Sporophytes of polysporangiate land plants from the early Silurian period may have been photosynthetically autonomous

Abstract

The colonization of land by vascular plants is an extremely important phase in Earth's life history. This key evolutionary process is thought to have begun during the Middle Cambrian period and culminated in the Silurian/Early Devonian period (interval about 509-393 million years ago (Ma)), and is documented primarily by microfossils (that is, by dispersed spores, phytodebris including fragments of algae, tissues, sporangia and cuticles), tubes and rare megafossils . A newly recognized fossil cooksonioid plant with in situ spores from the Barrandian area, Czech Republic, is of the highest importance because it represents extremely ancient megafossil evidence of land plant diploid generation: sporophytes (~432 Ma). The robust size of this plant places it among the largest known early polysporangiate land plants and it is probable that it attained adequate size for both aeration and effective photosynthetic competence. This would mean not only that sporophytes were photosynthetically autonomous but also that the they might have been able to sustain a relatively gametophyte-independent existence.

An alternative model for the earliest evolution of vascular plants

“…), and the earliest vascular plant evidence, which corresponds to mid‐Silurian Cooksonia macroremains (Libertín et al . ). This gap could still be larger if we consider the recently suggested Morris et al .…”

Plant Diversity of The Mid Silurian (Lower Wenlock, Sheinwoodian) Terrestrial Vegetation Preserved in Marine Sediments from The Barrandian Area, The Czech Republic

“…R e m a r k s . For diagnosis, description, and spores in situ see Libertín et al (2018). However, some details, particularly related to the handwritten notes, were not mentioned in the paper referred to above.…”

“…Early land plants found in the Silurian marine sediments of the Barrandian area of central Bohemia (the Czech Republic) have been a recent focus of Czech palaeobotanists (Kraft and Kvaček 2017, Kraft et al 2018, Libertín et al 2018. The latter publication is of particular importance because it documents Cooksonia barrandei LIBERTÍN, J.KVAČEK, BEK, ŽÁRSKÝ et ŠTORCH in sediments dated to about 432 Myr, making it the earliest megafossil polysporangiate land plant (Libertín et al 2018). It is of particular interest that the next oldest evidence of polysporangiate land plants comes from sediments approximately 5 Myr younger (Homerian Stage) in Ireland (Edwards et al 1983).…”

“…Taylor et al 2009), and they are characterized by very small size. This particular feature led Boyce (2008) to hypothesize that their life cycle was similar to that of modern bryophytes, however this was questioned by Libertín et al (2018), who used large size of C. barrandei as one of the major counter-arguments.…”

Baltica cradle of early land plants? Oldest record of trilete spores and diverse cryptospore assemblages; evidence from Ordovician successions of Sweden

“…The oldest unequivocal megafossil of terrestrial sporophytes, i.e. early land plants is Cooksonia barrandei found in Silurian (middle Sheinwoodian) deposits in the Czech Republic (Libertín et al 2018). However, the recent discovery of putative plant remains from the Hirnantian of Poland (SW peri-Baltica), are most likely the earliest record of vascular land plants (polysporangiophytes) dated to the Late Ordovician (Salamon et al 2018).…”