Androdecidua endressiigen. et sp. nov., from the Late Cretaceous of Georgia (United States): Further Floral Diversity in Hamamelidoideae (Hamamelidaceae)

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Abstract
The early history of Hamamelidaceae is currently documented by several reproductive structures from Late Cretaceous sediments of the Northern Hemisphere. Recently discovered floral remains from the late Santonian (Late Cretaceous) Allon locality, in central Georgia (United States), represent an additional extinct taxon, Androdecidua endressii gen. et sp. nov., which documents further floral diversity within Hamamelidaceae. The remains of A. endressii comprise the androecium and corolla of a whorled, pentamerous, and actinomorphic flower. Calyx and gynoecium are unknown. The androecium consists of 10 stamens arranged in two alternating whorls of five, with the stamen filaments fused at their bases. The five petals are fusiform and slightly dorsiventrally flattened. They are opposite and basally fused to the filament bases of the inner whorl of stamens. The stamens and petals detach as a unit from the floral receptacle. The stamens have distinct filament and anther and a prominent apical extension of the anther connective. Filaments are massive, broad, and nearly parallel‐sided. Anthers are short and abaxially rounded, but radially elongate. The long apical extension of the connective is flattened and directed toward the center of the flower, where the connective extensions of the 10 stamens converge to form a low conical peak. Stamens of the outer whorl have bithecal and bisporangiate anthers in which the adaxial pollen sac of each theca is missing. Thecal dehiscence is through a single valve. Stamens of the inner whorl have bithecal and tetrasporangiate anthers that dehisce through two valves. Pollen grains are spheroidal and tricolpate, with a coarse and moderately heterobrochate exine reticulum and a line of gemmae on the aperture membrane. The presence of a long apical extension of the connective and the valvate anther dehiscence indicate the affinity of A. endressii with the genera of subtribe Loropetalinae (Hamamelideae; Hamamelidaceae). The level of synorganization of the corolla and androecium and the presence of two structural types of anthers are characters previously unknown among Hamamelidaceae.