The longevity and long-term storage of Passiflora seed are investigated. Dehydrated seed were stored at temperatures from 30°C to -196°C for periods of up to five and a half years. It was determined that seed from most species should be treated as semiorthodox for seed storage purposes, but seed from species in the section Quadrangularis should be treated as semi-recalcitrant. High temperatures during fruit maturation of P. subpeltata were shown to induce seed coat-imposed dormancy. The presence of seed coat-imposed dormancy was confirmed in seed of two other Passiflora species. Prolonged periods of seed washing in tepid water were shown to be successful in breaking seed coat-imposed dormancy. Factors influencing the successful germination of quiescent Passiflora seed were investigated. The seed coat morphology of Passiflora species produced by interspecific hybridisation was found to be in keeping with the variations found in seed produced by intra-specific hybridisation. The seed coat morphology of Passiflora cultivars was found to be an intermediary of the seed coat morphology of their parents. A new classification of the genus Passiflora using only the morphological features of their seed is presented using seed from 360 accessions. The results of this study support the karyotypic evidence of x = 6 and x = 9 and otherwise shadow the conventional taxonomic classification of Passiflora, with the exception of species in the subgenus Astrophea and sections Quadrangularis, Serratifolia, Passiflora, and Tiliifolia in the subgenus Passiflora. The seed coat morphology of Passiflora species is compared with that of Adenia species and the probability of parallel evolution of Passiflora from several ancient archetypal Adenia species is proposed. Aspects of the sociology and ecology of Passiflora species are presented. Evidence of insect and plant mimicry is demonstrated. Detailed descriptions of new Passiflora species and subspecies are presented.