The effect of pyrite on the tracheid structure of Drepanophycus spinaeformis, a long-ranging devonian lycopod

Abstract

The anatomy of Drepanophycus spinaeformis has not been well known because the plant is usually found as a compression fossil. Tracheids of this long-ranging lycopod have occasionally been reported and have been found to have an unusual reticulate wall layer. In this paper the specimens described are coaly compressions with pyritized vascular strands. They yielded additional information on vascular anatomy and on tracheid structure. The xylem is a shallowly lobed protostele, and small cells, probably representing protoxylem, can be seen at the tips of the lobes. All tracheids bear annular and/or helical thickenings. Macerated tracheids, as seen in transmitted light, have a perforated sheet or reticulum between the secondary wall thickenings. Observations with SEM reveal that the organic reticula underlie the secondary wall layer and represent the remains of the compound middle lamella. The crystallization of the pyrite matrix appears to have been responsible for the perforation of what was once a continuous wall layer. There seems to be no taxonomic or phylogenetic significance to the organic reticula. The specimens are from three localities and ages: (1) Battery Point Formation, north shore of Gaspé Bay, Que., probably Late Emsian (Early Devonian); (2) Panther Mountain Formation, west flank of Brown Mountain, Gilboa, N.Y., Givetian (Middle Devonian); (3) Oneonta Formation, west slope of Cave Mountain, Prattsville, N.Y., Early Fransnian (Late Devonian). The plants were identified as Drepanophycus spinaeformis on the basis of morphology and cuticular patterns.