Alisma L.
Perennial aquatic herbs, rarely submersed. Leaves erect, plantain-like, or rarely floating, long-petioled. Inflorescence a much-branched, pyramidal panicle; each branch with 2-3 papery basal bracts. Flowers many, pedicellate; each pedicel bracteate at base; sepals 3, green, persistent; petals 3, > sepals, white or occasionally rose or pink. Stamens 6-9. Achenes free, numerous, in a single whorl round flattened receptacle. Spp. c. 9, in north temperate regions and Australia. Adventive spp. 2.
Key
1
Leaves broad-ovate to ovate-lanceolate, usually rounded or subcordate at base; petals rounded-truncate; style usually arising below middle of fruit, ± straight
Leaves lanceolate, gradually narrowed at base; petals ± acute; style usually arising above middle of fruit, curved in lower part
