Middle Triassic megafossil marine algae and land plants from near Benmore Dam, southern Canterbury, New Zealand

The upper Blackjacks Conglomerate, near Benmore Dam, contains megafossil plants very similar to Ladinian (Kaihikuan local stage) fossil plants in Long Gully, only 5 km to the southwest, and in Tank Gully, Canterbury. A greater variety of fossil plant associations has been discovered near Benmore Dam than in these other two areas of New Zealand, and these allow improved understanding of Triassic coastal vegetation of the Gondwana supercontinent. Abundant fossil codiacean algae, Shonabellia verrucosa gen. et sp. nov., at one locality, are evidence that these were near‐marine and coastal floras. Shonabellia is intermediate in several features between well‐known Ordovician fossils of Palaeoporella and the modern seaweed Codium . It provides evidence that these unsegmented and weakly‐calcified codiacean algae may have evolved independently of segmented, calcareous codiaceans since the early Palaeozoic. Seed fern leaves of Pachydermophyllum were found in an almost monodominant association nearest the locality for marine algae and probably formed mangal vegetation along inland reaches of estuaries. At least two species ( P. dubium and P. praecordillerae ) are present, along with some distinctive un‐named fragments which have crenate margins and bundled, secondary veins. Other forms identified are usual for Middle Triassic megafossil floras, and include leaf remains of Todites (sterile and fertile), Cladophlebis, Dicroidium, Taeniopteris, Ginkgophytopsis and Linguifolium , and fossil fructifications of Peltaspermum, Pilophorosperma, Pteruchus and Carpolithus . Leaves of the seed fern Lepidopteris madagascariensis , and of the problematical Ginkgophytopsis cuneata and G. tasmanica , are here recorded for the first time from New Zealand.