Lemnaceae - Images of Lemna perpusilla
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Lemna perpusilla

A. Lateral view of mature plant body showing one budding pouch at basal end. Dorsal (upper) surface has prominent apical papule near apex, and nodal papule at basal end, just above point where root is attached (there may be 2-3 papules in this region); B. View of underside showing root attachment at basal end, 3 faint veins (nerves) and region of air spaces (aerenchyma); C. Close-up view of basal root sheath (where root is attached to plant body) showing 2 lateral, wing-like appendages. Only L. perpusilla and L. aequinoctialis have these 2 prominent, wing-like, lateral appendages on their basal root sheaths. In addition, their roots are only about 3 cm long, shorter than most other North American species of Lemna. [Illustration by Elaine M. Collins].

Underside of Lemna aequinoctialis showing winged root sheath near the basal attachment node. This species has one prominent apical papule on the upper side. The closely-related L. perpusilla of the eastern United States also has a root sheath with 2 lateral wing-like appendages at the base.

Seeds of Lemna perpusilla collected on Staten Island by Steve Young, Botanist at the New York Natural Heritage Program. The seeds are similar to the tropical L. aequinoctialis, except they have twice as many faint, longitudinal ribs. Both L. perpusilla and L. aequinoctialis readily produce seeds, compared with most other duckweed species. Seeds of L. perpusilla can overwinter in cold climates, while those of L. aequinoctialis generally germinate quickly in warmer waters. In addition, L. aequinoctialis does not produce flowers and fruit in cooler climates. The seeds of both species are less than one mm in length. Compare the seeds of L. aequinoctialis in the following image.

Seeds of Lemna aequinoctialis collected by Mr. Wolffia on the Island of St. John (U.S. Virgin Islands). They are small enough to easily pass through the "eye" of an ordinary sewing needle. Note the longitudinal ribs on the seeds. In the closely related Lemna perpusilla, the seeds have up to twice as many faint longitudinal ribs. Since seeds are rarely collected, they are not very useful in identifying species of duckweeds.

Seeds of an unidentified Lemna, probably L. aequinoctialis. Seven
longitudinal ribs (marked by red dots) can be seen in the right seed.

Microscopic view of the seeds of Lemna perpusilla compared with cuboidal grains of ordinary table salt (NaCl). Each seed has numerous longitudinal ridges that appear like faint parallel lines. The apex of each seed has a pointed operculum. The seeds are produced in one-seeded fruits called utricles with thin, membranous pericarps (fruit walls). Although they are minute, the world's record for smallest fruit goes to certain species of Wolffia (incl. W. globosa and W. angusta) with fruits the size of duckweed seeds.

The world's smallest fruits are produced by species of Wolffia, including the Australian W. angusta. The above image shows a mature fruit within the plant body. The larger fruit of Lemna shows a thin, transparent pericarp surrounding a ribbed seed. A pericarp layer is not evident on the wolffia fruits.

Wolfia: The World's Smallest Fruit

Microscopic view of three cuboidal grains of ordinary table salt (sodium chloride or NaCl). All three grains are just over one millimeter in length (red bar). Grains of table salt vary slightly in size, but three average grains stacked together adds up to approximately one mm. If three grains equal one millimeter in length, then a single grain is approximately 0.3 mm or 0.03 cm on a side.

See Straight Pin & Sewing Needle Used In Wayne's Word Articles

Lemna perpusilla Seedlings With Attached Seeds

Germinated seeds of Lemna perpusilla showing seedlings with attached seeds.

Germinated seeds of Lemna perpusilla showing seedlings with attached seeds.

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