Montana Field Guide

PLANTS: Perennial, free-floating, aquatic herbs. Individuals are called 'fronds' consisting of part stem and part leaf blade. Plants grow singularly or in clusters of 2-5 or more fronds (colonial). A mother frond attaches to new fronds by a stipe or stalk. Source: Landolt in Flora of North America (FNA) 2000.

FRONDS: Usually green, but lower surface is sometimes red or purple. Nearly oval (obovate), 1-8 mm long, and 1 to 1.5 times as long as wide. Margins entire. Swollen on one side (gibbous) with a prominent air space greater than 0.3 mm long. Produces a single root, up to 15 mm long. 3-7 veins radiate from the node. Sources: Landolt in FNA 2000; Giblin et al. [eds.] 2018.

INFLORESCENCE: Flowers rather frequently. When present 1 to 2 bisexual flowers occur in a marginal cleft of the frond. Flowers surrounded by a small utricular, membranous scale. Source: Landolt in FNA 2000.

Lemna is the Greek word for "water plant" and was used by Theophrastus, who often is considered the 'father of botany' (371-287 BC); Lemna might be derived from limne meaning lake which is a common habitat (Giblin et al. [eds.] 2018).

Inflated Duckweed flowers relatively frequently (Landolt in FNA 2000). Across its North American distribution flowering occurs from spring to fall (Landolt in FNA 2000).

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.

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.

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: 0.8-1mm long. Seeds with 8-15 distinct ribs.
*Habitat: Permanent, slow moving water of ponds, lakes, and streams.

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.

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.

Eutrophic, quiet waters in temperate regions (Landolt in FNA 2000). Quiet ponds (Hellquist et al. 2014).

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).

Of all the flowering plants, members of the Duckweed Family are the smallest and have the most reduced flowering parts (Landolt in FNA 2000). There are few characteristics that are noticeable to humans that help distinguish species (Landolt in FNA 2000). Many morphological features are modified among the species. Inflated Duckweed flowers relatively frequently, which is unique for the family; cloning is also common (Landolt in FNA 2000).

FLOWER
Sepals and petals are absent (Landolt in FNA 2000). Stamen number is 1-2. The single ovary has 1 cavity (locule) and is bottle-shaped, tapering into short styles and a funnel-shaped stigma. Ovules range from 2-7.

FRUIT
Follicle is 0.6-1 mm long and laterally winged. It bursts open to disperse 1-5 long-shaped seeds (Landolt in FNA 2000). Seeds have 8-16 distinct ribs.

LIFE CYCLE
Although plants are perennial, species of Duckweed live only as long as the conditions are favorable (Landolt in FNA 2000). Inflated Duckweed populations may persist longer than other species because it can live in a warm spring (Landolt in FNA 2000). Populations move around over time, often facilitated by animal transport.

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).

Threats have not been documented.
Potential threats could include recreational activities that disturb warm spring habitats.