A low-growing, annual, marginal plant, Crassula aquatica (family Crassulaceae), of North America and Europe; (later also, with distinguishing word) any of several other small crassulas.
Origin
Early 19th century; earliest use found in Amos Eaton (1776–1842).
Definition of pygmyweed in US English:
pygmyweed
noun
A low-growing, annual, marginal plant, Crassula aquatica (family Crassulaceae), of North America and Europe; (later also, with distinguishing word) any of several other small crassulas.
Origin
Early 19th century; earliest use found in Amos Eaton (1776–1842).