Missoula County Weed District & Extension

***Photographs of diagnostic features coming soon!!!***

aquatic key title
Adapted from Hitchcock, Dorn and Lackschewitz
1a. Stems Lacking; entire plant floating and smaller (usually much smaller than 2 cm in diameter) Lemnaceae 
1b. Plants larger and usually with obvious stems  2
2a. Leaves large (>10 cm) and round to broadly elliptic in outline, borne on the ends of long petioles and floating flat on the surface of the water (water lilies) Nymphaeaceae
2b. Leaves smaller, narrower or not always floating
3a. Plants withouth leafy stems; all leaves grass-like and attached at base 4
3b. Plants with leafy stems; leaf shape various 8
4a. Leaves with a sac of white spores at the base Isoetaceae
4b. Leaves without spore-sac at base 5
5a. Leaves with a well-differentiated blade, broader than the long petiole Scrophulariaceae
5b. Leaves grass-like,  without a well differentiated blade 6
6a. Leaves needle-like and round in cross section Cyperaceae
6b. Leaves not as above 7
7a. Leaves triangular in cross section with twisted ends Butomaceae
7b. Leaves flattened, not needle-like or triangular in cross section Alismataceae, Sarganiaceae (vegetative Forms)
8a. Underwater leaves highly dissected into hair-like segments 9
8b. Underwater leaves linear to elliptic, but not dissected 12
9a. Leaves with small, egg-shaped bladders among the leaflets Lentibulariaceae
9b. Leaves without bladders 10
10a. Leaves 1 per node; flowers conspicuous with yellow or white petals Ranunculaceae
10b. Leaves whorled (>2 per node); flowers inconspicuous, without petals 1
11a. Ultimate leaflets with toothed margins; stems usually green Ceratophyllaceae
11b. Margins of ultimate leaflets smooth; stems often reddish Haloragaceae
12a. Leaves whorled (>2 per node) 13
12b. Leaves opposite or alternate 15
13a. Leaves scarcely 1mm wide Najadaceae
13b. Leaves greater than 1.5mm wide 14
14a. Leaves <2mm x 10-35mm long with smooth edges, 6 or more per node Hippuridaceae
14b. Leaves with 6 or less per node, or if more than 6, have saw-toothed margins and sharp teeth on mid-vein of leaf's lower surface Hydrocharitaceae 
15a. Submersed leaves opposite (2 per node) 16
15b. Submersed leaves alternate (1 per node) 17
16a. Leaves at least 2cm long Zannichelliaceae
16b. Leaves < 2cm long Callitrichaceae
17a. Leaves long and tape-like on short stems Hydrocharitaceae
17b. Leaves not as above 8
18a. Submersed leaves narrowly elliptic to nearly round in outline (mostly <5 times as long as wide) 19
18b. Submersed leaves linear and grasslike (mostly >10 times as long as wide) 21 
19a. Leaves with 4 leaflets, resembling a 4-leaf clover Marsileaceae
19b. Leaves not divided into 4 leaflets 20
20a. Leaf veins parallel to each other or nearly so Potamogetonaceae
20b. Leaf veins branching off of the midrib Polygonaceae
21a. Base of the leaf expanded into a pale, membranous appendage (stipule) that surrounds the stem Potamogetonaceae
21b. Base of the leaf without stipules 22
22a. Leaves on or near the surface shaped like an arrowhead Alismataceae
22b. Surface leaves linear or grasslike 23
23a. Base of the leaves Y-shaped in cross-section; flowers and fruits borne in round clusters Sarganiaceae
23b. Leaves nearly flat at the base with a pale, membranous appendage on the inner surface (ligule) where it joins the stem; flowers and fruits not borne in round clusters Gramineae
1a. Individual leaves (thalli) up to 1mm long, without roots Wolffia punctata
1b. Individual leaves (thalli) >2mm, at least some roots 2 
2a. Plants with >1 root per leaf Spirodella polyrhiza
2b. Plants with 1 root per leaf 3
3a. Leaves 2-4mm long, broadly elliptic to nearly round, separate or few together Lemna minor
3b. Leaves 6-12mm long, oar-shaped, often several attached together Lemna trisulca
1a. Three (four) purplish sepals and petals; petioles attached to leaf center (leaves rounded) Brasenia shreberi 
1b. Sepals and petals at least 4, greenish, yellow or white; leaves with heart-shaped bases 2
2a. Sepals 4, about as large as the petals but less showy; petal white or pinkish Nymphaea ordorata
2b. Sepals greater than 4; petals not as above 3
3a. Sepals usually number 6, 2.5-3.5 cm long; stamens yellow Nuphar variegata
