Orbicella franksi is one of three species of Orbicella coral found in the Caribbean. This species of Orbicella grows into large plates covered in irregularly shaped nodules. The three species of Orbicella are O. faveolata, O. annularis, and O. franksi.
The corallites are conical and irregular in shape and size, 2.5-4 mm diameter and formed by extratentacular budding. The color is orange-brown, greenish-brown or greyish-brown, but the extremities of the lumps are often pale or white.
O. franski is also called the boulder star coral, and it very similar in appearance to other Orbicella species. The biggest difference with this coral is the corallite structure form clumps and make an uneven surface. This is the least common of all Orbicella species.
Similar Species: Orbicella annularis is similar with more columnar or nodular colonies and corallites are not conical. Orbicella faveolata has smaller, less exert corallites and septa in two unequal orders.
This coral forms plates, and under ledges or is shady areas may be encrusting. We found this huge colony of brown Orbicella in the Cayman islands under the side of a ridge and the coral covered several meters of reef.