Stems erect to reclining, to 6 m; ribs 9-11. Spines 7-9 per areole, pink when young, becoming brown tipped, to 1 cm. Flowers: flower tube 10-15 cm, smooth or scarcely ridged; scales turgid, with axillary tufts of hairs; hairs tawny brown, stiff, 6-10 mm; buds with brown hairs. Fruits dull yellow at maturity, spheric, 65-75 mm diam. Flowering spring-summer. Coastal hammocks, shell mounds; of conservation concern; 0 m; Fla. According to D. F. Austin (1984), Harrisia aboriginum and H. simpsonii are weakly separated, differing primarily in fruit color, which remains yellow in H. aboriginum while turns to red at maturity in H. simpsonii. Harrisia aboriginum has been found on pre-Columbian, aboriginal shell mounds, hence the specific epithet.