Colonies are branching, each clump being much more irregular than Madracis auretenra. Also the branches also get much longer so the overall colony size is larger. Cross sections of branches are irregular rather than round, and incipient branches cause their tips to become lumpy and club-shaped.

Colour is green, yellow-green, yellow-brown or tan. Polyps are yellow in this species but not in M. decactis. Branches are usually longer than M. decactis but thicker than M. auretenra.

Corallites usually have 8 septa, unlike M. decactis and M. auretenra, which both have 10. It is easily confused with Madracis carmabi, which has the same morphology and which also has 10 septa and is considered by some to be a hybrid species.