Well preserved secondary phloem was found in a trunk-sized axis (Callixylon trifilievii/henkei-type) and a small branch (C. trifilievii/zalesskyi-type) of Archaeopteris from Late Devonian beds of Morocco and New York (early Famennian marine beds near Jebel El Mrakib, Morocco, and basal Frasnian Oneonta Fm. from Ashland, NY). Previous reports of bark in Callixylon (Arnold 1929, 1930; Lemoigne, Iurina, and Snigirevskaya 1983) did not clearly identify secondary phloem so that the existence of this tissue in Archaeopteris was uncertain, but described as simple. Our new material shows unequivocally that Archaeopteris has complex secondary phloem and bifacial vascular cambium (VC) similar to those of aneurophytes where these tissues are better known. The small (1.5 cm diam) branch has intact VC and a thin layer of secondary phloem. The large (11 cm diam) branch or trunk lacks preserved VC but has a thick zone (7 mm) of secondary phloem with conspicuous rays and concentric tangential bands of fibers and parenchymatous cells. Short radial files of fibers are abundant in the innermost (0.5 mm) youngest phloem. Both axes show that phloem rays have similar widths and heights as xylem rays, have similar but larger procumbent cells, and lack ray tracheids. Clusters of sclereid-like (tanniniferous?) cells and elongate sieve cell-like elements occur amongst the axial parenchyma. Expansion adjustment of older tissues is by enlargement of axial parenchyma cells, preferentially in the radial direction, so that concentric fiber bands are spaced farther apart. Secondary phloem of Archaeopteris is thus histologically similar to that of aneurophytes, differing only by fibers occurring mostly in concentric tangential bands in older external phloem. Bifacial VC of Archaeopteris is also organized like that of aneurophytes. Despite differences of vegetative and reproductive morphology, the similar secondary tissues and VC of Archaeopteris and aneurophytes support interpreting them as closely related basal lignophyte groups.

Key words: Archaeopteris, Devonian, phloem, progymnosperm