Montana Field Guide

Frond ovate, 1–8 mm long; solitary or in small clusters, often purplish on the lower surface. Roots 1–15 mm long (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Montana species of the Duckweed Family are all small, perennial, free-floating, aquatic herbs distinguished by their veins and roots. Veins are best observed using a 10x magnification and back-lighting (Giblin et al. [eds.] 2018) or by placing on a transparent slide (Landolt in FNA 2000). Landolt in FNA (2000) provides some techniques to analyze anatomy. In this family the term "leaf" cannot be used because a leaf consists of a stem (petiole) and a blade (Landolt in FNA 2000). Instead the term "frond" is used. Be aware that species can grow in the same place naturally.

Lemna - Duckweed, native
* Fronds: Green above and mostly below.
* Root: 1 per frond, sometimes absent.
* Veins: 1-3 per frond.

Spirodela - Duck-meal, native
* Fronds: Green above and usually purplish below.
* Roots: 2 or more per frond
* Veins: 3 or more per frond.

Wolffia - Water-meal, native
* Fronds: Green to brown.
* Root: 0; absent.
* Veins: 0; absent.

Lesser Duckweed - Lemna minor, native
*Compare to Lemna turionifera.
*Fronds: at least some are more than 2 mm long, roundish, green on top and often purplish on bottom.
*Turions: Absent.
*Fruit: 0.8-1 mm long. Seeds with 8-15 distinct ribs.
*Habitat: Permanent, slow moving water of ponds, lakes, and streams.

Turion Duckweed - Lemna turionifera, native
*Compare to Lemna minor.
*Fronds: 1-4 mm long, nearly oval, flat, green on top and bottom, sometimes red to purplish on bottom. Red to purple color emanating from the root.
*Turions: Produced under stress. Olive, brown, or dark green rootless disk-like, 0.8-1.6 mm wide, that sink.
*Fruit: 0.5-0.6 mm long. Seeds with 30-60 distinct ribs.
*Habitat: Calm waters.

Pale Duckweed - Lemna valdiviana, native, SOC
*Fronds: 1-2 mm long, oblong, green on top and bottom.
*Turions: Absent.
*Habitat: Warm Springs; possibly also lakes and rivers.

Inflated Duckweed - Lemna gibba, native
*Fronds: Less than 6 mm long, nearly oval, greenish on top and bottom or red to purplish on bottom. Red to purple color emanating from the margins.Inflated which can be seen in cross-section, making their lower surface convex.
*Turions: Absent.
*Habitat: Calm waters of ponds and lakes.

Star Duckweed - Lemna triscula, native
*Fronds: 6-12 mm long, oblong to lanceolate and attached together by elongated stipes to appear like a 'canoe paddle', and greenish on top and bottom.
*Turions: Absent.
*Veins: 3 and faint.
*Habitat: Fresh to somewhat alkaline water of ponds, lakes, and marshes.

Permanent fresh water of ponds, lakes, slow streams; plains, valleys, montane (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

GROWTH
Duckweed plants that grow in shaded habitats may be twice the size of those growing in full sun (Giblin et al. [eds.] 2018). Members of the Duckweed Family have a high productivity rate with particular species able to double their population with a 24-hour window (Landolt in FNA 2000). Species of the Duckweed Family tend to be very rare in places with high or very low precipitation (Landolt in FNA 2000).

PLANT-ANIMAL INTERACTIONS
Plants in the Duckweed Family are easily transplanted over short distances by birds (Landolt in FNA 2000). Duckweed species have a high nutritive value with up to 45% of their dry weight consisting of amino acids, the building blocks for protein (Landolt in FNA 2000; Culver and Lemly 2013). They provide food for fish, snapping turtles, and waterfowl and create habitat for aquatic invertebrates (Culver and Lemly 2013). Certain species are cultivated as feed for poultry, pegs, and cows (Landolt in FNA 2000).

Species of the Duckweed Family are used for waste-water purification and as test- and indicator- plants for detecting certain conditions (Landolt in FNA 2000).