This southeastern tree occurs mostly in swamps of the Coastal Plain, but it also extends into some larger valleys of the southern Interior Low Plateaus (K). In Ky. it is recorded mostly near the lower Ohio and lower Green Rivers, and remains unknown on the Mississippi lowlands (CARL, HICK & FULT). Along cypress-tupelo sloughs, this species appears to associate with backwaters that have less frequent, or less intense, flooding and alluviation. Hybrids with illinoinensis can be expected (FNA 3, K); these "bitter pecans" have been named X lecontei Little, but application of "texana" has been erroneous. Without flowers or nuts, distinction of aquatica from illinoinensis is sometimes difficult (Sargent 1926; F, Cr, FNA 3, St, W). Bark is somewhat shaggy with moderately broad plates (versus scaly with small exfoliating plates). Leaflets tend to be fewer (usually 7-13 versus 9-19), on shorter petiolules (0-2 mm in laterals versus 0-7 mm), often less strongly serrate to entire (versus often double-serrate), and perhaps more villous below along veins. Terminal buds are reddish-brown to black (versus yellowish-brown) but covered with caducous yellow glands (versus jointed hairs). In both species, lateral (flowering) buds have outer scales that are fused (as in subgenus Apocarya); in cordiformis these scales are free but with margins generally obscured by scales (Y). In all three species, forming subgenus Eucarya, terminal buds are generally elongated and flattened with 4-6 valvate scales (versus ovoid and terete with 6-15 imbricate scales in subgenus Apocarya); but terminal buds in shade are sometimes less elongated and terete; leaflets are mostly 7-13 (versus 5-9), and often strongly falcate in sun (versus no more than slightly so); nuts are narrowly winged (versus winged or not); 2n = 32 (versus 32 or 64).