A New Zosterophyll with Novel Emergence and Cuticle Features from the Early Devonian of New Brunswick, Canada

Premise of research. Vegetative and fertile axes of a zosterophyll are described from the Emsian of northern New Brunswick exhibiting distinctive emergence and cuticular features and are assigned to Staphylophyton semiglobosa, gen. et sp. nov., thus adding yet another plant with a distinctive combination of characters to class Zosterophyllopsida. Methodology. Specimens were prepared by d & eacute;gagement and maceration to expose both vegetative and reproductive features. LM, SEM, and confocal laser scanning microscopy were used to analyze specific morphological and cuticular patterns of fossils. Arabidopsis stems with trichomes were stained for cellulose and cutin and imaged to determine whether cuticle extends across a trichome base or its subtending cell, in order to better interpret rosette cuticle patterns. Pivotal results. Branched and unbranched axes up to 10.6 cm long and 2.2-5.8 mm wide either lack sporangia or bear lateral sporangia on short stalks. Axes are densely covered with semiglobose and conical emergences on all sides. Sporangia consist of two unequal-sized valves: a larger, more rounded outer valve covered with emergences and a smaller, smooth inner valve. Sporangia are borne on one or two sides of the axis and are slightly angled upward. Cuticle shows epidermal cell outlines on both axes and emergences, with those on axes being elongate-rectangular and those on emergences consisting of smaller polygonal cell outlines among which are interspersed ovoid cell outlines consisting of thinner, usually continuous cuticle. Undoubted stomata were not observed on the numerous prepared cuticles with preserved cell outlines and thus either were not preserved or were absent. The Arabidopsis experiments showed no evidence of cutin at the base of, or beneath, hairs where they depart from a stem, suggesting that rosette cell patterns represent something other than hair bases. Conclusions. This new taxon adds to the known diversity among zosterophylls, and while distinctive enough to be recognized as a new taxon, Staphylophyton exhibits branching and sporangial features very similar to Sawdonia spp. and may be closely related. These apparently aerial axes, in which cuticular features are comparatively well preserved both in stems and in emergences, are puzzling in lacking evidence of stomata. If truly absent, some alternative means of carbon uptake might include (1) CO2 diffusion across the many thinner cuticularized cells to allow photosynthetic carbon fixation, (2) uptake of aqueous CO2 from (as yet unknown) underground structures, or (3) mycoheterotrophy or parasitism.