Alismataceae

Defining Characteristics

• Aquatic or semi-aquatic herbs of freshwater habitats
• Flowers with 3 white or pink petals, 3 green sepals — trimerous and actinomorphic
• Numerous free (unfused) carpels, each producing a single-seeded achene — aggregate fruit
• Leaves often with sagittate (arrow-shaped), ovate, or linear blades; heterophylly common (different leaf shapes submersed vs. emersed)
• Latex-producing canals present in vegetative tissues
• Inflorescence usually a raceme or panicle of whorled branches

Notable Genera

• Alisma (water-plantains)
• Sagittaria (arrowheads)
• Echinodorus (sword plants — aquarium staples)
• Helanthium (dwarf swords, formerly in Echinodorus)
• Hydrocleys (water poppies)

Notes

A small but ecologically and horticulturally important family of obligate aquatic/wetland plants. Echinodorus and Sagittaria are among the most widely cultivated genera in the aquarium trade — 'Amazon swords' (Echinodorus) are centerpiece plants in countless planted aquaria. Sagittaria species (arrowheads) produce edible tubers and were an important food source for Indigenous peoples of North America. Many species exhibit dramatic heterophylly: submersed leaves are ribbon-like, while emersed leaves develop broad blades.