They are followed by seed pods which hold flat, shiny black seeds ripening in late summer. Z. americanum has flowers with red tipped green petals born in axillary clusters. Z. americanum are pubescent on lower surface. Z. coriaceum has even pinnate leaves. The sharp thorns along the leaves, branches and young trunks are identifying characteristics.
Older trunks lose the thorns, but have bumps on the bark.
Z. americana is distinguished by thorns mostly in pairs at the nodes rather than along the stem. Z. clava herculis is found in wet woods and hammocks nearly throughout Florida, following the coastal plain to Texas and Arkansas and north to Virginia. See first paragraph for other species.