water chestnut flower; water caltrop flower
Refers specifically to the flower of the water chestnut (Trapa japonica) or water caltrop. A botanical term; in everyday contexts, the plant itself is usually called 菱 (ひし).
See also: 菱
Water chestnut flowers are blooming on the summer pond.
Compound of 菱 (りょう, water chestnut) + 花 (か, flower). The reading りょう for 菱 is the on'yomi, used in formal or compound contexts.