3b. Sepals generally 9, 3.5-6 cm long; stamens mostly reddish to purplish Nuphar polysepala
1a. Translucent margin of sporophylls extending more than 2cm above the megasporangium Isoetes howellii 
1b. Translucent margin of sporophylls extending less than 2cm 2
2a. Surface of megaspores with spines, plants usually in montana or lower subalpine zone Isoetes echinospora
2b. Surface of megaspores with bumps or short ridges, plants common in upper subalpine and timeberline Isoetes bolanderi
1 Limosella  aquatica
1a. Stigmas 3; achene 3-sided or rounded in cross-section 2
1b. Stigmas 2 (rarely 3); achene 2-sided (lens shaped) in cross section 4
2a. Tubercle cone-shaped, without a groove around the base separating it from the body of the achene Eleocharis pauciflora
2b. Tubercle more disc-shaped, with a basal groove 3
3a. Plants perrenial; anthers (dry) >.7mm long; flower scales >1.5mm long Eleocharis acicularis
3b. Plants annual; anthers <.5mm long; flower scales <1.5mm long Eleocharis bella
4a.  Tubercle constricted where it joins the body of the achene; common Eleocharis palustris 
4b. Tubercle flattened and not constricted at the base; uncommon Eleocharis ovata 
1 Invasive species listed as a Noxious Weed in the state of Montana. This email address is being protected from spambots. You need JavaScript enabled to view it. Butomus umbellatus
1a. Emergent or floating leaves with arrowhead-shaped blades (2 lobes at the base) Sagittaria cuneata
1b. Emergent or floating leaves with elliptical or lance shaped leaves 2 
2a.  Inflorescence surpassing the leaves, leaf blades mostly >3 cm wide  Alisma plantago-aquatica 
2b. Leaves surpassing the inflorescence, blades mostly <3 cm wide Alisma gramineum 
1a. Achene shaped like a cupcake, abruptly narrowed to the beak; inflorescence usually branched Sparganium eurycarpum
1b. Achene elliptic with a constricted middle, more peanut shaped; inflorescence usually unbranched Sparganium angustifolium
1a. Delicate plants with flowers 8 mm long, lower lip >2 times longer than spur; bladders few Utricularia minor
1b. Stouter plants with flowers > 14 mm long, lower lip <2 times spur, bladders many Utricularia vulgaris
1 Ranunculus aquatilis
1 Ceratophyllum demersum
HALORAGACEAE - under construction
1a. Leaves 1-3 cm, tapered at least from mid-length to a long slender point; seed coat smooth and shining Najas flexilis
1b. Leaves 1-2 cm, tapered mainly for distal 2.5-3 mm to rounded but ultimately, finely pointed tip; seed coat coarsely pitted and dull Najas guadalupensis
1 Hippuris vulgaris
1a.  Leaves alternate, long and tape-like on short stems Vallisneria americana 
1b. Leaves whorled on long stems 2 
2a. Whorled leaves have saw-toothed edges with sharp teeth on mid-vein of lower leaf surface. Invasive species listed as a Regulated Weed in the state of Montana. This email address is being protected from spambots. You need JavaScript enabled to view it. Hydrilla verticillata 
2b. Leaves not as above 3 
3a. Main leaves at least 2.5 cm long by 2-3 mm wide in whorls of mostly 6; petals 10 mm. Invasive species of concern in the state of Montana. This email address is being protected from spambots. You need JavaScript enabled to view it. Egeria densa 
3b. Main leaves less than 2.5 cm long in whorls of 2-3 per node 4 
4a. Leaves 1-4 mm wide with blunt tips Elodea canadensis
4b. Leaves less than 1.5 mm wide, tapered to a long, slender point Elodea nuttallii
1 Zannichellia palustris
1a. Fruit conspicuously winged around the entire margin  Callitriche stagnalis 
1b. Winged margins of fruit inconspicuous or absent 2
2a. Leaves linnear; flower bracts absent  Callitriche hermaphroditica 
2b. Upper leaves broader; flower bracts usually present 3 
3a. Fruit sections 1/5-1/3 longer than broad; fruits usually with slight, winged margin on top  Callitriche verna 
3b. Fruit sections about as long as broad; winged margin absent Callitriche heterophylla 
1 Marsilea vestita
1a.  Leaves all 5 mm wide or less, mostly linear, thread-like or ribbon-like with nearly parallel sides, all submersed  2 
1b.  Leaves, or some of them, over 5 mm wide, these often elliptic or ovate, and often floating 12 
