Scanning electron microscopy (SEM) observations of seed samples of 75 species representing fourteen Pitcairnioideae genera combined with some seed developmental and germination data revealed six classes of seed morphology (the Dyckia type, Puya ferruginea type, Puya hamata type, Fosterella type, Navia type and the Brocchinia type). Overall seed shape, nature of the appendage, presence or absence of visible demarcation between the body and appendage, surface cellular pattern and the permanency of the appendage were especially useful for distinguishing the seed types. Taxonomically, seed characteristics are correlated with other features in indicating a close relationship between i)EncholiriumandDyckia, ii)Fosterellaand the Guayana Highland generic group (Ayensua, ConnelliaandCottendorfia) and iii)PepiniaandPuya, and within the species of Puya hamata complex. Seed morphology suggests an isolated position forBrocchiniawithin the subfamily. Phylogenetically, seeds of the Fosterella and Puya ferruginea types represent putative homoplasies due to the reversals and parallelisms in different groups. Other seed types are unique to their lineages. Some putative phyletic transformations of the Brocchinia and Navia type seeds correspond with those of the Tillandsioideae and Bromelioideae, respectively.