Bamboos and the related rice have an improved C3 efficiency. This improvement might be due to its ability to recapture CO produced during photorespiration, a behavior termed "carbon refixation". These plants achieve refixation by growing chloroplast extensions called "stromules" around the stroma in mesophyll cells, so that any photorespired CO from the mitochondria has to pass through the RuBisCO-filled chloroplast.
Refixation is also performed by a wide variety of plants. The common approach involving growing a bigger bundle sheath leads down to C2 photosynthesis.