Use of environmental water allocations to conserve floodplain and wetland plants is becoming an increasingly common management tool. In south-eastern Australia, Pseudoraphis spinescens (R.Br.) Vickery has historically covered extensive areas within Barmah Forest where it is deemed to be ecologically significant and of high conservation value. The areal extent of P. spinescens significantly declined throughout the forest during the Millennium drought (1996–2010). Natural flooding (2010–2012) failed to elicit an expected increase in the extent of P. spinescens, suggesting that this species may not have a viable long-lived seed bank. We investigated the presence and viability of the seed bank of P. spinescens by (1) germination trials, (2) identification of seeds within the sediment and (3) estimates of seed viability. No plants were identified as P. spinescens during the germination trial. Seeds of P. spinescens were identified as present in the sediment, but the majority (98%) were not viable. In contrast, 16% of seeds collected from mature seed heads were found to be viable. The present study demonstrated the absence of a persistent long-lived seed bank of P. spinescens in Barmah Forest.