Organization, anatomy, and fungal endophytes of a Triassic conifer embryo

Abstract

Much is known about the Paleozoic conifers and the conifers assignable to extant families that appear in the Jurassic; however, relatively little is known about the transitional conifers of the early Mesozoic, especially the Voltziales. To better understand the evolution of this group, we aim to increase knowledge of voltzialean anatomy and morphology. A fossil embryo of the group is described in this study. • Several permineralized seeds, one containing a well-preserved embryo, were collected from the early Middle Triassic Fremouw Peak locality in the Central Transantarctic Mountains. Samples were prepared using the standard acetate peel technique and studied in transmitted light. • The embryo belongs to Parasciadopitys aequata, a member of the Voltziales. The embryo and megagametophyte tissues are exquisitely preserved. The embryo is colonized by two distinct fungi. Sporocarps of the fungi are found in the megagametophyte and in the space between the megagametophyte and nucellus. The additions of embryo and megagametophyte characters to the description of P. aequata have made it one of the most completely known fossil taxa reproductively. • Preservation of fossil embryos, although rare, can expand the array of characters available in tracing the evolutionary history of plants. The embryo of P. aequata shares similarities with embryos of other extinct and extant conifer families. The association of the embryo with Combresomyces cornifer and Mycocarpon asterineum increases our understanding of the roles of microorganisms in Triassic ecosystems.