Deepwater open-circuit scuba, dredging, submersible, and technical mixed-gas (closed-circuit) rebreather diving collections of marine benthic algae made over the last approximately 30 years in Puerto Rico are summarized in this account. In total, 186 taxa (166 identified to species) comprising 60% Rhodophyta, 11% Phaeophyceae, and 29% Chlorophyta are reported from depths greater than 35 m. Eighty-nine of these (56% of taxa identified to species) from the Puerto Rican mesophotic are thought to be the deepest known distributional records for the species recognized. Forty-three species (8% of the entire benthic flora of Puerto Rico) are mostly or entirely restricted to depths greater than 35 m.