Montana Field Guide

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.

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.

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

FLOWERS
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
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.

STATE THREAT SCORE REASON
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).