Micranthemum micranthemoides, formerly Hemianthus micranthemoides, is classed as an annual or as a marsh plant.2 It is known only from the eastern USA between Virginia and New York, where this delicate, creeping plant grew along tidal lower reaches of rivers on banks exposed at low water.12 As it has not been recorded in the wild in recent times and the last herbarium specimen dates from 1941, it is considered missing, possibly even extinct.1 The true species has probably never made it into aquariums.1
The pearlweed that long circulated under its name, and is still sometimes sold as such, is a misidentification: it is Micranthemum glomeratum (Hemianthus glomeratus), a species common in Florida.134 This fast-growing stem plant branches profusely, bears small, bright green leaves and can be grown into dense bushes in the midground.45
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