C4 Grasses: an Anatomical Criterion for Distinguishing Between NADP-Malic Enzyme Species and PCK or NAD-Malic Enzyme Species

Transections of leaf blades from 46 C4 grass species of known C4 type were recorded for presence (XyMS+) or absence (XyMS-) of cells intervening between metaxylem vessel elements and laterally adjacent chlorenchymatous bundle sheath cells of primary lateral vascular bundles. A perfect correlation, only 'NADP-ME type' species being XyMS-, indicated that XyMS type serves as a useful predictor of C4 species type. The likely C4 type of 255 biochemically-untyped grass species was accordingly deduced by direct observation (94 spp.) or from Metcalf's anatomical descriptions (161 spp.). All 124 C4 species examined, including C3 eu-panicoids, proved to be XyMS+.