Key to Myriophyllum

View taxon page for Myriophyllum

(For a list of species in Myriophyllum, use the above link.)

Jepson Manual glossary definitions can be seen by moving your cursor over words underlined with dots.

1. Leaves 

alternate 

1. Arranged singly, often spirally, along an axis - e.g., one leaf per node. 2. Occurring in different ranks, appearing to be between, not directly above or below, as 'stamens alternate petals'.

, or 

whorled 

Arranged in groups of three or more at nodes or positions along an axis (e.g., three leaves per node).

with some scattered single leaves ..... M. hippuroides

1' Leaves whorled (opposite)

2. Plants dioecious; leaves narrow, length 3–4 × width; bracts ± = stem leaves ..... M. aquaticum

2' Plants monoecious; leaves generally wider; bracts < stem leaves.

3. Bracts pinnately dissected; stems green, dark green to ± black-green when dry ..... M. verticillatum

3' Bracts 

entire 

Having margins that are continuous and smooth (i.e., without teeth, lobes, etc.).

or 

dentate 

Having margins with sharp, relatively coarse teeth pointing outward, not tipward.

; stems dark green, occasionally red-tinged; generally ± white to pink or dark gray when dry.

4. Leaves dark green when fresh, darker when dry, glaucous; young shoots with >= 1 pair of entire, 

opposite 

1. Arranged in pairs along an axis - e.g., two leaves per node. 2. Occurring in the same rank, directly above or below, as 'stamens opposite petals'. 3. Located directly across from.

leaves at base; plants conspicuously rhizomed; flower bracts triangular, 4–10 mm, toothed, glaucous ..... M. quitense

4' Leaves dark green when fresh, generally red-tinged, not glaucous when dry, occasionally waxy from diatoms; young shoots lacking pairs of entire, opposite leaves at base; plants not conspicuously rhizomed; flower bracts 

lanceolate 

Narrowly elongate, widest in the basal half, often tapered to an acute tip.

to 

ovate 

Egg-shaped (i.e., widest below the middle) in two dimensions (i.e., in one plane), as a leaf.

or oblanceolate, 1–3 mm, entire to toothed, not glaucous

5. Leaf segments 4–14 pairs; angles, spacing varying throughout 

leaf 

Organ arising from a stem, generally composed of a stalk (petiole) and a flat, expanded, green, photosynthetic area (blade); distinguished from a leaflet by the presence in its axil of a bud, branch, thorn, or flower; sometimes with lateral, basal appendages (stipules); either simple (toothed, lobed, or dissected but not divided into leaflets) or compound (divided into leaflets).

..... M. sibiricum

5' Leaf segments 14–24 pairs; angles, spacing uniform throughout leaf ..... M. spicatum

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