Fissurina confusa

The thallus forms a crust on bark, typically 1–3 cm across and about 50–100 μm thick. It forms a continuous crust with an uneven to warty, blistered (bullate) surface, ranging from yellowish green to olive-brown. The photobiont (the photosynthetic partner) is a trentepohlioid alga (Trentepohlia-type). The lirellae are straight to curved and usually unbranched (sometimes sparsely branched). They become erumpent (breaking through the thallus surface) and prominent. Individual lirellae are about 0.5–1 mm long and 0.15–0.2 mm wide, with a lateral thalline margin. The disk is partly exposed and often gray-pruinose (with a powdery coating), while the labia are thick and white. Microscopically, the asci are fusiform (spindle-shaped) and typically contain eight ellipsoid ascospores. The spores are muriform (divided by many internal walls), with about 5–7 transverse rows and 1–3 longitudinal septa, and measure about 25–35 × 12–20 μm. The ascospores are amyloid (I+ violet-blue), meaning they stain in iodine-based tests. Chemically, the thallus contains psoromic acid (major) together with subpsoromic acid (minor) and 2'-O-demethylpsoromic acid (major). The medulla reacts P+ (yellow) in standard spot tests.

Similar species. Fissurina confusa resembles several bark-dwelling species in the genus that share slit-like lirellae and muriform ascospores. …

Fissurina confusa is known from several collections in Fakahatchee Strand Preserve State Park on branches of hardwoods. Similar material had previously been reported from Brazil under the name Fissurina instabilis; F. confusa was treated as part of a small group of muriform-spored species in the genus that contain psoromic acid.

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