A redescription of Podosporites parvus (Couper) Mildenhall emend. Mildenhall & Byrami from the Early Pleistocene, and late extinction of plant taxa in northern New Zealand

Abstract

Numerous specimens of the conifer pollen grain Podosporites parvus, recorded at c. 1.32 Ma in the Pliocene‐Pleistocene Puketoka Formation, suggest that the parent plants inhabited the fringes of lowland, coastal hardwood/podocarp forest. This pollen type has a botanical affinity with Microcachrys and Microstrobos (Podocarpaceae), which are prostrate to small shrubs currently inhabiting alpine and sub‐alpine rocky outcrops, especially in wet areas, and around mountain tarns in Australia. The deposition site also features pollen of Nothofagus (Fuscospora), Dacrydium cupressinum, and several other tall trees, but is dominated by Nestegis. It also contains two extinct mesothermal taxa. The presence of a member of the Australian alpine conifer Microcachrys/Microstrobos group in an Early Pleistocene lowland pollen record from northern New Zealand suggests that such prostrate to small shrub‐like conifers may have occupied different geographic and ecological ranges then than they do today. Moreover, it indicates that the vegetation assemblages have no modern New Zealand equivalent. P. parvus is re‐described and diagnosis emended to highlight its distinctive irregular sacci and granulate‐rugulate cappa, characteristics that distinguish it from other trisaccate grains attributed to Podosporites. The discovery of numerous pollen grains of an extinct species in these Early Pleistocene sediments is additional evidence that northern North Island was the last refuge for many New Zealand plants as they dwindled into extinction with the onset of cooler conditions.