Poaceae in the Robinson Crusoe (=Juan Fernández) Islands number 53 species in 32 genera, of which 9% of the species are endemic, 9% indigenous, and 81% adventitious. The endemic taxa (and their conservation status) are: Agrostis masafuerana (rare), Chusquea fernandeziana (not endangered), Megalachne berteroana (not endangered), M. masafuerana (not endangered), and Podophorus bromoides (extinct). Megalachne and Podophorus are endemic genera. Comparisons with Poaceae in the Bonin and Volcano Islands, Canary Islands, Galápagos Islands, and Hawaiian Islands show different levels of endemism: number of endemic taxa, respectively, 5, 10, 12, 40; percent specific endemism, 8, 6, 21, 19. No endemic genera occur. Anthoxanthum odoratum, Avena barbata and Hordeum murinum are noxious weeds in the Robinson Crusoe Islands. Many adventives are shared among floras of the archipelagos, with the highest ties of Robinson Crusoe being to the Canaries (53% of total Poaceae known in Juan Fernández) and the Hawaiian Islands (47%). Low levels of adventives occur within the Bonin (5%) and Galápagos (7%) Islands. In contrast, there are many endemic genera of Asteraceae in these same archipelagos: Bonin and Volcano Islands (1), Canary Islands (8), Galápagos Islands (5), and Hawaiian Islands (6); percent of specific endemism is also higher (20, 53, 54 and 56, respectively). Hypotheses for greater levels of endemics among oceanic island Asteraceae include more efficient dispersal mechanisms by wind and birds, animal pollination systems that result in greater degrees of geographic populational genetic isolation, and a vascular cambium that offers enhanced growth-form evolutionary opportunities.