Physiology and anatomy of medullosan foliage from the Late Carboniferous Illinois Basin, U.S.A.

Plant physiology often yielded important insights on the biomechanical functions of plants and plant-environment interactions through time. This paper investigated the physiology and anatomy of a group of extinct, Late Carboniferous pteridosperms, the medullosans. The aim was to examine how patterns of variation in leaf venation within medullosan foliage, as quantified by leaf vein density, might inform about the physiology of medullosans and interactions between medullosans and the external environment. In contrast to stomatal and stem hydraulic conductivity, previously known to be high, the leaf vein density of medullosans from the Illinois Coal Basin, U.S.A. was within a fairly low range between 1-3 mm leaf vein/mm2 leaf area across 5.5 million years. Low leaf vein density with high hydraulic conductivity suggested leaf adaptations to meet evapotranspiration demands. The stability of leaf vein density observed suggested that leaf vein density alone couldn’t serve as a paleoenvironmental proxy, highlighting the importance of whole-plant functional modeling