Fern-like Plants Establishing the Understory of the Late Devonian Xinhang Lycopsid Forest.

Abstract

Forests appeared during the Middle to Late Devonian, but Devonian forests and their compositions are still rarely known. Xinhang forest was reported as the largest Devonian forest, with lycopsid trees of Guangdedendron micrum Wang et al. A fern-like plant Xinhangia spina Yang and Wang with shoots and anatomy, was previously described from this forest, but its habit and ecology remain unclear. From Xinhang forest, we now report more specimens of fern-like plants including X. spina and some unnamed plants in several beds. Prominent adventitious roots, spines and secondary xylem indicate that the stems of X. spina are largely procumbent to function as anchorage, absorption and support. Other fern-like plants with distinct roots or multiple slender branches also suggest procumbent habits. Xinhang forest is thus reconsidered as multispecific with a canopy of lycopsid trees and understory of diverse fern-like plants, which are adapted to the disturbed coastal environment. The composition of Xinhang forest may indicate a structural transition of the early forests' dominator from fern-like plants to lycopsids.