Rhexoxylon brunoi Artabe, Brea et Zamuner, sp. nov., a new Triassic corystosperm from the Paramillo de Uspallata, Mendoza, Argentina
ARTABE, A.E.; BREA, M.; ZAMUNER, A.E.
REVIEW OF PALAEOBOTANY AND PALYNOLOGY
ELSEVIER SCIENCE BV
Lugar: Amsterdam; Año: 1999 vol. 105 p. 63 - 74
A new species of Rhexoxylon from the Upper Triassic of Argentina is described. The material was collected at El Paramillo de Uspallata area and comes from Los Colorados Formation. There is a big buried specimen and scattered material which is preserved by silicification, corresponding to an adult eccentric, oval trunk, whose diameter is 71 x 58 cm. Three zones can be distinguished: pith, vascular (with perimedullar bundles and centrifugal wedges of secondary xylem) and cork layer. Rhexoxylon brunoi Artabe, Brea et Zamuner, sp. nov. has a heterogeneous pith with parenchyma cells and idioblasts. Perimedullar bundles make up two cycles; the first one is complete constituted by double collateral bundles, facing each other, with secondary growth. The second one is incomplete, showing just the centripetal xylem sector. Peripheral centrifugal secondary xylem wedges show extensive development, reaching up to 38 cm of thickness. The tracheids of secondary xylem have opposite uni- to biseriate bordered radial pitting, and crossfields with one or two simple, slanted lenticular pits. Outside of the xylem a cork layer of about 2 cm persists conforming a longitudinally and transversely fractured rhytidome-like zone. Rhexoxylon brunoi shows a morpho-structural pattern determined by high activity of normal cambium, moderate activity of supernumerary cambium and scarce activity of remanent cambium.