2a. Leaves with 15 or more nerves  3 
2b. Leaves with 7 or fewer nerves 4 
3a. Leaves strictly 2 ranked, slightly auricled at base; leaf margins very finely toothed  Potamogeton robbinsii 
3b. Leaves not strictly 2 ranked, not auricled at base; leaf margins entire Potamogeton zosteriformis 
4a. Sheath of lower leaves inflated and much wider than the stem, green, 4 cm or more long  Potamogeton vaginatus 
4b. Sheath of lower leaves lacking or not as above 5 
5a. Leaves usually terete, or nearly so, thread-like, rarely flat, 1 nerved, somewhat septate with cross partitions  6 
5b. Leaves flat, ribbon-like, 3-7 nerved, usually not septate  7 
6a. Lower leaf sheaths 22 mm or less long, usually fused into a tube at the base; leaves with blunt tips  Potamogeton filiformis 
6b. Lower leaf sheaths 20 mm or more long, open to base; leaves usually with sharp, pointed tips Potamogeton pectinatus 
7a. Leaves finely serrulate, at least on upper half, 3-5 mm wide, resembling lasagna noodles. Invasive species listed as a Noxious Weed in the state of Montana.  This email address is being protected from spambots. You need JavaScript enabled to view it. Potamogeton crispus 
7b. Leaves entire, 1-3.5 mm wide  8 
8a. Leaf blades lacking glands at base; fruit with toothed or undulate keel down the back  Potamogeton foliosus 
8b. Leaf blades often with a pair of glands at the base, fruit usually not undulate-keeled  9 
9a. Stipules mostly membranous, greenish or sometimes whitish; leaves 3 nerved 10 
9b. Stipules fibrous, whitish; leaves 3-7 nerved 11 
10a. Achenes 1.5-2.5 mm long, 1.2-1.6 mm wide  Potamogeton pusillis 
10b. Achenes 2.5-3.5 mm long, 1.7-2.5 mm wide  Potamogeton obtusifolius 
11a. Leaves flat, 3-7 nerved, 1.5-3.5 mm wide; achene keeled Potamogeton friesii 
11b. Leaves often rolled, 3 or rarely 5 nerved, .5-2 mm wide; achenes not keeled Potamogeton strictifolius 
12a. Leaves all submersed and similar, cordate or subcordate at base and abruptly sessile or clasping 13 
12b. Leaves usually of 2 kinds, submersed and floating, the floating sometimes not developed, the submersed tapered to base or petioled  15 
13a. Leaves finely serrulate, at least on the upper half, 3-5 mm wide, resembling lasagna noodles.  Invasive species listed as a noxious weed in the state of Montana.  This email address is being protected from spambots. You need JavaScript enabled to view it. Potamogeton crispus 
13b. Leaves entire, mostly over 12 mm wide 14 
14a. Tip of leaves shaped like the bow of a boat, blades mostly 10 cm or more long  Potamogeton praelongus 
14b. Tip of leaves flat, the blades mostly less than 10 cm long Potamogeton richardsonii 
15a. Submersed leaves thread-like or ribbon-like with nearly parallel sides 16 
15b. Submersed leaves broader, the sides curved and not parallel 18 
16a. Submersed leaves 3-10 mm wide  Potamogeton epihydrus 
16b.  Submersed leaves .5-2 mm wide  17 
17a. Floating leaves .7-3 cm long, 5-15 nerved; coiled form of embryo visible in fruit  Potamogeton diversifolius 
17b. Floating leaves mostly 5-10 cm, 15-35 nerved; coiled form of embryo not visible in fruit  Potamogeton natans 
18a. Floating leaves 30-50 nerved; upper submersed leaves mostly 7-20 cm long Potamogeton amplifolius 
18b. Floating leaves less than 30 nerved; upper submersed leaves often smaller  19 
19a. Submersed leaves with petioles 2-13 cm long; mature spike 4 cm or more long Potamogeton nodosus 
19b. Submersed leaves not petioled or with short petioles mostly less than 2 cm long; mature spike mostly 3 cm or less long  20 
20a. Floating leaf blades, if present, reddish tinged, usually long-tapering at base, 7-15 nerved; petioles 2 cm or less long Potamogeton alpinus 
20b. Floating leaf blades usually greenish, often rounded at base, 13-29 nerved; petioles often over 2 cm long 21 
21a. Submersed leaves 1-15 mm wide, 5-30 times as long as wide; mostly 3-9 nerved; petioles of floating leaves mostly longer than blades; stipules prominently keeled  Potamogeton gramineus 
21b. Submersed leaves 15 mm or more wide, 3-5 times as long as wide; mostly 9-19 nerved; petioles of floating leaves mostly shorter than blades; stipules faintly keeled Potamogeton illinoensis 
1 Polygonum amphibium