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Percentage green leaf and height of the major perennial grass species was estimated fortnightly at six locations along a rainfall predictability gradient from Katherine (most predictable) to Lake Mere near Cobar (aseasonal), and regressed on estimated plant available soil moisture (PASM) and time of year (T). Green leaf is more strongly related to T at Katherine and to PASM at Lake Mere with the other sites in-between. Differences between species in terms of seasonal growth phenology were minor, at all sites, and there were no meaningful patterns in percentage contributions by the species to sward biomass. A strong inter-seasonal rainfall pattern over the period of the study may have masked phenological differences between species, but it is also possible that changes in species composition very soon after livestock were introduced resulted in a decline in phenological differentiation. Whatever the reason, the differences observed in this study would ~ot warrant their use in the formulation of management strategies.