Vascular Plants of North Carolina
Account for Greater Duckweed - Spirodela polyrhiza   (L.) Schleiden
Members of Araceae:
Only member of Spirodela in NC.
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Section 5 » Family Araceae
Author(L.) Schleiden
DistributionNearly throughout the Coastal Plain, though scarce in the southern third of the province, and absent from the Sandhills region. Ranges barely into the northeastern Piedmont, and casual into the western Piedmont (Catawba County).

This is a wide-ranging species, across most of Canada and the U.S., found in all states. However, it is scarce in the Appalachians and most of the Piedmont.
AbundanceReasonably common to common in the northern half of the Coastal Plain, south to Johnston and Craven counties. Rare to uncommon in the southeastern Coastal Plain, but absent in the southwestern portions. Very rare to rare in the northeastern Piedmont, and perhaps historical in the western Piedmont. The NCNHP took the website editors' suggestion to move the State Rank to a more accurate S4 now (2021), but "incorrectly" left the species on its Watch List.
HabitatThis species has the same habitats as other duckweeds (Lemna spp.) -- still or slowly moving waters of pools, ponds, lakes, beaver ponds, and swamps.
See also Habitat Account for General Herbaceous Ponds
PhenologySeemingly does not flower, or seldom does so.
IdentificationThis is a tiny floating plant with flattened stems (fronds), rounded from above. In this genus, there are 7-21 roots per frond (on the underside of each frond); Lemna species have just a single root on each frond. This species has a fairly thick frond, as well, and is purplish below. Note that the former S. oligorrhiza, now named as Landoltia punctata, is an exotic species but is found at a number of Coastal Plain ponds and pools; it has fronds with 2-7 roots and each frond is elliptical (1.5-3 times as long as wide), whereas S. polyrrhiza has 7-21 roots per frond and has a rounded frond less than 1.5 times as long as wide.
Taxonomic CommentsSome references have spelled the name as polyrrhiza.

Other Common Name(s)Great Duckweed, Duckmeat, Great Duckmeat, Common Duckmeat
State RankS4
Global RankG5
State StatusW7
US Status
USACE-agcpOBL link
USACE-empOBL link
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