Today, plants constitute more than two-thirds of the global biomass and include over 390,000 different species. However, this present day diversity represents only a small fraction of that which has existed over geological time and paleobotany remains critical to understand both the origin of today’s diversity and how plants have adapted to very different environmental conditions through time.
In this context, the Paleozoic, and especially the Devonian and Carboniferous periods (420 to 300 million years ago), constitute a crucial time to study past plant diversity. From a biological point of view, it sees the colonization of the continents by plants, the rise of the first trees and first forests, and the emergence of complex terrestrial ecosystems. From an environmental point of view, it is marked by major climatic fluctuations and by two first-order extinctions events in the end of the Devonian. The importance and nature of feedbacks between vegetation and climate during these environmental changes is still a subject of debate. One of the major obstacles is our incomplete knowledge of the diversity and biology of plants that were growing at the time, which in turns limits our comprehension of plantenvironment interactions.

The general objective of this PaleoPARADE collaborative project is to provide a better understanding of plants that grew in France and Ireland during the Devonian and Carboniferous. At that time, the two countries were located in the tropical belt. The climate was cooling but the world was still significantly warmer than today, with global temperatures of 24- 20 °C in the late Devonian to early Carboniferous (vs. 14°C today). The movement of continental plates was bringing France and Ireland closer to the equator and changes in precipitation patterns were leading to more humid conditions. To fully understand the vegetation of this paleotropical region and how it reacted to environmental changes it is essential to answer the following questions:
(1) What was plant diversity at the time? For this we need to identify the systematic affinities of the plants and assess how many species were present
(2) How did these plants function? For this we need to reconstruct their biology and understand how they interacted with their environment and with other organisms.

Both France and Ireland have yielded fossil plants of Devonian-Carboniferous age that are permineralized or petrified, a process that leads to the three dimensional preservation of plant tissues and allows the study of very fine details of their anatomy.This exceptional preservation offers a rare chance to observe the minute details necessary to understand the physiology of extinct plants and to study functional traits (e.g., the anatomy and properties of conducting cells). They can also provide evidence of interactions, especially with micro-organisms that can be preserved inside the fossilized plant tissues.

By combining the field localities, fossil collections, and expertise in paleobotany and paleomycology of the French and Irish teams, we will (1) describe new fossil plants, (2) reconstruct important functional traits, and (3) document past plant-fungi interactions. Our
results will be compared with available data on the rare other floras of comparable age that have been reported around the world and replaced in a broader framework to better understand Devonian-Carboniferous vegetation dynamics and paleobiogeography. This research will address fundamental questions related to plant evolution and ecosystem dynamics in deep time. As such, it will lead to advances in the understanding of past organisms and their environments, shedding light on the origin of today’s biodiversity and on ecosystem responses to past environmental changes.