Study species
Chionochloa pallens (midribbed snow tussock) is an endemic alpine New Zealand perennial, in the Danthonioideae sub-family of the Poaceae (grasses) (Soreng et al., 2015). Plants grow as tussocks (bunchgrasses) around 0.5-1.5 m tall and 15-50 cm in basal diameter. These are very long-lived plants (> 100 years) with discrete individuals. Each individual plant typically comprises hundreds of tillers, each of which in the field is reported to grow for four to five years prior to attaining reproductive maturity (Mark, 1965; Rees et al., 2002). Tillers may then wait some years before switching from vegetative to reproductive, producing a flower stalk (or culm) and typically at least one daughter tiller, before that flowering tiller (but not the rest of the plant) dies. Activation of the inflorescence and floral development in C. pallens occurs a year before flowering (Mark, 1965, and see Appendix S1 in the supplementary information), so we sampled leaves for genetic analysis from marked tillers and stored the samples at -80 °C until the fate of that tiller could be determined up to a year later. Informative samples were then selected for RNA analysis. The levels of flowering in C. pallensvary markedly between years (Kelly et al., 2013; Kelly et al., 2000). Previous studies, including transplant experiments to different altitudes, have shown that flowering in Chionochloa is heavier after warm summer temperatures in the year preceding flowering (Mark, 1965; Kelly et al., 2013).