Galtiera bostonensis, gen. et sp. nov., a protostelic calamopityacean from the New Albany shale of Kentucky

Abstract

Two parts of a single, anatomically preserved stem fragment form the basis of a new Lower Mississippian taxon that is characterized here in detail. Stelar morphology, leaf trace departure, secondary xylem, outer sparganum cortex, and Kalymma-like leaf bases provide evidence of taxonomic relationship with the Calamopityaceae. The primary vascular column is deeply three ribbed with protoxylem strands restricted to the periphery of the xylem. Trace departure is associated with a dextral shift in the position of primary xylem ribs such that the tip of each rib describes a helical course through the axis. The result is a Fibonacci phyllotactic fraction of at least 2/5. On the basis of our observations, we hypothesize that the protoxylem strands may comprise five sympodia and, further, that although protostelic in gross morphology, the primary vascular system of Galtiera might actually be more similar to typical eusteles of the Calamopityaceae than protosteles of any other major group. Sclerotic clusters and strands in the cortex are of interest because they are unusually numerous and are usually associated with the phloem either of the main stem vascular column or of leaf traces. The evidence is consistent with the hypothesis that this morphology reflects a pathological response by the plant to viral or other infectious agents.