Thalassites parkavonensis Benzecry et Brack-Hanes

Plant Fossil Names Registry Number: PFN003643

Act LSID: urn:lsid:plantfossilnames.org:act:3643

Authors: A. Benzecry & S. D. Brack-Hanes

Rank: species

Genus: Thalassites Benzecry et Brack-Hanes

Reference for this name: Benzecry, A. & Brack-Hanes, S. D. (2008): A new hydrocharitacean seagrass from the Eocene of Florida. – Botanical Journal of the Linnean Society 157(1): 19–30.

Page of description: 24

Illustrations or figures: Figs 1–15

Original diagnosis/description

Dimorphic rhizome system. Striated, monopodial plagiotropic rhizome with closed annular scars at nodes and unbranched, straight roots at wide
and irregular intervals along internodes. Bifurcated orthotropic short shoots at regular nodal intervals along the rhizome. Amplexicaulous leaf scars on short shoots at regular intervals in an alternate pattern and distichous arrangement. Leaves arranged in terminal clusters. Leaves are eligulate and non-fibrous with a persistent, fibrous basal sheath. Strap-shaped leaf blades with entire margins, rounded apices, narrow parallel veins with perpendicular and oblique cross veins, and a prominent median vein. Crystals and tanniferous cells are abundant throughout the plant.
Description: Dimorphic rhizome system with striated, monopodial, plagiotropic rhizome 5–10 mm in width; internodal distance constant (10–12 mm); closed annular scars at nodes and fine, straight, unbranched roots infrequent at internodes; epidermis of differentially thickened elongate cells in files parallel to the long axis, cortex spongy. Orthotropic, bifurcated, short shoots about 3–6 mm wide in pairs every three to five nodes. Epidermis of short shoots with differentially thickened, almost isodiametrical (cuboidal) cells and a cuticle; spongy cortex with longitudinal bundles of fibres; crystals and tannins abundant. Terminal clusters of six to eight, strap-shaped, eligulate leaves almost encircle short shoots in alternate and distichous arrangement. Non-fibrous leaf blades (15–19 mm wide) have entire, smooth margins and rounded apices. Leaf venation parallel (27–30 veins) with perpendicular and oblique cross veins. Median vein is prominent. Fibrous, amplexicaulous, basal leaf sheath (15–19 mm wide and 30–45 mm long) is persistent. Leaf epidermal cells are elongate to cuboidal and have straight, thin walls. Tanniferous cells are profuse and in circular aggregations. Crystals are
abundant.

Etymology

Derivation: Stratigraphy of the type specimen (Avon Park Formation).

Stratigraphy

Paleogene, Eocene
Avon Park Formation, Claiborne Stage, Late Middle Eocene (Vernon, 1951).

Locality

United States
Florida Rock Industries dolomite/limestone quarry, approximately 1.5 miles south of Gulf Hammock (sec. 28, T14s, R16s), Levy County, Florida,
on east side of US Highway 19.