A review of the Early Mississippian anatomically preserved flora from Montagne Noire

In 1870, Schimper documented an anatomically preserved lycopsid cone found near the town of Cabrieres, in the Herault region of France. Since this initial report, over 500 specimens have been collected from Tournaisian (early Mississippian) outcrops in this area. They include permineralized specimens from the radiolarian cherts and associated phosphatic nodules of the Lydiennes Formation, and a hundred compressions in argilites, some with cellular preservation. Here we provide an updated review focused on the plants from the cherts, based on a database of 441 specimens corresponding to stems (66%), leaves/petioles (27%), fertile structures (4%), and roots (1%). Seed plants are by far the most abundant and diverse group of plants and constitute approximately 64% of the specimens assignable to that group. Some genera such as Calamopitys, Stenomyelon, Tristichia, Eristophyton, Lyginorachis, Kalymma and Periastron are also found in other Late Devonian-Mississippian localities. Four genera are only documented to date in the Montagne Noire: Faironia, Lyginopitys, Triichnia, and Coumiasperma, the latter being the only seed known in the chert. Lycopsids, cladoxylopsids, and zygopteridalean ferns each represent about 10% of the specimens. Lycopsids include different types of stems and two species of Flemingites (Lepidostrobus). Cladoxylopsids are represented by stems assignable to a single genus, Cladoxylon. Zygopteridalean ferns include many types of Clepsydropsis petioles/ phyllophores; their diversification is interpreted as evidence of early radiation preceding the emergence of two clades, one leading to the quadriseriate zygopteridaleans and the other to the biseriate ankyropterid/tedeleans. The less abundant groups are the progymnosperms and sphenopsids, each corresponding to 1-2% of the specimens. Sphenopsids are only represented by small stems of Sphenophyllum. The progymnosperms include vegetative and fertile remains assigned to Protopitys, and the putative progymnosperm stem Stauroxylon, which is currently being reinvestigated. The plants from the Montagne Noire constitutes one of the few well-dated middle Tournaisian floral assemblage in the world. As such, they provide key information on plant evolution, especially the diversification of ferns s.l. and seed plants. They also document floral changes between the Devonian and the Carboniferous, with the presence of a mixture of taxa belonging (1) to groups that were abundant and diverse during the Devonian and disappeared during the Carboniferous, such as the cladoxylopsids and progymnosperms, and (2) to groups that appeared in the late Devonian and diversified to become emblematic members of Carboniferous floras, such as the Sphenophyllales, the zygopteridalean and tedelean ferns, and the seed plants.