Equisetum dimorphum Elgorr., Escapa et Cúneo

Plant Fossil Names Registry Number: PFN003086

Act LSID: urn:lsid:plantfossilnames.org:act:3086

Authors: A. Elgorriaga, I. H. Escapa & N. R. Cúneo

Rank: species

Reference: Elgorriaga, A., Escapa, I. H. & Cúneo, N. R. (2015): Reconstruction and phylogenetic significance of a new Equisetum Linnaeus species from the Lower Jurassic of Cerro Bayo (Chubut Province, Argentina). – Ameghiniana 52(1): 135–152., link

Page of description: 138

Illustrations or figures: figs 2–8

Types

Original diagnosis/description

Stems unbranched, externally smooth, and internally hollow except at the nodes. Complex nodal septa, with external diaphragm portion circular, flat, bearing pitted microrelief in a vague radial arrangement, surrounded by an internal ring of carinal canals and an external ring of vallecular canals; internal diaphragm part with robust tissues forming an upwardly convex structure resembling a cart-wheel, with a central hub, radiating spokes, and a thin peripheral rim of scalloped appearance; polygonal cells with thickened walls occur at the hub and the spokes. Nodal leaf whorls consisting of a fused basal sheath and free, lanceolate, usually spreading, distal leaf tips; sheath portion comprising usually 75–80% of the total leaf-length, with bicarinate commissural furrows composed of a sunken central region with large, transversely oriented cells bounded by oblique flanks with obliquely oriented cells. Number of leaves, vallecular canals, and spokes usually between 12 and 42. Stem apices commonly terminating in pagoda-like structures.
Internodal epidermal cells are square to rectangular, in longitudinal rows; stomata usually sunken and distributed in broad bands. Strobili single, terminal, cylindrical to oblong, with whorls of densely arranged sporangiophores bearing penta- or hexagonal distal shields with a central umbo and abaxial sporangia; strobili subtended by heteromorphic leaf whorls with their tips at least three to four times longer than those of regular leaf whorls.

Etymology

The specific epithet (gr. dimorphos= having two forms) is chosen in reference to the distinctly different morphology of apical leaf whorls of fertile stems; it furthermore appropiately describes the two different preservational aspects of the nodal region

Stratigraphy

Jurassic, Lower Jurassic, Pliensbachian

Locality

Argentina
Cerro Bayo area, NW Chubut Province