Pearl weed

Water parameters

Light and nutrients

Substrate type: nutrient rich. Propagation: cuttings.

Substrate compatibility

With fish

Origin and habitat

The aquarium 'pearl weed' is, in current understanding, Micranthemum glomeratum (synonym Hemianthus glomeratus), family Linderniaceae, the manatee mudflower, native to Florida and the southeastern US. For decades it was sold under the name Hemianthus or Micranthemum micranthemoides, but that name belongs to Nuttall's mudflower, a mid-Atlantic US plant (Virginia to New York) presumed extinct in the wild since 1941; herbarium comparison showed the trade plant is the Florida species instead. So the old 'native to Cuba and the Caribbean' attribution is incorrect. Pearl weed is a small-leaved stem plant with tiny oval bright-green leaves a few millimetres long in whorls of three along thin upright stems, forming dense bushy masses, and is valued for being able to act as either a midground bush or, trimmed short, a foreground carpet.

Care notes

Easy to moderate. It grows in low to high light, with or without CO2. Under strong light with CO2 it grows fast and can be trimmed into a tight foreground carpet a centimetre or two tall, while in moderate light without CO2 it makes a bushy 5–15 cm midground plant; which role it plays is set entirely by how you trim it, short for carpet, long for bush. Plant stems in groups pushed into the substrate, trim often, and the cut stems throw many side shoots, getting denser each cycle. The fine bright-green texture fills gaps between larger leaves and hardscape. Keep it around 20–28°C in soft to moderately hard water, and dose moderate nutrients, since starved older leaves yellow and drop. Its versatility, filling carpet, midground or background depending on maintenance, is its main appeal, and the dense growth shelters fry and grazes shrimp. It is an ornamental, not a crop, so it is unsuited to media-bed aquaponics or hydroponics.

Further reading

• Keeping shrimp with fish: what actually works