Structurally complex, yet anatomically plesiomorphic: permineralized plants from the Emsian of Gaspe (Quebec, Canada) expand the diversity of Early Devonian euphyllophytes

The Battery Point Formation of eastern Canada hosts an Emsian (c. 400-395 Ma) flora that marks one of the rare occurrences of anatomically-preserved Early Devonian plants. We describe four new euphyllophytes from small permineralized axes in this unit. Leptocentroxyla tetrarcha gen. et sp. nov. has a four-ribbed mesarch actinostele with Psilophyton-type (P-type) tracheids and a central area of scalariform tracheids. Stenoloboxyla ambigua gen. et sp. nov. has a bar-shaped to three-ribbed mesarch stele lacking central protoxylem, with one of the ribs less pronounced, P-type tracheids, and sclerenchyma forming a discontinuous layer in the cortex. Jowingera triloba gen. et sp. nov. has a three-ribbed mesarch actinostele with central protoxylem and P-type tracheids. Tainioxyla quebecana gen. et sp. nov. has bar-shaped xylem with mesarch protoxylem strands, P-type tracheids, and anatomy typical of cambial growth initiation. These new species raise the diversity of Battery Point Formation permineralized plants to nine genera, adding significantly to the diversity of Early Devonian plants characterized anatomically. The four species encompass structural diversity of unexpected breadth and novelty for their age. They are different from both older and coeval euphyllophytes and from younger euphyllophytes, exhibiting combinations of derived and plesiomorphic characters. Their mesarch actinosteles and bar-shaped protosteles, histological differentiation within metaxylem and cortex, and secondary growth, represent aspects of structural complexity common in more derived Middle-Late Devonian euphyllophytes. Concurrently, the four species share P-type tracheids typical of Early Devonian basal euphyllophytes with simpler anatomies. These new fossils offer a first glimpse of a plexus of plants representing a previously unsuspected stage of euphyllophyte morphoanatomical evolution. They demonstrate significant euphyllophyte diversification and exploration of structural complexity under way during the Early Devonian, against a background of plesiomorphic-type tracheids. When more completely characterized, these Emsian plants will provide links for resolving phylogenetic relationships at the base of the euphyllophyte clade.