Jiřina Dašková

A new Late Cretaceous ginkgoalean reproductive structure Nehvizdyella gen. nov. from the Czech Republic and its whole-plant reconstruction

During the Mesozoic Era, gingkoaleans comprised a diverse and widespread group. Here we describe ginkgoalean fossils in their facies context from the Late Cretaceous (Cenomanian) Peruc-Korycany Formation of the Czech Republic and present a reconstruction of tree architecture and ecology. Newly described in this study is the ovuliferous reproductive structure, Nehvizdyella bipartita gen. et sp. nov. (Ginkgoales). This ovuliferous organ consists of a bifurcating axis, terminated by large cupule-like structures, probably homologous to the collar of the recent Ginkgo. Each cupule encloses an orthotropous ovule. In specimens with the early developmental stages preserved, the entire ovule and young seed, with the exception of the micropylar area, is embedded in the cupule. Mature seeds consist of sclerotesta and sarcotesta. Monosulcate pollen grains of Cycadopites-type are found adhering to the seeds. Although similar to Ginkgo in terms of its large size and reduced number of seeds, N. bipartita differs from the extant genus in having ovules completely enclosed in a cupule-like structure. The co-occurrence of N. bipartita with ginkgoalean leaves of Eretmophyllum obtusum (Velenovský) Kvaček, J., ginkgoalean short shoots of Pecinovicladus kvacekii Falcon-Lang, and ginkgoalean trunk wood of Ginkgoxylon gruettii Pons and Vozenin-Serra in monodominant taphocoenoses at four geographically distant localities suggests that these remains all belong to one plant. This is supported by the close morphological and anatomical similarity between the different organs. Facies analysis of plant assemblages indicates that our Cretaceous tree occupied a water-stressed coastal salt marsh environment. It therefore represents the first unequivocal halophyte among the Ginkgoales.

Composition and structure of an in situ Middle Pennsylvanian peat-forming plant assemblage buried in volcanic ash, Radnice Basin (Czech Republic)

Abstract A three-dimensional reconstruction is provided of the composition, spatial distribution, and structure of a single-aged, Middle Pennsylvanian (Moscovian) peat-forming forest of a high-ash, planar (rheotrophic) mire, buried in situ by volcanic ash and preserved in the Lower Radnice Coal of the Radnice Basin (Czech Republic). The reconstruction is based on a detailed taxonomic and taphonomic analysis of fossils in a ∼0.5-m-thick tuff bed at the base of the Whetstone Horizon excavated over an area of 93.5 m2. In all, 24 whole-plant taxa of various growth forms were identified. This assemblage represents a lepidodendrid- and Cordaites borassifolius-dominated forest, with a well-developed understory of subarborescent lycopsids, tree ferns, medullosan pteridosperms, and calamites, as well as herbaceous ground cover. Lycopsids were dominated by Lepidodendron simile bearing Flemingites-type cones and L. lycopodioides; Lepidophloios cf. acerosus was subdominant. Lianas, mostly lyginopterid pteridosperms and some ferns, were usually found close to upright stems. The ground cover, mostly ferns and sphenophyllaleans, was taxonomically the most diverse stratum, although only a minor contributor to the peat. Based on samples from the coal roof, the palynological record is in agreement with the tuff bed assemblage except for the quantity of certain taxa. To reduce this bias, compression R-values were calculated from the percent cover of aerial plant parts in the excavation and in the dispersed palynoflora. These R-values suggest that in the palynological record, arborescent lycopsids and sphenophylls are greatly overrepresented, ferns and cordaites strongly underrepresented, and calamites are almost the same in both records.

A re-examination of Cenozoic Polypodium in North America

Abstract The sterile holotype of Polypodium fertile MacGinitie was re-examined together with other fertile type specimens from the Miocene Weaverville Formation at Redding Creek (California, western USA). In its leaf morphology, venation and in situ spores Polypodium fertile matches the extant Polypodium vulgare complex. The spores belong to the verrucose type I (sensu Lloyd). In view of discrepancies between the original description and the real morphology of the sterile frond of ‘Polypodium’ alternatum Pabst from the Chuckanut Formation of northwestern Washington (Eocene), this fern must be excluded from the record of Polypodium.