An end effector for a surgical instrument, comprising: a first jaw having a cartridge body, the cartridge body having on a tissue-contacting surface thereof a plurality of staple cavities configured to seat staples therein, the first jaw having a generally rectangular nominal perimeter defining a regular perimeter around outer rows of the plurality of staple cavities; a second jaw having an anvil with a plurality of staple forming cavities formed on a tissue-contacting surface thereof, wherein at least one of the first and second jaws is movable relative to the other between open and closed positions, the second jaw having a generally rectangular nominal perimeter opposed to the nominal perimeter of the first jaw; a plurality of attachment features (120, 126) formed on at least one jaw of the first and second jaws on extension elements (118, 122) extending beyond the nominal perimeter of the at least one jaw such that each of the extension elements has at least one attachment feature formed thereon; and an adjunct material having a shape complementary to at least one of the first and second jaws and being configured to releasably mate with the attachment features, wherein the adjunct material comprises at least one mating feature that is complementary to at least one of the plurality of attachment features and is configured to releasably mate with the at least one attachment feature; and wherein the extension elements are formed integrally with the at least one jaw, and wherein the at least one of the plurality of attachment features comprises a projection extending perpendicular to a longitudinal axis of the at least one jaw from the corresponding extension element formed on the at least one jaw, and wherein the at least one mating feature comprises a through opening formed in the adjunct material and configured to receive the projection therein. a first jaw having a cartridge body, the cartridge body having on a tissue-contacting surface thereof a plurality of staple cavities configured to seat staples therein, the first jaw having a generally rectangular nominal perimeter defining a regular perimeter around outer rows of the plurality of staple cavities; a second jaw having an anvil with a plurality of staple forming cavities formed on a tissue-contacting surface thereof, wherein at least one of the first and second jaws is movable relative to the other between open and closed positions, the second jaw having a generally rectangular nominal perimeter opposed to the nominal perimeter of the first jaw; a plurality of attachment features (120, 126) formed on at least one jaw of the first and second jaws on extension elements (118, 122) extending beyond the nominal perimeter of the at least one jaw such that each of the extension elements has at least one attachment feature formed thereon; and an adjunct material having a shape complementary to at least one of the first and second jaws and being configured to releasably mate with the attachment features, wherein the adjunct material comprises at least one mating feature that is complementary to at least one of the plurality of attachment features and is configured to releasably mate with the at least one attachment feature; and wherein the extension elements are formed integrally with the at least one jaw, and wherein the at least one of the plurality of attachment features comprises a projection extending perpendicular to a longitudinal axis of the at least one jaw from the corresponding extension element formed on the at least one jaw, and wherein the at least one mating feature comprises a through opening formed in the adjunct material and configured to receive the projection therein.