Tuesday 5 April 2022

Covidifructus multicarpellatus: A multicarpellate fruit from the Late Cretaceous of South Bohemia.

The earliest Flowering Plants are thought likely to have produced flowers with several carpels (ovule-bearing female reproductive organs) free from each other, a state still seen in Plants such as Lotuses and Roses. However, most modern Flowering Plants have flowers with several fused carpels, typically three in Monocotylodons and two to five in Eudicotids. This is thought to have been a key adaptation in Flowering Plants, allowing more efficient pollination and seed/fruit dispersal, which arose multiple times in different lineages early in the history of the Flowering Plants. Although most modern (and fossil) Flowering Plants have fused carpels, plants with more than five carpels in a single whorl are rare, despite having evolved numerous times in different Plant groups, suggesting the advantages of such an arrangement are limited. Today this condition can be seen in some Water Lilies, Water Plantains, Poppies, and several other lineages. Examples are known in the fossil record as well, including Monetianthus mirus, a Water Lily from the Early Cretaceous of Portugal, Carpestella lacunata, probably a member of an extinct group closely related to Water Lilies, from the Early Cretaceous of North America, and Elsemaria kokubunii, probably a member of the Dilleniaceae, a group of woody shrubs with a largely tropical distribution, from the Late Cretaceous of Japan.

In a paper published in the journal Palaeontologica Electronica on 14 January 2022, Zuzana Heřmanová of the National Museum in Prague, Jana Čepičková of the Institute of Geology and Palaeontology at Charles University, Jiří Kvaček, also of the National Museum in Prague, and Maria von Balthazar and Jürg Schönenberger of the Department of Botany and Biodiversity Research at the University of Vienna, describe a new multicarpellate fruit from the Late Cretaceous of South Bohemia.

The specimen comes from the Klikov Formation (Late Turonian–Santonian) at the Zliv-Řídká Blana Quarry, a typical Laurasian Late Cretaceous site which has produced fossils of Plant reproductive organs, leaves, and wood belonging to the Normapolles (an extinct group related to Oaks and Beeches), Proteales (Proteas), Laurales (Laurels), Ericales (Heathers), as well as Insects and the coprolites of larger Animals. It is a charcoalified and 3-dimensionally preserved specimen representing a 10-carpellate syncarpous gynoecium.

The new species is named Covidifructus multicarpellatus, where 'Covidifructus' refers to the Covid-19 pandemic, which provided the authors with the time to work on the project, and 'multicarpellatus' refers to the multicarpellate nature of the specimen. The specimen has 10 carpels in radial symmetry, each of which has a single locule (cavity) holding a large oblong ovule or seed. Lines of dehiscence (i.e. lines along which the body would be expected to split open) are located on the median-dorsal side of each carpel.

Covidifructus multicarpellatus; specimen No. NMP F3200; scale bars equal 100 μm in all figures. (A) Small premature capsular fruit in lateral view, semi-globose in overall shape; SEM. (B) Fruit seen in apical view; note preformed dorsal lines of fruit dehiscence; SEM. (C) Close-up of fruit apex showing styles and stigmatic areas (asterisks); note irregular closure of ovary in the very centre; SEM. (D) MicroCT volume rendering, lateral view, showing 10 elongate seeds (green), one seed per carpel. (E) MicroCT volume rendering, apical view, showing regular arrangement of carpels and seeds. (F) Detail of central ovary closure (dashed line); note that some of the carpel flanks (arrowheads) do not extend to the very centre of the closure zone; SEM. Heřmanová et al. (2022).

Heřmanová et al. compared Covidifructus multicarpellatus to a range of extant and fossil multicarpellate fruit-bearing Plants. It does not appear to be closely related to either Monetianthus mirus or Carpestella lacunata. It does appear to resemble illustrations of Elsemaria kokubunii somewhat, although Heřmanová et al. disagree with the original description of this fossil, a single permineralized fruit from the Late Cretaceous of Japan, given by Harufumi Nishida in 1994. If Heřmanová et al.'s interpretation of that fossil is correct, then Covidifructus multicarpellatus and Elsemaria kokubuniii are likely to be related, and both to be members of the Dilleniaceae, but re-examination of the original material of Elsemaria kokubuniii would be needed before this can be confirmed.

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