The presumed ginkgophyte <i>Umaltolepis</i> has seed-bearing structures resembling those of Peltaspermales and Umkomasiales.

Abstract

The origins of the five groups of living seed plants, including the single relictual species <i>Ginkgo biloba</i>, are poorly understood, in large part because of very imperfect knowledge of extinct seed plant diversity. Here we describe well-preserved material from the Early Cretaceous of Mongolia of the previously enigmatic Mesozoic seed plant reproductive structure <i>Umaltolepis</i>, which has been presumed to be a ginkgophyte. Abundant new material shows that <i>Umaltolepis</i> is a seed-bearing cupule that was borne on a stalk at the tip of a short shoot. Each cupule is umbrella-like with a central column that bears a thick, resinous, four-lobed outer covering, which opens from below. Four, pendulous, winged seeds are attached to the upper part of the column and are enclosed by the cupule. Evidence from morphology, anatomy, and field association suggests that the short shoots bore simple, elongate <i>Pseudotorellia</i> leaves that have similar venation and resin ducts to leaves of living <i>Ginkgo</i><i>Umaltolepis</i> seed-bearing structures are very different from those of <i>Ginkgo</i> but very similar to fossils described previously as <i>Vladimaria. Umaltolepis</i> and <i>Vladimaria</i> do not closely resemble the seed-bearing structures of any living or extinct plant, but are comparable in some respects to those of certain Peltaspermales and Umkomasiales (corystosperms). Vegetative similarities of the <i>Umaltolepis</i> plant to <i>Ginkgo</i>, and reproductive similarities to extinct peltasperms and corystosperms, support previous ideas that <i>Ginkgo</i> may be the last survivor of a once highly diverse group of extinct plants, several of which exhibited various degrees of ovule enclosure.