Pollen cones and associated leaves from the Lower Cretaceous of China and a re-evaluation of Mesozoic male cycad cones

Abstract

Male cones of Ixostrobus hailarensis from Lower Cretaceous strata of the Hailar region of north-east China were re-examined for features of their cuticle and in situ pollen. The cones are loosely aggregated and possess helically arranged peltate microsporophylls containing resin bodies. Microsporophyll cuticle is thick, papillate and has elliptical stomata with 6–9 subsidiary and ∼10 encircling cells. Adaxial sporangia contain monosulcate pollen assignable to the dispersed taxon Cycadopites minimus. Both the cuticle and pollen are distinct from Ixostrobus but are consistent with the cycad genera Androstrobus, Aegianthus, Loricanthus and the putative angiosperm Solaranthus. Reanalysis of the type species of Androstrobus, A. zamioides, provides new information on its structure and allows an accurate delimitation of the genus and improved comparison with other genera. A new genus, Schimperstrobus, is erected for species now excluded from Androstrobus. Comparisons indicate that Solaranthus represents a male cycad cone and that Aegianthus, Loricanthus and Solaranthus are synonyms; Aegianthus has nomenclatural priority. We emend the combined generic and specific diagnoses for Aegianthus sibiricus to allow additional species to be placed in the genus, and erect the new combinations Aegianthus resinifera for specimens previously assigned to Loricanthus, and Aegianthus daohugouensis for specimens previously placed within Solaranthus. The Hailar cone conforms to the generic circumscription of Aegianthus and represents a new species that we name A. hailarensis comb. nov. Androstrobus phialophora also conforms with Aegianthus and is transferred to Aegianthus phialophora comb. nov. Co-occurring with A. hailarensis are cuticles of the ginkgophyte leaf Sphenobaiera longifolia that are similar to microsporophyll cuticles of A. hailarensis. However, we discount that they belong to a single plant species and conclude that the cuticles of some Mesozoic ginkgoalean and cycadalean taxa may be virtually indistinguishable. We consider that Aegianthus was widespread across China, Mongolia and southern Russia during the Upper Jurassic to Lower Cretaceous.