Alismatales

Alismatales is an order of flowering plants within the monocots that is characterized primarily by aquatic or marsh-dwelling members. In modern classifications, the order is placed among the alismatid monocots and is noted for its repeated adaptations to freshwater and coastal habitats. The circumscription of Alismatales has varied over time as molecular phylogenetic studies have refined relationships among aquatic lineages.

Plants in Alismatales are commonly herbaceous and aquatic, often with rhizomes or stolons that help anchor them in soft substrates. Leaves are frequently simple and linear or lanceolate, sometimes with special adaptations for buoyancy or submerged growth. Flowers tend to be small and inconspicuous, and many species have reproductive structures that accommodate their aquatic lifestyles.

The order includes several families that are familiar from wetland and aquatic ecosystems. Notable examples include Alismataceae (water-plantains) and Hydrocharitaceae (which contains several aquatic genera such as Hydrilla and Vallisneria). Other families commonly associated with Alismatales in various classifications include Potamogetonaceae (pondweeds), Cymodoceaceae, Zosteraceae (seagrasses), and Zannichelliaceae, among others. The diversity ranges from freshwater marsh species to fully marine seagrasses in coastal and estuarine environments.

Ecology and distribution of Alismatales are global, with representatives occupying a wide range of aquatic habitats—from rivers and ponds to shallow seas. They play important roles in ecosystem functioning, including water purification, sediment stabilization, and providing habitat for aquatic organisms. Some members, such as certain Hydrocharitaceae, have become invasive in non-native regions, highlighting the ecological and economic relevance of this order.