New Iridopteridalean from the Devonian of Venezuela

The first permineralized Devonian plant fossil is reported here from the Mi ddle or lowermost Upper Devonian of western Venezuela. Two orders of branch ing plus dichotomous ultimate appendages are known from compressions. A bra nch of the first order contains a mesarch actinostele with six primary xyle m ribs, each with a protoxylem strand near the rib tip (peripheral edge). C ompressions of first-order branches demonstrate three equally spaced latera l organs (higher-order branches and dichotomous ultimate appendages) attach ed in whorls, with every other whorl displaying laterals placed in identica l orientations and intermediate whorls with laterals offset exactly halfway between. The permineralized specimen partly confirms the presence of whorl s and indicates that vascular traces are derived from every other primary x ylem rib in each whorl, with intervening ribs producing traces in whorls ab ove and below. Second-order branches have only ultimate appendages that are attached in a nonwhorled, three-dimensional, or alternate arrangement. Ste rile ultimate appendages dichotomize up to six times and terminate in recur ved tips. Fertile ultimate appendages have paired sporangia distally; these sporangia are often upright but are otherwise similar to sterile examples. The stelar anatomy demonstrates an iridopteridalean affinity for these pla nts, resembling Arachnoxylon kopfii Read in arrangement and number of xylem ribs although it is smaller in size. Among iridopteridaleans, the branchin g pattern and mode of trace departure is unique, and we therefore name the plant Compsocradus laevigatus gen. et sp. nov.