Lilaeopsis, commonly known as grassworts, microswords, or water umbels, is a genus of aquatic and riparian flowering plants belonging to the family Apiaceae (order Apiales) — the same family as carrots, celery, and parsley. The genus comprises around 12 accepted species of small, grass-like plants with hollow, jointed leaves and a low, creeping growth habit that spreads via rhizomes across mudflats, stream margins, and shallow water.
The genus is distributed primarily along the Pacific coast of the Americas, ranging from southern Alaska south to Tierra del Fuego, Patagonia, and the Falkland Islands, with additional species occurring across mainland Australia, New Zealand, Tasmania, and several Caribbean and oceanic islands. One species, Lilaeopsis mauritiana, reaches the Indian Ocean islands of Madagascar and Mauritius.
Several species are native to North America: Lilaeopsis chinensis (Eastern grasswort) extends from Eastern Canada to southeastern Texas, while Lilaeopsis occidentalis (Western grasswort) spans the Pacific coast from Alaska south through Colombia, Ecuador, Peru, and Chile. Lilaeopsis novae-zelandiae is native to Tasmania and the South Island of New Zealand.
The genus has gained particular attention in the aquascaping hobby through Lilaeopsis minor (synonym L. brasiliensis, microsword or Brazilian microsword), whose grass-like appearance and dense mat-forming habit make it a popular foreground groundcover plant in planted aquaria. It is commercially propagated via tissue culture. The genus as a whole performs best in a nutrient-rich organic substrate, well-aerated water, and medium to high light; carbon dioxide supplementation further improves growth and vigour.
Distribution
Lilaeopsis is found primarily along the Pacific coast of the Americas, from southern Alaska south through the Andes to Tierra del Fuego, Patagonia, and the Falkland Islands, with several species also occurring in eastern North America. The genus extends to mainland Australia (Queensland, Victoria, South and West Australia), Tasmania, New Zealand, and a handful of Caribbean and oceanic islands. One species, L. mauritiana, has a disjunct range on Madagascar and Mauritius in the Indian Ocean.
Ecology
Species of Lilaeopsis are aquatic to riparian herbs that colonise mudflats, tidal margins, stream banks, and shallow freshwater or brackish habitats. Their hollow, jointed leaves and rhizomatous growth allow them to form dense mats in waterlogged or seasonally inundated substrates. The genus tolerates a range of light conditions but favours well-aerated water and organic-rich sediments.
Cultivation
In cultivation, Lilaeopsis species grow best in a nutrient-rich organic substrate (such as aquasoil or loam-based compost) rather than plain sand or gravel. They require medium to high light — natural light or artificial lighting of equivalent intensity — and perform well in well-aerated water. Carbon dioxide supplementation accelerates growth and improves vigour, though it is not strictly necessary when the substrate is sufficiently fertile. Lilaeopsis minor is the most widely cultivated species and is commercially available in tissue-culture form, making it easy to establish in aquaria free of algae and pests.
