Eucommiitheca hirsuta, a new pollen organ withEucommiiditespollen from the Early Cretaceous of Portugal

Abstract

A new pollen organ, Eucommiitheca hirsuta, containing Eucommiidites pollen grains is described from the Early Cretaceous of Portugal. The material comprises dispersed microsporangiate units and fragments of axes bearing microsporangiate units in an opposite and decussate arrangement. Each microsporangiate unit consists of a slightly angular to rounded peltate scale attached centrally to a short stalk, and with whorls of sporangia around the distal part of the stalk. Sporangia are stalked and free, with longitudinal dehiscence, and contain pollen grains similar to the characteristic dispersed pollen genus Eucommiidites. Eucommiitheca is comparable to Erdtmanitheca, another Cretaceous pollen organ containing Eucommiidites pollen, in the peltate nature of the microsporangiate units, but microsporangiate units in Erdtmanitheca are arranged in dense heads and sporangia are elongate. The opposite and decussate arrangement of the microsporangiate units in Eucommiitheca is in accordance with the possible affinity to the Gnetales suggested earlier for Eucommiidites-producing plants based on structure of their pollen grains and seeds, but peltate microsporophylls similar to those of Eucommiitheca do not occur in the Gnetales. Eucommiitheca is compared to other fossil reproductive organs, and the bennettitalean affinity of the fossil Sturiella langeri is questioned in light of our new findings. A new family Erdtmanithecaceae is established to accomodate Eucommiidites and the Eucommiidites-producing plants Eucommiitheca, Erdtmanitheca, Erdtmanispermum, Spermatites pettensis, S. patuxensis, and Allicospermum retemirum. This family is based on a unique suite of reproductive characters, including peltate microsporangiate units aggregated in heads or spikes, each bearing numerous sporangia in a radial arrangement; pollen grains with two lateral colpi or a ring colpus flanking a distal main colpus; and seeds with a distinct megaspore membrane, several envelopes surrounding the nucellus, and a long, narrow micropylar tube.