Malvaceous wood from the Late Pleistocene El Palmar Formation of northeastern Argentina

We describe a new species of Bastardiopsis, Bastardiopsis palaeodensiflora sp. nov., which is the first fossil Malvaceae wood reported in Argentina. It was collected from the Arroyo Yuquerí of El Palmar Formation, a late Quaternary fluvial unit, located in the middle Uruguay River Basin, NE Argentina. The diagnostic features of this fossil wood are growth ring boundaries demarcated by marginal parenchyma; diffuse porous wood; vessels solitary and in radial multiples of 2-3 elements; alternate and minute-to-small sized intervessel pits; tyloses abundant; vessel-ray parenchyma pits similar in size and shape to intervessel pits; vasicentric, and diffuse axial parenchyma; rays of two distinct sizes, mostly 4-5 cells wide; prismatic crystals in upright and/or square marginal cells, sheath cells, non-septate fibres, rays and vessel elements irregularly storied. These features suggest an assignation to Bastardiopsis (K. Schumann) Hassler, a genus with five extant species, extending from the north of South America to northern Argentina, mainly distributed in tropical to temperate areas. The eco-anatomical features, the Nearest Living Relatives (NLRs), the Vulnerability Index, the Mesomorphy ratios and the Taxon Independent Approach (TIA) indicate that this fossil grew under temperate-warm and humid conditions. This is consistent with other proxies (geological, sedimentological and microfossil data) suggesting a similar environment for this region during some periods of the Late Pleistocene.