A New Iridopteridalean from the Devonian of Venezuela

Abstract

The first permineralized Devonian plant fossil is reported here from the Middle or lowermost Upper Devonian of western Venezuela. Two orders of branching plus dichotomous ultimate appendages are known from compressions. A branch of the first order contains a mesarch actinostele with six primary xylem ribs, each with a protoxylem strand near the rib tip (peripheral edge). Compressions of first‐order branches demonstrate three equally spaced lateral organs (higher‐order branches and dichotomous ultimate appendages) attached in whorls, with every other whorl displaying laterals placed in identical orientations and intermediate whorls with laterals offset exactly halfway between. The permineralized specimen partly confirms the presence of whorls and indicates that vascular traces are derived from every other primary xylem rib in each whorl, with intervening ribs producing traces in whorls above and below. Second‐order branches have only ultimate appendages that are attached in a nonwhorled, three‐dimensional, or alternate arrangement. Sterile ultimate appendages dichotomize up to six times and terminate in recurved 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 plants, resembling Arachnoxylon kopfii Read in arrangement and number of xylem ribs although it is smaller in size. Among iridopteridaleans, the branching pattern and mode of trace departure is unique, and we therefore name the plant Compsocradus laevigatus gen. et sp. nov.