Adenostemma brasilianum is an herbaceous asteracean pollinated by male Ithomiinae butterflies. These insects feed on the nectar, which contains pyrrolizidine alkaloids, and depend on these compounds for their defense and reproduction. The life history of this species was described from seedlings to the death of adult plants. In addition, we analyzed its reproductive phenology and identified herbivores. The study was conducted in southeastern Brazil, in a semideciduous seasonal forest fragment. Fifty plants with up to two pairs of well-defined leaves were monitored, on which we observed buds, flowers, dispersed diaspores, and herbivores. We labeled 140 capitula in the bud stage and monitored them from anthesis of the first flowers to diaspore dispersal. Adenostemma brasilianum is biennial and monocarpic, and establishes a seedling bank within about 9 months (from February to October, in the first year of life). Plant mortality resulting from physical damage was high (46%) at the beginning of the rainy season (from November to December of the first year). At that time, the remaining plants entered the reproductive phase, which lasted until June (the dry season of the second year). In the capitula, the flowers open in a centripetal sequence for four consecutive days. In the first 2 days, 74% of the flowers were in anthesis. On the 20th day of the capitulum, the diaspores were completely exposed. Dispersal began in January (second year). Due to the pappus with viscid glands, diaspore dispersal is epizoochorous, which is an unusual feature among Asteraceae. Herbivory occurred mainly at the end of the reproductive period (July) until plant death (December), in the second year of life. Herbivores were the beetles Agathomerus signatus, Elytrosphoera xarthopyga, and Homophoeta octoguttata. In conclusion, in the short life history of A. brasilianum, abiotic (associated with the maintenance of the seedling bank, plant growth, and mortality) and biotic factors (associated with pollination, dispersion, and herbivory) act in synergy to complete the plant cycle.