Whole-plant reconstruction of an early Devonian lycophyte

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Plants of the Early Devonian epoch (419-323 million years ago) are crucial to reconstructing the initial radiation of tracheophytes, yet few are understood as whole organisms. Unearthing the habits of Sengelia radicans, Matsunaga and Tomescu integrate morphometric data from hundreds of fossil specimens from the Beartooth Butte Formation (Wyoming, USA) with taphonomic and sedimentological observations at the fossil outcrop.

Whole-plant reconstruction of Sengelia radicans.
Whole-plant reconstruction of Sengelia radicans. The reconstruction shows one Sengelia individual to emphasize the prostrate or creeping habit in which stems are erect only near shoot tips, in accordance with the non-self-supporting nature of larger stems. Frequent and sometimes reiterative K-branching produced an extensive shoot system that formed dense mats of stems on the ground. Root-bearing axes are shown growing either along the substrate before growing downwards, or straight downwards from the base, and have sparse reduced leaves near the base. Dichotomously branching roots extend laterally from the root-bearing axes. Successive K-branching is depicted at variable intervals, with longer intervals on larger stems and with the number of K-branches relative to total stem length matching the morphometric data from this study. Leaf sizes and densities relative to stem size are also consistent with the morphometric data. Sporangia (yellow dots) are sparse and aggregated into loosely defined fertile areas. The underlying stem mat layer (bottom right) represents a previous Sengelia population buried in situ by a major flood event, consistent with the stratigraphic sequence observed at the outcrop at Cottonwood Canyon. Root-bearing axes are shown diverging downwards from it. The reconstructed Sengelia plant is depicted colonizing the sediments that buried the previous population. Scale bar = 10 cm.

Providing a rare window into the morphology, life history (adapted for survival after floods) and growth environment of an early vascular plant, this study adds to the diversity of body plans documented among lycophytes and may help with elucidating patterns of morphological evolution in the clade.

Reference

Matsunaga, K. K. S., & Tomescu, A. M. F. (2017). An organismal concept for Sengelia radicans gen. et sp. nov. – morphology and natural history of an Early Devonian lycophyte. Annals of Botany, 119(7), 1097–1113. https://doi.org/10.1093/aob/mcw277


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