Cyathea atrocastanea, a new species of tree fern is described, illustrated, and compared with similar species. This new species should be classified as vulnerable (VU) according to the IUCN criteria. This species is distinct by its atrocastaneous and scurfy petiole, and
rachis, and by the broad ovate and yellowish, nonbullate scales on the costulae and midveins. A key to the exindusiate species from southeastern Brazil with nondenticulate petiole scales is also presented.