Aspects of Growth and Development in the Pennsylvanian Age Marattialean Fern Psaronius

Abstract

Numerous specimens from several species of the Paleozoic marattialean fern genus Psaronius Cotta were collected from Upper and Middle Pennsylvanian deposits in Ohio, Illinois, and Kansas. I suggest that, as the Psaronius plant grew, basal portions of the stem and bound root zone decayed. This conclusion is based on specimens in which the stem and bound root zone are completely or partially lacking, the paucity of very basal trunk segments known for the genus, and evidence from living analogs. Secondary parenchyma in P. chase Morgan and P. blicklei Morgan is described as localized areas of radially aligned cells in stems and outer cortex. Linear regressions of number of orthostichies, stelar cycles, and inner meristeles versus stem diameter indicate that vascular ontogeny may have occurred at different rates among some species of Psaronius. Analysis of Psaronius stem anatomy and morphology suggests that, in general, stems had an open, unidirectional growth mode with a continuously expanding apex and vascular tissue of both cauline and foliar origin.

Paleobotany supports the floating mat model for the origin of Carboniferous coal beds

“…The small sizes of the specimens described here, a relatively simple stelar anatomy, attachment of petioles, and the lack of a root mantle suggest that they are basal Sanders and Austin ◀ Paleobotany supports the floating mat model ▶ 2018 ICC portions of relatively young, small sporophytes. (p.837) Mickle (1984) in his analyses further confirms this, "Analysis of Psaronius stem anatomy and morphology suggests that, in general, stems had an open, unidirectional growth mode with a continuously expanding apex and vascular tissue of both cauline and foliar origin" (p. 407). Also, "With a few exceptions, however, the typically expanding vascular structure suggests that the cauline apex in Psaronius stems was continuously increasing in size" (p. 417).…”

“…All known specimens of Psaronius lack the very base of a stem and none show roots penetrating or encased in soil (Ehret and Phillips 1977;Mickle 1984;Millay 1997;Morgan 1959;Stidd and Phillips 1968;Weiss 2011). Mickle (1984) discovered that fossils of the stem-mantle segments farthest from the stem apex either had the stem and bound roots rotted away, leaving a thick free-root "doughnut," or the "doughnut" was plugged by the stem and bound root layer only on the upper side of the "doughnut." Thus, it is clear that the stem and attached bound roots rotted away Sanders and Austin ◀ Paleobotany supports the floating mat model ▶ 2018 ICC while the free root zone remained as the structural support at the base.…”

“…As the plant grew from a sporeling to a large plant, the diameter of the stem increased gradually, the stele became more complex, and the leaves in the crown became more and more numerous, and the basal root mantle continued to increase in thickness (Ehret and Phillips 1977;Mickle 1984;Millay 1997;Morgan 1959;Stidd and Phillips 1968;Weiss 2011). Thus, the stem of Psaronius was a narrow, upwardly thickening cane that was supported entirely by a downward thickening buttressing jacket of adventitious roots (Figure 3).…”

“…In his analysis of development of Psaronius plants (see his Figures 1-6), Mickle (1984) stated, I suggest that, as the Psaronius plant grew, basal portions of the stem and bound root zone decayed. This conclusion is based on specimens in which the stem and bound root zone are completely or partially lacking, the paucity of very basal trunk segments known for the genus, and evidence from living analogs.…”

“…(p. 409). Mickle (1984) mentions very limited decay of the sporeling stem base in the tree ferns Angiopteris and Cyathea, "The decay of proximal stem segments in modern [especially rhizomatous] ferns is analogous to basal stem and root mantle decay in Psaronius…. Many rhizomatous plants [i.e, non-tree ferns] e.g., Pteridium aquilinum, may have decaying proximal segments while the meristem continues to grow".…”