Tomescu, Alexandru Mihail Florian , Rothwell, Gar W. , Trivett, Mary L. .
Reconstructing a stem-group filicalean fern with reiterative indeterminate growth of the fronds.
Foliar members with attached plantlets and fertile frond systems conforming to morphospecies Anachoropteris clavata, from the Pennsylvanian of Ohio and Illinois are used to reconstruct the whole-plant. The stem is known from epi-petiolar shoots that feature a terete protostele with exarch xylem maturation. The shoots arise laterally, at different positions along frond rachises, and bear adventitious roots. Frond architecture is modeled on the morphology of latent crosiers, and reconstructed from the four orders of pinnae. Fronds are planar and pinnate, with alternate branching. Vascular traces of all frond members have adaxial, exarch protoxylem. Rachises and primary pinnae have adaxially convex C-shaped traces with swollen ends of the arms, whereas traces of secondary pinnae are simple and flattened in the plane of the leaf. Pinnules, representing the tertiary pinnae are laminar, with lobed margins, and dichotomous venation. Latent crosiers arise on otherwise mature frond segments at the position of primary or basalmost secondary pinnae. Crosiers have four orders of branching, equivalent in complexity to a whole frond. Fronds bear abaxial, superficial sori of annulate leptosporangia enclosed by globose indusia. Vascularized soral receptacles bear numerous sporangia on elongated, uniseriate stalks. Sporangia have vertically oriented C-shaped annuli of 2-3 rows of cells. Numerous trilete spores are produced in each sporangium and the soral maturation is gradate. Fronds of indeterminate growth dominate the organography of this plant, generating a growth architecture that combines features of a scrambling habit (shoots produced on frond rachises), with those of climbing vines (modular, reiterative growth by latent crosiers). Initially assigned to the Coenopteridales, this fern combines many features characteristic of several extant filicalean families (Osmundaceae, Schizaeaceae, Gleicheniaceae, Cyatheaceae, Hymenophyllaceae, and Polypodiaceae s.l.), which suggests the existence of an extinct grade or clade of stem group Filicales.
1 - Ohio University, Department of Environmental and Plant Biology, Porter Hall, Richland Avenue, Athens, Ohio, 45701-2979, USA
Presentation Type: Paper
Location: Maybird (Cliff Lodge)
Date: Wednesday, August 4th, 2004
Time: 11:30 AM