Acarospora alba K. Knudsen, Kocourk. & Hodková, 2025

Knudsen, Kerry, Cho-Ah-Ying, Jessica, Kocourková, Jana, Hodková, Eva, Malíček, Jiří & Wang, Yan, 2025, The diversity of Acarosporaceae (Acarosporales, Lecanoromycetes) in California, MycoKeys 112, pp. 183-210 : 183-210

Acarospora alba K. Knudsen, Kocourk. & Hodková sp. nov.

Fig. 2

Type.

U. S. A. • California: Riverside Co., Joshua Tree National Park, Mojave Desert, Sheep’s Pass , at base of Ryan Mountain , on gentle west-facing slope covered with small rocks and pebbles of granite and gneiss, 34.001, - 116.1268, alt. 1369 m, on granite, 20 Dec 2010, K. Knudsen 13222 (holotype-SBBG) .

Diagnosis.

Similar in having a non-stratified thallus like the possibly extinct central European species Acarospora variegata but differing in not producing gyrophoric acid, not developing a distinct cortical layer which is poorly developed in A. variegata , and having an opaque white upper surface, not translucent in water.

Etymology.

Named for the white non-translucent upper surface of the unstratified thallus.

Description.

Thallus growing in the upper layer of substrate, endolithic to epilithic, covering 1–3 cm in width, an unstratified matrix of gelatinized intricate to anticlinal hyphae, 1–4 µm wide, intermixed with substrate crystal, with thin cracks splitting the upper layer into areoles irregular in shape, 0.3–1.0 mm wide, 200–400 µm thick. Upper surface ecorticate, white, epruinose, sometimes with small pale patches of reddish-brown pigment observed in thin sections at 1000 ×, not translucent when wet. Algae scattered or in thin clusters, algal cells 7–16 µm wide, not forming a continuous algal layer. Apothecia 0.1–0.5 mm wide, usually one per areole, oval to irregular in shape, disc black when dry, dull reddish brown when wet or not changing color, epruinose to lightly pruinose, rugulose or smooth, immersed and even with thallus surface or emergent and elevated above the thallus surface, with a thin white thalline margin 20–50 µm wide. Parathecium 10–40 µm wide, hyphae 2 µm wide, sometimes visible as parathecial ring around apothecial disc same color as epihymenium. Hymenium (100 –) 120–150 µm tall, cupular, usually tallest in center, epihymenium ca. 10 µm tall, reddish-brown, paraphyses mostly 1 µm wide, not branching, apices unexpanded, hymenial gel IKI + blue to red, hemiamyloid. Asci 80–90 × 22–26 µm, clavate, ascospores mostly 3–4 × 2 µm, ellipsoid, several hundred per ascus (n = 20). Subhymenium 20–25 µm tall, IKI + blue, euamyloid. Hypothecium Y-shaped, the central axis of hyphae extending down in a bundle, the arms 15–30 µm thick embracing the V-shaped subhymenium and continuous with parathecium. Pycnidia not observed. Chemistry: not producing secondary metabolites.

Habitat and distribution.

Known only from two locations on granite in full sun in the Mojave Desert in Joshua Tree National Park at approximately the same elevation of 1347–1369 m. The two specimens were collected about ten miles from each other. The sequences of the paratype were contaminated by a common parasitic lichenicolous fungus in Joshua Tree National Park, Acarospora destructans , though the parasite had not produced apothecia, and the thallus of A. alba showed no signs of contamination ( Knudsen et al. 2022 a). Sequences were only obtained from the holotype. Based on extensive collecting in Joshua Tree National Park since 2005 by Knudsen and Kocourková, the species is considered rare ( Knudsen et al. 2013; Knudsen and Kocourková 2023).

Additional specimen examined.

U. S. A. • California, Riverside Co., Joshua Tree National Park, Mojave Desert , off trail between Skull Rock and Jumbo Rocks, 33.9958, - 116.0653, alt. 1347 m, on granite, 19 Dec 2010, K. Knudsen 13181 ( SBBG) .

Notes.

The white pigmentation of the thallus, like the white layer of pruina on Acarospora peltastica , increases surface albedo to protect the algal layer in the intense sunlight of the desert. Acarospora alba has a non-translucent white surface when wet while the white layer of A. peltastica is translucent when wet, the brown from a pigmented lower layer visible through the transparent pruina and epicortex. In our current key of Acarosporaceae of southwestern North America A. alba is recovered in section 8, couplet 8, with A. arenacea and A. bolleana , both with non-translucent white surfaces. Acarospora arenacea has euamyloid hymenial gel and thalli with deeply cross-hatched surfaces and ultimately produces elevated lecideine apothecia that are reddish-brown or black with carbonized epihymenial accretions ( Magnusson 1952; Knudsen et al. 2023 a). Acarospora bolleana has hemiamyloid hymenial gel like A. alba but differs in having a thallus of scattered white areoles becoming solitary lecideine apothecia. while A. alba has a continuous unstratified white thallus with immersed or emergent black apothecia.

Figures

Figure 2. Acarospora alba, Knudsen 13181 Isotype A chasmolithic thallus and young apotecia B apothecia one per areole with thin white margin (Holotype). Scale bars: 500 μm (A, B).