The Brymbo fossil forest was dominated by giant tree-like lycopsids (more closely related to diminutive club-mosses than modern trees), estimated to exceed 90 feet in height, including the genera lepidodendron and Sigillaria. The stumps and rooting systems of these trees are preserved in situ, the largest reaching two meters in height and the roots expanding 5 meters across.
Interspersed in the sandstone layers are thickets of several species of calimatian horse tails, including their fine rooting systems and occasional branching structures, the exact palaeobiology of which is still contested (did they branch aerially or in the leaf-ridden ‘duff’ layer of the forest floor?).
In the grading mud-sandstone layers horizons of abundant medullosalid fern leaves and Annularia (the delicate leaf-structures of calamites) occur, alongside the strap like leaves of the extinct gymnosperm Cordaites.
Though currently rare in this facies (technical term for a recognisable group of rock layers), anamal fossils have been recovered; several examples of an as-yet unidentified pygocephalomorph crustacean and a single small xiphosuran (Euproops sp.). It is expected that a dedicated effort to crack the thousands of siderite concretions recovered so far will undoubtedly yield not only more fabulously preserved plant remains but hopefully more arthropod fossils, increasing our picture of the diversity supported by this ancient forest.