Leptogium marcellii
Leptogium marcellii is a species of gelatinous lichen in the family Collemataceae. It was described in 2018 from the South Shetland Islands, Antarctica. It has overlapping with small, flattened, a distinctly hairy underside, and a soft, gelatinous interior that swells when wet. Internally, its fungal threads are arranged in a loose, sponge-like network around the cyanobacteria rather than as neat vertical "columns", a key trait used to separate it from similar Antarctic species. Apothecia, when present, have rims that are ornamented when young and develop lobules with age.
Taxonomy
The species was described as new in 2018 by Marcos Junji Kitaura, Aline Pedroso Lorenz‑Lemke, and Adriano Spielmann. The holotype was collected on mosses at Dufayel Island in Ezcurra Cove, King George Island, South Shetland Islands at 16 m elevation; the type is housed in the herbarium of the Federal University of Mato Grosso do Sul. The species name honours the Brazilian lichenologist Marcelo Pinto Marcelli.The authors used an integrative approach and obtained ITS and mtSSU sequences for two specimens of L. marcellii. In the resulting phylogenetic trees, L. marcellii forms a well-supported lineage closely related to the Antarctic pair L. puberulum and L. tectum.
Description
The thallus is foliose and typically around 4 cm across and 85–125 micrometres thick, dark brown to blackish in reflected light and brownish to greenish grey under a stereomicroscope. are up to about 4 mm wide; they overlap towards the margins and often turn slightly upwards. The lobe margins are smooth to and can look "crisped". Isidia are absent, but flattened lobules are frequent on the margins and may also occur on the upper surface and along the rims of fruiting bodies.Attachment is by both simple hairs and longer beard-like hairs on the lower side; rhizines and are absent. The upper surface is smooth to slightly wrinkled; the lower is . In section, the medulla shows loosely packed hyphae in a sponge-like arrangement filled with cyanobacteria; unlike some relatives, there are no columnar hyphae. This internal pattern is one of the most reliable diagnostic for the species.
Fruiting bodies were seen in additional material from Livingston Island. They are up to about 2.5 mm across, with a concave ; the rim is initially ornamented with small wart-like structures and later bears lobules. Ascospores are spindle-shaped, typically 20–25 × 5–7.5 μm; pycnidia occur on the thallus and produce slender conidia about 5 × 1.25 μm.