Varying Photosynthetic Pathway and a C₃-C₄ Intermediate in Australian Neurachne and its Allies (Poaceae)

Abstract

The Australian grass tribe Neurachneae S.T. Blake comprises ten endemic species (Table 1) in three closely-related genera (Neurachne, Paraneurachne, and Thyridolepis: Blake 1972). Using anatomical criteria, Thyridolepis (3 spp.)¹ was inferred to be C₃, and the monotypic Paraneurachne to be C₄, while Neurachne apparently contained both C₃ and C₄ species (Hattersley et al. 1982). δ¹³C value determinations confirm these predictions, with N. munroi (F. Muell.) F. Muell. being C₄, and N. alopecuroidea R. Br., N. lanigera S.T. Blake, N. queenslandica S.T. Blake, and N. tenuifolia S.T. Blake all C₃ (Hattersley, Roksandic 1983). N. minor S.T. Blake, however, exhibits C₃ plant δ¹³C values, although its leaf anatomy (Fig. la) closely resembles that of the C₄ species in the group, being of the rare ‘Alloteropsis-type’ (Hattersley et al. 1982; Hattersley, Roksandic 1983). In P. muelleri (Hackel) S.T. Blake, N. munroi, and N. minor, the cell walls of inner sheaths in all the veins possess a suberized lamella, as do mestome sheath walls in primary veins in the C₃ Neurachneae (P.W. Hattersley, S. Perry, unpublished). The distribution of the suberized lamella in the C₄ species and N. minor is the same as in C₄ NADP-malic enzyme grasses (Hattersley, Browning 1981).