Shijun Wang

Noeggerathiales are enigmatic plants that existed during Carboniferous and Permian times, ∼323 to 252 Mya. Although their morphology, diversity, and distribution are well known, their systematic affinity remained enigmatic because their anatomy was unknown. Here, we report from a 298-My-old volcanic ash deposit, an in situ, complete, anatomically preserved noeggerathialean. The plant resolves the group’s affinity and places it in a key evolutionary position within the seed plant sister group. Paratingia wuhaia sp. nov. is a small tree producing gymnospermous wood with a crown of pinnate, compound megaphyllous leaves and fertile shoots each with Ω-shaped vascular bundles. The heterosporous (containing both microspores and megaspores), bisporangiate fertile shoots appear cylindrical and cone-like, but their bilateral vasculature demonstrates that they are complex, three-dimensional sporophylls, representing leaf homologs that are unique to Noeggerathiales. The combination of heterospory and gymnospermous wood confirms that Paratingia, and thus the Noeggerathiales, are progymnosperms. Progymnosperms constitute the seed plant stem group, and Paratingia extends their range 60 My, to the end of the Permian. Cladistic analysis resolves the position of the Noeggerathiales as the most derived members of a heterosporous progymnosperm clade that are the seed plant sister group, altering our understanding of the relationships within the seed plant stem lineage and the transition from pteridophytic spore-based reproduction to the seed. Permian Noeggerathiales show that the heterosporous progymnosperm sister group to seed plants diversified alongside the primary radiation of seed plants for ∼110 My, independently evolving sophisticated cone-like fertile organs from modified leaves. Significance There were two heterosporous lignophyte lineages of which only one, the seed plants, survived the Permian–Triassic mass extinction. Based on exceptionally complete fossil trees from a 300-My-old volcanic ash, the enigmatic Noeggerathiales are now recognized as belonging to the other lineage. They diversified alongside the primary seed plant radiation and constitute seed plants’ closest relatives. Noeggerathiales are reconstructed as members of a plexus of free-sporing woody plants called progymnosperms, extending their age range by 60 My. Following the origin of seed plants, progymnosperms were previously thought to have become gradually less abundant before dying out in Carboniferous. We show they diversified and evolved complex morphologies including cone-like structures from modified leaves before going extinct at the Permian–Triassic extinction.

A new species of permineralized ovule is reported from a previously undocumented diverse fossil plant assemblage preserved in volcaniclastic tuff from the Late Permian Xuanwei Formation at the Huopu coal mine in Guizhou Province, China. The ovule is large and platyspermic, with 180° rotational symmetry. It has a pronounced commissure that distally divides the integument into two valves. The integument comprises a two‐part sarcotesta, a sclerotesta also divided into two parts, and an endotesta that is unusually thick in the central part of the ovule and at the apex. Fusion of the nucellus to the integument occurs only at the chalaza, and the nucellar apex is small, consisting of a proximal pollen chamber and a distally extending tubular projection. A single vascular bundle enters the base of the ovule and divides in the major plane at the boundary of the inner and outer sarcotesta to form two integumentary bundles, one to each side of the ovule, with the nucellar bundle continuing to the base of the nucellus, where it forms a small vascular cup. The gross morphology and the pattern of vascularization of the ovule fit the circumscription of the morphogenus Cardiocarpus Brongniart, to which the ovule is here assigned, but are distinct from previously recognized morphospecies leading to the erection of Cardiocarpus huopuensis sp. nov. In C. huopuensis sp. nov., tissues of the outer sarcotesta are rarely preserved and where present occur external to a zone of poorly preserved cells that suggests exfoliation of the outer sarcotesta through ontogeny. Although the identity and, hence, affinity of the parent plant for C. huopuensis sp. nov. are unknown, previous evidence shows ovules of this kind to be produced by either a coniferophyte or a seed fern (pteridosperm).

A new species of the arborescent lycopsid disseminule Achlamydocarpon is described and diagnosed from volcaniclastic tuffs in the Lower Permian Taiyuan Formation of northern China. Achlamydocarpon pingquanensis sp. nov. comprises a large megasporangium‐sporophyll unit with a dorsiventrally flattened sporangium lacking a dorsal ridge and keel, containing a single functional and three abortive megaspores, each with a conspicuous massa. The pedicel has narrowly winged lateral laminae that develop upward and outward, partially enveloping the basal part of the sporangium. An elliptical xylem strand is developed distally and is surrounded by a parichnos cavity. The sporangial wall has an outer parenchymatous layer, a middle sclerotic layer, and an inner, thick, parenchymatous layer and has a subarchesporial pad with a toothed margin. Achlamydocarpon pingquanensis does not readily conform to the previously recognized distinction between the Achlamydocarpon varius and Achlamydocarpon takhtajanii types, possessing characters belonging to both groups. This adds to a growing body of data on arborescent lycopsids from the Paleozoic Cathaysian floras and supports the systematic distinction of Cathaysian lepidodendralean plants (previously termed “Oriental lepidophytes”) as a distinct subset of the Lepidodendrales. However, their phylogenetic position remains uncertain because of an absence of reconstructed whole plants to enter into cladistic analyses, and thus their crown‐ or stem‐group position within Lepidodendrales is unknown.