Speerschneidera euploca

The thallus of Speerschneidera forms regular, circular rosettes about 7–12 cm across. These are built from narrow lobes 0.2–0.5 mm thick that usually branch in two at short intervals; three-way branching is uncommon. The upper surface is smooth and grey to brownish-grey (turning grey-green when moist), while the underside is paler and has a fine, fibrillar texture. The thallus is attached to the rock at irregular intervals by adhesive strands. In cross section, much of the thallus is occupied by a strongly developed upper cortex of densely interwoven fungal tissue (scleroplectenchyma). This layer is typically 180–230 μm thick and makes up about one-half to four-fifths of the thallus thickness, while the lower cortex is thinner, at about 50–70 μm. The green algal partner is embedded in the medulla in clusters about 100 μm tall, interspersed with fungal hyphae. Josef Poelt interpreted the prominent, hyaline strand-like tissues in Speerschneidera as functioning mainly in water retention rather than acting purely as a mechanical support. Apothecia develop chiefly in the branch axils (less often near lobe tips or edges) and, as they mature, may appear centred on the narrow lobes. Mature apothecia are about 0.5–2.0 mm across with a flat to sometimes convex, reddish-brown disc, and they are built in the lecanoralean manner. …

Speerschneidera euploca grows on calcareous rock, typically on shaded, steep, north-facing exposures, and is rarely collected and apparently uncommon. When dry it is easily overlooked because its color blends with limestone, but when wet it becomes bright green. In central Texas it was reported from juniper-shaded north-facing outcrops, growing alongside Dermatocarpon minimum and species of Collema and Verrucaria. Hafellner and Egan recorded it from the St. Louis area of Missouri south-west through Kansas, Oklahoma and Texas to a single locality in Jalisco, Mexico, with no records reported outside the United States and Mexico.

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