Lemna

Roots 1 per frond. Fronds floating or submersed, 1 or 2–20 or more, coherent in groups or forming chains, lanceolate-ovate, flat or gibbous, 1–15 mm, margins entire or denticulate, upper surfaces sometimes with small conic papillae along veins (especially at node and near apex); air spaces in tissue; reproductive pouches 2, lateral, at base from which daughter fronds and flowers originate, triangular; veins 1–5(–7), originating from point in proximal part of frond (node) or if more than 3 veins present, outer ones sometimes branching distally from inner ones; scale at base of frond absent; anthocyanins sometimes present; pigment cells absent (red pigmentation present in some species); turions absent (sometimes present in L. turionifera). Flowers 1(–2) per frond, surrounded by small utricular, membranous scale; stamens 2, 4-locular. Seeds 1–5, longitudinally ribbed. x = 10, 21, 22

Distribution

Worldwide except arctic and antarctic regions.

Discussion

In Lemna the connection to the mother frond is formed by a thin white stipe at the base that falls off or decays after the frond is grown (frond of L. trisulca is narrowed at base into a green stalk persisting on frond).

Species 13 (9 in the flora).

Selected References

None.

Lower Taxa

Lemna aequinoctialis, Lemna gibba, Lemna minor, Lemna minuta, Lemna obscura, Lemna perpusilla, Lemna trisulca, Lemna turionifera, Lemna valdiviana

Key

1	Fronds submersed (except when flowering or fruiting), margins denticulate distally, 2–3.5 times as long as wide, base suddenly narrowed into green stalk, 2–20 mm.	Lemna trisulca
1	Fronds floating, margins entire, 1–3 times as long as wide.	> 2
2	Fronds with 1 vein.	> 3
2	Fronds with 3–5(–7) veins.	> 4
3	Vein mostly prominent, longer than extension of air spaces, or running through at least 3/4 distance between node and apex	Lemna valdiviana
3	Vein sometimes indistinct, very rarely longer than extension of air spaces, not longer than 2/3 distance between node and apex	Lemna minuta
4	Root sheath winged at base; root tip usually sharp pointed; roots to 3(–3.5) cm; fronds without reddish color or spots of anthocyanin, mostly with 1 very distinct papilla near apex on upper surface.	> 5
4	Root sheath not winged; root tip mostly rounded; roots often longer than 3 cm; fronds often with reddish tinge or spots of anthocyanin, with or without distinct papilla near apex on upper surface.	> 6
5	Seeds with 35–70 indistinct ribs (to count ribs remove membranous pericarp), staying within fruit wall after ripening; root sheath wing 2–3 times as long as wide	Lemna perpusilla
5	Seeds with 8–26 distinct ribs, falling out of fruit wall after ripening; root sheath wing 1–2.5 times as long as wide	Lemna aequinoctialis
6	Plants forming small, olive to brown, rootless turions, which sink to bottom	Lemna turionifera
6	Plants usually without distinct turions.	> 7
7	Largest air spaces longer than 0.3 mm; if red-colored on lower surface, coloring beginning from margin; ovary (1–)2–7-ovulate	Lemna gibba
7	Largest air spaces 0.3 mm or shorter; if pigmented on lower surface, red coloring beginning from attachment point of root; ovary 1-ovulate.	> 8
8	Fronds not reddish on lower surface (or at least much less so than on upper); greatest distance between lateral veins near or proximal to middle.	Lemna minor
8	Fronds often reddish on lower surface (more intensely so than on upper); greatest distance between lateral veins near or distal to middle.	> 9
9	Fronds flat, with mostly distinct papillae on midline of upper surface; seeds with 30–60 indistinct ribs	Lemna turionifera
9	Fronds often gibbous, with very distinct papillae above node and near apex on upper surface but not between node and apex; seeds with 10–16 distinct ribs	Lemna obscura