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Additional Resources:

Family:

Roccellaceae (Ascomycota)

Accepted Name:

This name is currently accepted.

Description:

Type: - USA. ARKANSAS. SEARCY CO.: Buffalo National River, Tyler Bend along River View Trail from Collier Homestead Trailhead, 35°58'31"N, 92°45'56"W, dolomite bluffs in hardwood forest, on vertical dolomite bluff, 17.iv.2005, Buck 48756 (NY, holotype).

Description: (From Harris & Ladd 2007) - Thallus placodioid, composed of +/- bullate or rugose, irregularly polyhedral or irregular areoles, light to dark or brownish orange, K+ violet-black (violet in section), not pruinose; areoles to +/- 1.0 mm across and to 1.0 mm thick; prothallus absent. Chemistry: unknown pigments (2 yellow spots + 1 purple spot in solvent A). Photobiont Trentepohlia, cells subglobose to ellipsoid, 14–20 x 9–12 µm. Epicortex gelatinous, orange pigmented above, +/- colorless below, almost absent to ca. 10 ìm thick, Cortex cartilaginous, colorless, 20–30 µm thick, of tightly interwoven, highly gelatinized hyphae, I+ blue-green; orange pigment K+ violet, forming small deep violet granules. Medulla both above and below algal layer, white, filled with small colorless crystals obscuring sparse hyphae (not dissolving in K), K–, C–, KC–, PD–; upper part 40–60 µm thick, of loose, mostly anticlinal?, thick walled, I+ blue green hyphae; lower part thick, to ca. 1.0 mm high, white, I+ dark bluegreen. Algal layer 75–100 µm thick. Apothecia opegraphoid, black, sessile, on or between areoles, 0.5–1.2 mm across, initially +/- rounded but often deformed, occasionally +/- elongated, scattered or occasionally clustered or proliferating along margins, initially immersed in thallus; margin black, rarely orangish pruinose, raised, coarse, becoming sinuate in older ascomata; disk black, orangish pruinose. Exciple black, highly melanized, 45–70 µm thick. Hypothecium dark brown, extending slightly into thallus, ca. 250 µm thick.. Epihymenium with sparse to dense orange granules, dark brown in K. Hymenium tinted and streaked with light brown or orange-brown, with scattered colorless or orange crystals, upper part I+ dark blue-green, lower I+ red orange, ca. 100–110 µm high. Paraphysoids branched and anastomosed; tips not expanded. Asci clavate, aborted/old ones with orangish brown to orange contents, with 8 spores mostly in two rows. Ascospores 3-septate, colorless, halonate, becoming brown and coarsely ornamented, 16–20 x 5–6.5 µm (excluding halo). Pycnidia not found.

Etymology: (From Harris & Ladd 2007) - Phoebus = Greek sun god, suggested by the orange “sun bursts” on rock in otherwise dark places, hydrophobius = water fearing, for its ecological preference.

Distribution and ecology: (From Harris & Ladd 2007) - Restricted to massive calcareous substrates, typically on vertical faces of dolomite and limestone in areas of moderately high light intensity but protected from direct runoff or wetting. A typical habitat is on the face of a large bluff where a bedding plane of less resistant limestone has weathered more rapidly than the surrounding bedrock, creating a slightly recessed zone protected by the overhanging bedrock above. It occurs on both high light exposures and moderate shade. Because of the restricted habitat, this species is known from only a few sites in the southwestern Ozarks, as well as from nearby eastern Kansas and the Edwards Plateau of Texas, where it was discovered during the 2005 ABLS Foray. Attempts to relocate the population at the site Cherokee County, Kansas documented by Kramer in 1954 have been unsuccessful.

Discussion: (From Harrs & Ladd 2007) - In the field one is likely to mistake the orange thallus of Phoebus for an orange species of Caloplaca Th. Fr. Both also react magenta to purplish in K, but Phoebus has a much darker color reaction. When fertile, opegraphoid ascomata and ascospores easily distinguish Phoebus. Sterile material can be recognized by the very dark K-reaction and Trentepohlia photobiont. It is possible that Phoebus represents a lichenicolous Opegrapha on another sterile species of Roccellaceae but there is no hint of damage or two types of hyphae associated with apothecia. Within the Roccellaceae the placodioid thallus suggests some of the Southern Hemisphere species of Roccellina Darb. However, it does not seem closely related to that genus due to the unique thallus pigmentation and anatomy. As far as we can tell there is no other genus in the family with anthraquinone-like pigments in the thallus or a well developed medullary layer above and below the algal layer.