Duckweed is the common name of lemna minor. The fronds are usually cohering in threes and fours. The fronds are rather thick.
L. H. Bailey Standard Cyclopedia of Horticulture (New York, New York: The MacMillan Company, 1917)
673×2400, 288.6 KiB
287×1024, 23.3 KiB
179×640, 12.4 KiB
89×320, 4.9 KiB