Laurus macrocarpa Lesquereux from the mid-Cretaceous (Cenomanian) Dakota Formation, USA, is a chlamydospermous seed, not an angiosperm fruit

The fossil seed, Decaturospermum macrocarpum (Lesquereux) gen. nov. et comb. nov., is described based on specimens of latest Albian to mid-Cenomanian age (mid-Cretaceous) from the Dakota Formation of Nebraska, and Kansas, USA, which were previously named Laurus macrocarpa Lesquereux; and from the Woodbine Formation of Texas, USA, which were previously named Laurocarpum tetragonale MacNeal. All specimens are molds and casts lacking cellular details, but light microscopy and micro-CT scanning reveal key structural features. Combined information from eight specimens indicates that D. macrocarpum is a seed with an outer covering comprised of four valves. The four valves are reflected in the cast of the seed cavity, which has a quadrangular transverse section with four rounded edges. Each valve has a smooth outer surface covering a decay-susceptible outer layer that was replaced by sediment early during fossilization. Sediment filling the space left by the decaysusceptible outer layer preserves an impression of a distinctive dendritic reticulate system of longitudinal and transverse ribs on its inner surface, which reflects the outer surface of a decay-resistant inner layer, now seen only as a cavity. The inner surface of the decay-resistant inner layer is smooth, as is the outer surface of the cast filling the seed cavity. Below the seed cavity a downward extension of the decay-resistant layer forms a prominent swollen-cylindrical flange around the seed base. Decay-susceptible tissues inside the swollen flange are replaced by sediment but preserve the distinctive sinuous course of four vascular bundles. The position of each bundle suggests that it entered a valve in a near median position. Comparison of Decaturospermum macrocarpum with other seeds of Cretaceous age indicates that the two-layered, four-valved outer covering is the envelope of a chlamydospermous seed, which was most likely produced by plants closely related to extant Gnetales.