The anatomical characters of Ephedra tweediana secondary xylem CA Meyer are described, provided photomicrographs and quantitative data of its structure. The observed details correspond to those described in the literature for other species of the genus. The anatomy of the wood stands out for the presence of true vessels and very high rays, up to 8 cells wide. These aspects are common in dicotyledonous angiosperms but absent in gymnosperms, with the exception of 3 genera of Chlamydospermae or Gnetales . Within this group, Ephedra is distinguished by having foraminated or ephedroid perforation plates. For the South-Brazilian species, the presence of very short tracheids, dotted in a uniseriate arrangement and the peculiar contour of the "stepped" growth rings are also worthy of mention
