Archangelskyoxylon carlquistii gen. et sp. nov. Taxonomy and phylogeny of an unequivocal gnetoid Jurassic fossil wood from Argentina

Abstract

Archangelskyoxylon carlquistii gen. et sp. nov. is based on anatomical secondary xylem from the Lower Jurassic (Sinemurian–Toarcian) in the Roca Blanca Formation of Santa Cruz Province, Patagonia, Argentina. The woods are preserved as siliceous permineralization and examined by light and scanning electron microscopy. The new fossil wood shows a set of anatomical features of the secondary xylem (e.g., vessels with simple, scalariform, foraminate, and modified foraminate perforation plates; vessel with bordered pits with outer aperture vestured or non-vestured, and inner aperture vestured; tracheids with bordered pits; septate fiber-tracheids, and uni to biseriate parenchyma rays), that are related to the Gnetidae and closely resembles those of Gnetum. The new taxon was compared with existing Gnetidae species and included in a phylogenetic analysis to test its relationships with fossil and extant genera of Gnetidae. In the resulting phylogenetic hypothesis, Archangelskyoxylon is placed into a clade that is closely related to Weltwitschia and Gnetum. This finding supports the existence of this lineage in the south of Gondwana during the Jurassic and reinforces the hypothesis that lineages related to the Gnetaceae diverged earlier in South America.