"D. tropica" is in the section Herbacea of "Desmarestia", but compared to other North American species it is less membranous. Tropical acidweed has been found in only two locations: Post Office Bay off Floreana Island and Caleta Tagus (Tagus Cove) off Isabela Island. At the former site it was found at depths from . It was once thought to be found off the mainland coast of Peru, but these specimens are considered instead to be "D. firma". Despite its tropical range, it prefers the cold, deep water of upwelling areas of the lower sublittoral zone.