This is the oldest direct evidence for a rooting system preserved in growth position. These rooting systems, which can be traced to a parent plant, include some of the earliest roots known to date and demonstrate that substantial plant-substrate interactions were under way by Early Devonian time. The morphological relationships between stems, root-bearing axes and roots corroborate evidence that positive gravitropism and root identity were evolutionarily uncoupled in lycophytes, and challenge the hypothesis that roots evolved from branches of the above-ground axial system, suggesting instead that lycophyte roots arose as a novel organ.

Data Repository Figure 2 (DR2).  18 O w vs. Paleo-Latitude  18 Ow vs. Paleo-Latitude for samples measured in this study. For comparison, two typical assumptions of  18 Ow are shown. These are 1)  18 Ow =-1.0‰ (VSMOW) everywhere (solid line), representing an ice-free world (Shackleton and Kennett, 1975); or 2) the ice-free value adjusted to account for the modern meridional gradient in  18 Ow (dashed line) (Zachos et al, 1994), giving-0.4 to-1.1‰ (VSMOW) for the latitude range covering the WIS. The data show much more variability than predicted by either of these traditional assumptions, potentially explaining why early attempts at reconstructing WIS paleotemperatures failed to produce reasonable temperatures when they assumed a constant  18

Sengelia radicans is the oldest among the very few early tracheophytes for which a detailed, rigorous whole-plant concept integrates morphology, growth habit, life history and growth environment. This plant adds to the diversity of body plans documented among lycophytes and may help elucidate patterns of morphological evolution in the clade.

Honeggeriella adds a lichen component to one of the richest and best characterized Early Cretaceous floras and provides a significant addition to the sparse fossil record of lichens. As a heteromerous chlorolichen, it bridges the >350 million-year gap between previously documented Early Devonian and Eocene occurrences.

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