Atmospheric CO 2 enrichment can affect plants directly via impacts on their performance, and indirectly, by environment-specific traits passed down from the mother plant to the offspring. Such maternal effects can significantly alter plant species composition, especially in annual ecosystems where the entire community is recruited from seeds each year. This study assessed impacts of future, high CO 2 (440 and 600 ppm) and pre-industrial, low CO 2 (280 ppm) on seed traits and offspring performance in three plant functional groups (grasses, legumes, forbs) comprising 17 annual species of a semi-arid Mediterranean community. In grasses, seed size and seed-reserve utilization as expressed by root elongation tended to be higher at high than at low maternal CO 2, but total seed protein concentration and protein pool decreased with increasing maternal CO 2. The response of seed size to high CO 2 increased with increasing leaf-mass fraction in grasses, and decreased with decreasing concentration of leaf non-structural carbohydrates in legumes. Offspring development was studied at ambient CO 2, and showed reduced emergence success of high-CO 2 progeny compared with low-CO 2 progeny in forbs. Total biomass was lower in high-CO 2 than in low-CO 2 offspring across all functional groups. The biomass response to high maternal CO 2 in legume offspring correlated inversely with seed size, resulting in up to 25% lower biomass in large-seeded species. Under the scenario of maternal effects combined with projected changes in biomass and seed production under direct exposure to high CO 2, legumes might gain and forbs and grasses might lose from future CO 2 enrichment. Most changes in seed traits and offspring performance were greater between pre-industrial and near-future CO 2 than between near- and remote-future CO 2 concentrations. Hence, maternal effects of increasing CO 2 may contribute to current changes in plant productivity and species composition, and they need to be considered when predicting impacts of global change on plant communities.