Anatomy and development of fruits of Lauraceae from the Middle Eocene Princeton Chert.

Investigations of the Middle Eocene Princeton Chert reveal evidence for the connection of lauraceous flowers to fruits through a developmental series. Youngest fruits are found with attached floral remnants. Later stages show receptacle enlargement, fruit wall thickening, and the development of abundant sclereid clusters. Mature fruits are borne on a shallow receptacle and have an endocarp palisade layer of radially elongate cells with stellate outlines, an inner mesocarp layer of radiately arranged sclereid clusters, and a fleshy outer mesocarp layer containing numerous idioblasts with contents. Each mature fruit bears a single seed retaining the outer integument with an innermost radially elongate transfusion cell layer. Mature seeds contain a cellular embryo bearing idioblasts. Fruits are distinguishable from previously described anatomically preserved fossil taxa. This study represents the only documented developmental reconstruction of fossil fruits of Lauraceae and that self-pruning evolved prior to the Eocene. Anatomical modifications over the developmental sequence indicate that different stages of maturity preserved together, may be erroneously identified as several taxa at a fossil locality. Fossil morphotypes typically underestimate species number, but this study suggests that the number of inferred species based on fruit types may be inflated for Lauraceae, potentially exaggerating the tropical interpretation of the paleoenvironment.