A new zosterophyll from a recently discovered exposure of the Lower Devonian Senni Beds in Dyfed, Wales*

Abstract

Coalified remains of a plant with pseudomonopodial and isotomous branching in hairy axes, and with lateral sporangia arranged in one or two rows in an extended fertile zone, are placed in a new genus of the Zosterophyllophytina. Evidence for an exarch xylem strand, elliptical in transverse section, derives from pyrite permineralizations. The new genus is close to Gosslingia Heard in the precise distribution of its sporangia with respect to branching and in the possession of axillary tubercles, but it differs in the attitude of its sporangia and their frequent arrangement in two rows. An appraisal of characters used in the delimitation of zosterophyll genera leads to the conclusion that it is premature to subdivide the group into families. Comparison with pyritized tracheids in Gosslingia indicates that those in the new plant possess both annular and spiral secondary thickenings which are indirectly connected and are thus considered typical of zosterophyll water-conducting elements. The more variable appearance of tracheids in the new taxon is attributed to increased decay before permineralization.