Mapping is provisional. Further records may be expected from closer study of material filed under punctata. P. robustior is a widely scattered perennial in eastern North America and it extends to South America. However, it is concentrated on "peaty shores" in coastal regions and uncommon to rare in several states (FNA 5, K, W). It differs from punctata in its inflorescences, which are uninterrupted (versus interrupted); its ocreolae are overlapping (versus mostly not), their margins with hairs lacking or sometimes up to 1 mm long (versus mostly with hairs up to 2 mm); its leaves are 2-4.5 cm wide (versus 0.6-2.4 cm). Under Polygonum, the epithet has been spelled robustius.