Zeilleria delicata

Zeilleria delicata is a species of extinct true fern known from the Late Carboniferous period, primarily found in the coal-bearing strata of Europe. Belonging to the family Botryopteridaceae, it is considered a small, delicate member of the eusporangiate ferns, and is typically interpreted as a close relative of Renaultia and other early marattialean ferns (Galtier, 1981; Taylor et al., 2009).

This species is best known from anatomically preserved material, often recovered from calcareous coal balls or siderite nodules where its internal tissues have been finely fossilised. The stems of Z. delicata are generally slender and upright, with a solid vascular stele and an abundance of leaf trace divergences, indicating it supported a densely fronded canopy. The cortex is notably thin in comparison to other botryopterid ferns, suggesting a more gracile habit, possibly as a component of the understorey in swampy Carboniferous environments.

The fronds of Zeilleria delicata are finely dissected and relatively small, consistent with its name and presumed growth form. Fertile specimens show the presence of eusporangiate synangia—fused sporangial clusters borne on the lower surfaces of specialised frond segments. These synangia are a diagnostic feature of Marattiales and are key in distinguishing Zeilleria from superficially similar seed ferns and leptosporangiate ferns (Stewart & Rothwell, 1993).

Palaeoecologically, Z. delicata is interpreted as an understorey fern, adapted to shaded, humid conditions beneath the towering canopies of lycopsids, tree ferns, and seed ferns. Its small size and fine frond morphology suggest it played a role in ground-level foliage coverage and spore dispersal in swamp forest ecosystems.

The genus is named in honour of Charles René Zeiller (1847–1915), a French palaeobotanist known for his extensive work on the fossil flora of the Carboniferous coal basins of France and Belgium.