid cells that cover Montana.

    Number of Populations

    ScoreB - 6 - 20

    Comment7 observations found in three water bodies

    Number of Occurrences or Percent Area with Good Viability / Ecological Integrity

    ScoreB - Very few (1-3) occurrences with excellent or good viability or ecological integrity

    CommentAssumption based on descriptive words of 'common' or 'extensive population'.


    ScoreD - Low

    CommentProtections for water quality occur on the Madison within YNP. Toston Reservoir does not have pristine water.

General Description
PLANTS: Aquatic, perennials with finely dissected, whorled submerged leaves and emerged leaves that only occur within the inflorescence. Stems are simple or branched. Wintering buds (turions) are absent. Source: Giblin et al. [eds.] 2018.

LEAVES: Submerged leaves are well-developed, in whorls of 4-5 with 6-12 leaf segments. Emerged leaves are well-developed (larger than the flowers or fruits), whorled, and occur within the inflorescence. Emerged leaves are ovate and serrate in the upper half of the inflorescence. Emerged leaves dry to become dark gray. At the base of branches or shoots are strap-shaped, entire to pectinate (toothed like a comb), somewhat opposite, and very reduced leaves. Source: Giblin et al. [eds.] 2018.

INFLORESCENCE: An emergent, terminal spike. The spike consists of separate male and female flowers and emerged leaves that are greater than the flowers and fruits. Source: Giblin et al. [eds.] 2018. See Reproductive Characteristics for distinguishing characteristics.

Diagnostic Characteristics
Andean Water-milfoil - Myriophyllum quitense, native and desirable:
* All emergent leaves are medium to dark green, smooth, longer than the flowers and fruits, and dry to dark grey.
* Emergent leaves on the upper half of inflorescence are ovate and serrate.
* At the base of branches or shoots are strap-shaped, entire to pectinate (toothed like a comb), somewhat opposite, and very reduced leaves.
* Flowers have 8 stamens.
* Submerged leaves are in whorls of 4-5 with 6-12 segments.
* Plants remain stiff when removed from water.
* Turions absent.

Whorled Water-milfoil - Myriophyllum verticillatum, native and desirable:
* Emergent leaves are longer than the flowers and fruits and pinnately divided or lobed more than half-way to mid-vein.
* Flowers have 8 stamens.
* Submerged leaves are generally in whorls of 4, often with 12-22 segments.
* Fruit segments are round(-ish) with shallow, longitudinal ridges and no wings or cross-ribs.
* Turions present (balls of small leaves that develop from tips of vigorous vegetative shoots): brown to red-brown and 1-5 cm long.

Common Water-milfoil - Myriophyllum sibiricum, native, desirable:
* Combination of flowering spikes with emergent leaves less than 4 mm and whorled submerged leaves with 4 to 16 pairs of segments that mostly spread or are perpendicular to the apex.
* Submerged leaves are often in whorls of 4 with 6-16(-24) segments. Segments spread or lay perpendicular to the rachis at base, but may ascend towards the apex.
* Lower pair of segments are longest and gradually shorten towards the leaf tip.
* Plants remain stiff when removed from water.
* Turions present: dark green, broadly cylindrical, composed of reduced and thickened leaves, and may remain persistent on next year’s new growth.

Eurasian Water-milfoil - Myriophyllum spicatum, exotic, noxious, invasive:
* Combination of flowering spikes with emergent leaves less than 4 mm and whorled submerged leaves with 14 to 24 pairs of segments that ascend.
* Submerged leaves have linear segments that are mostly equal in length.
* Vegetative shoot tips are often dense.
* Plants readily collapse when removed from water.
* Turions (cylinders or balls of small leaves) are absent.

Species Range

Range Comments
Plants are found from British Columbia, Canada southward to both sides of the Oregon and Washington Cascade Range, and eastward to Idaho, Montana, and Utah. Plants occur in Mexico and South America. Source: Giblin et al. [eds.] 2018.

Observations in Montana Natural Heritage Program Database
Number of Observations: 7

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Slow rivers and streams or large lakes in the valleys and montane zones of Montana (Lesica et al. 2012; Giblin et al. [eds.] 2018).

Reproductive Characteristics
On the same plant male and female flowers are separate, generally one per axil, and usually subtended by 2 or more tiny bracteoles. In general male flowers grow above the female flowers in the terminal spike-like inflorescence. Sepals are white. Petals are 2-3 mm long and quickly deciduous. Male flowers have 8 stamens. Source: Lesica et al. 2012; Giblin et al. [eds.] 2018.

Fruits are drupe-like or nut-like with 4 carpels. Fruit segments are about 2 mm long. Source: Giblin et al. [eds.] 2018.

Plants do not develop turions.

  • Literature Cited AboveLegend:   View Online Publication
    • Giblin, David E., Ben S. Legler, Peter F. Zika, and Richard G. Olmstead (editors). 2018. Flora of the Pacific Northwest: An Illustrated Manual. Second Edition. University of Washington Press in Association with Burke Museum of Natural History and Culture, Seattle, Washington. 882 pp.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
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Citation for data on this website:
Andean Water-milfoil — Myriophyllum quitense.  Montana Field Guide.  .  Retrieved on , from