A new morphospecies of palm trunk, Palmoxylon pichaihuensis sp. nov., is proposed on the basis of several specimens recovered from a succession of tuffs and breccias at Pichaihue, Neuquén Province, Argentina. The specimens comprise atactosteles that display densely crowded fibrovascular bundles in the peripheral zone, and less congested fibrovascular bundles, randomly scattered or arranged in irregular circles in the central zone; sclerenchyma reniform; xylem with 1-4 large metaxylem vessels and 6-12 smaller protoxylem elements in the central zone, and an f/v ratio of 1.3-2:1. The Pichaihue fossil assemblage is similar to, and probably coeval with the flora of Bajo de Santa Rosa, Río Negro Province, reflecting a warm and relatively humid climate, at ca. 40- 45º S, in southern South America during the Late Cretaceous.