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Montana Field Guides

Whorled Water-milfoil - Myriophyllum verticillatum

Status Under Review
Native Species

Global Rank: G5
State Rank: SU
(see State Rank Reason below)

Agency Status
USFWS:
USFS:
BLM:
MNPS Threat Rank:
C-value: 4

External Links






State Rank Reason (see State Rank above)
Myriophyllum verticillatum has mostly been collected in the northwest, but is represented in the southwest, Rocky Mountain Front, and eastern Montana with herbarium specimens. Although aquatic plants are generally under-represented in our floras, aspects of its habitat or threats to its population are not suggesting rarity at this time. 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 verticillatum in Montana.
 
General Description
PLANTS: Aquatic, perennials with finely dissected, whorled submerged leaves, and emerged leaves occurring within the inflorescence. Stems may branch. Wintering buds (turions) are absent. Source: Giblin et al. [eds.] 2018.

LEAVES: Submerged leaves are well-developed (up to 45 mm long) and mostly in whorls of 4 with (9-) 18-34 leaf segments. Emerged leaves are well-developed (larger than the flowers or fruits), whorled, and pinnately divided or lobed (more than half-way to mid-vein) within the inflorescence. 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.

Diagnostic Characteristics
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.

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.
* Turions absent.

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.
* 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
Present
 


Range Comments
Alaska to California and east to the Atlantic coast (Giblin et al. [eds.] 2018).

Observations in Montana Natural Heritage Program Database
Number of Observations: 24

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

Recency

 

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



Habitat
Shallow to rather deep water of ponds and lakes in the plains, valleys, and montane zones of Montana (Lesica et al. 2012).

Reproductive Characteristics
FLOWERS
On the same plant male and female flowers are usually 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. Male flowers have yellowish petals and 8 stamens. Source: Giblin et al. [eds.] 2018.

FRUITS
Fruits are drupe-like or nut-like with 4 carpels. Fruit segments are roundish to nearly round with shallow, longitudinal ridges and no wings or cross-ribs. Faces are smooth. Fruit segments are 2-3 mm long. Source: Lesica et al. 2012; Giblin et al. [eds.] 2018.

Plants develop turions that are brown to red-brown, oblanceolate-shaped, and 1-5 cm long.

References
  • Literature Cited AboveLegend:   View Online Publication
    • Giblen, David E., Ben S. Legler, Peter F. Zika, and Richard G. Olmstead (eds). 2018. Flora of the Pacific Northwest: An Illustrated Manual. Second Edition. University of Washington Press in Association with Burke Museum of Natural History an dCulture, 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.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Aiken, S.G. 1981. A Conspectus of Myriophyllum (Haloragaceae) in North America. Brittonia 33 (1): 57-69. A81AIK01PAUS.
    • Britton, N. L. and A. B. Brown. 1913. An Illustrated Flora of the Northern United States, Canada, and the British Possessions. 2nd Edition in 3 Volumes. New York, NY: Charles Scribner's Sons. B13BRI01PAUS.
    • Fassett, Norman C. 1940. A Manual of Aquatic Plants, 1st ed. New York: McGraw-Hill. B57FAS01PAUS.
    • Fernald, M. L. 1950. Gray's manual of botany. Eighth edition. A handbook of the flowering plants and ferns of the central and northeastern United States and Adjacent Canada. American Book Co., New York.
    • Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. New York Botanical Garden, Bronx, NY. 910 pp.
    • Linnaeus, C. 1753. Species Plantarum. A fascimile of the first edition printed by Adlard & Son, Bartholomew Press, Dorking, Great Britain. 2 vol.
    • Weishaupt, C.G. 1971. Vascular Plants of Ohio, Third Ed. Kendall/Hunt Publishing Co. Dubuque, Iowa. B71WEI01PAUS
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Citation for data on this website:
Whorled Water-milfoil — Myriophyllum verticillatum.  Montana Field Guide.  .  Retrieved on , from