Acarospora oscurensis K. Knudsen, Kocour. & Kondrysová, 2025

Acarospora oscurensis K. Knudsen, Kocour. & Kondrysová sp. nov.

Fig. 6 View Figure 6

Type.

U. S. A. • New Mexico, Lincoln Co., Tularosa Basin, Oscura, Road 54 , 33.4863, -106.0928, alt. 1475 m, SW-NE crest above the valley, southernmost hill, on soft acid sandstone, 14. Mar. 2022, K. Knudsen 19438 & J. Kocourková (SBBG-holotype) GoogleMaps .

Diagnosis.

Similar to Acarospora austrooccidentalis with a high hymenium, differing in having globose to broadly ellipsoid ascospores (1 –) 2–3 (– 6) × 1.0–3.4 µm vs. ellipsoid ascospores (1.5 –) 4.0–4.6 (– 5.1) × (1.0 –) 2.0 (– 2.8), thicker paraphyses (1.5 –) 2.0–2.5 (– 3.5) µm vs. 1.0–1.5 (– 2.0) µm, in occasionally producing white stromata, and with young apothecia often having in early development a smooth margin and lacking epihymenial accretions.

Etymology.

Named for Oscura in the Tularosa Basin of the Chihuahuan Desert in New Mexico, where we first collected this species.

Description.

Thallus endolithic up to 0.2 mm deep, up to 5 cm wide, algal cells ca. 5–10 µm wide, algal layer variable, continuous below and between apothecia, the sandstone often spongy when wet to the touch, or discontinuous deep in substrate. Apothecia round to irregular, 0.3–1.3 mm wide, 0.4–0.5 mm tall, sometimes elevated on white mycelial base or emerging from white stromata. Margin thick, 100–250 µm wide, outer layer carbonized, inner layer reddish to hyaline, widths variable, hyphae 1–2 µm wide, rim smooth when young, slightly elevated above the disc, becoming segmented. Disc reddish-brown to black, at first usually without epihymenial accretions, then developing an umbo or several small dots of melanin, eventually dense and sometimes gyrose, excluding the margin. Hymenium (100 –) 120–150 (– 180) µm tall, epihymenium uneven (10 –) 20–30 µm tall, paraphyses (1.5 –) 2.0–2.5 (– 3.5) µm wide, branched and anastomosed, apices expanded to 4.5 µm with black pigment mark, hymenial gel IKI + light blue, turning red in squash, hemiamyloid. Asci 120–160 × 10–30 µm, often cylindrical, rarely becoming inflated, ascospores usually broadly ellipsoid, sometimes with small globose ascospores (1 –) 2–3 (– 6) × 1.0–3.4 µm, variable (n = 40), oil drops absent or one large oil drop, sometimes a second smaller one. Subhymenium up to 30 µm tall, IKI + blue. Hypothecium 20–30 µm tall, with hyphae 1–2 µm thick, continuous with margin. Occasionally with white stromata 100–300 µm wide, a black dot often on top and some scattered algae cells in a thalline wall around pycnidia. Pycnidia up to 200 µm across with long, thick conidiogenous cells 30 × 3 µm, producing abundant conidia 2–3 × 1 µm. Eventually producing a single apothecium from each stroma. Not producing secondary metabolites.

Habitat and distribution.

On acid and calciferous sandstone and volcanic ash in Arizona, Colorado, Nevada, New Mexico, and Utah.

Additional specimens examined.

U. S. A. • Arizona, Maricopa Co., Sierra Estrella Regional Park, Corgett Wash , 33.2833, -112.3333, alt. 850 m, 20 Oct. 1974, T. H. Nash III ( ASU) GoogleMaps ; • Colorado, Garfield Co., Flat Tops Wilderness, forested area just above Crater Lake , 39.8166, -107.4166, alt. 3140 m, on siliceous rocks, 24 June 1992, T. H. Nash III 31921 ( ASU) GoogleMaps ; • Nevada, Lincoln. Co., Rainbow Canyon, large volcanic ash formation , 37.4959, -114.5827, alt. 1240 m, on sunny rhyolite ash, 13 Aug. 2019, Hollinger 23226 a ( BRY-L-0052277 ) GoogleMaps ; • New Mexico, Lincoln Co., Tularosa Basin, Oscura , 33.4863, -106.0928, alt. 1475 m, SW-NE crest above the valley, southernmost hill, on soft acid sandstone, 14 March 2022, J. Kocourková 10795 ( 3 specimens, hb. K & K, SBBG) GoogleMaps ; • 14 March 2022, J. Kocourková 10797 ( 2 specimens, hb. K & K, BYU), 10852 ( 2 specimens, hb. K & K, PRM) GoogleMaps ; • Utah, Emery Co., 39.0945 -110.7392, alt. 1621 m, in the “ Little Grand Canyon ” of San Rafael River , south side of San Rafael River near sandstone butte above river on hard sandstone, 28 April 2023, S. Leavitt et al. 23124, 23126, 23129 ( BRY-C) GoogleMaps ; • 38.6839 -110.1695, alt. 1405 m, 15 April 2023, S. Leavitt et al. 23028, 23034 ( BRY-C) GoogleMaps ; • San Rafael Desert, vicinity of Three Canyons overlook, on sandstone on rim west of the Green River , 38.7087, -110.1245, alt. 1320, 15 Apr. 2023, S. Leavitt et al. 23077 ( BRY-C) GoogleMaps ; • San Juan Co., Bears Ears National Monument, between the UT 211 Rd. and sandstone crest , 37.9836, -109.5003, alt. 1869 m, thin juniper and shrubby pine vegetation on gently sloping area, on sandstone rocks, 22 Sept. 2024, J. Kocourková 11560 & K. Knudsen (hb. K & K), Knudsen 19532 & J. Kocourková ( SBBG) GoogleMaps ; • La Sal Mts., La Sal Loop Rd, top of small SW oriented crest , alt. 1866 m, 38.4532, -109.3750, on HCl – sandstone, 21 Sept. 2024, J. Kocourková 11512, 11556 & K. Knudsen (hb. K & K) GoogleMaps ; • Wayne Co., Capital Reef National Park, Cassidy Arch Trail , 38.2637, -111.2159, no alt., on Navajo sandstone, 12 June 1992, Larry St. Clair 14030 ( BRY-L-0030690 ) GoogleMaps .

Notes.

The high hymenium and broadly ellipsoid ascospores are characteristic of Acarospora oscurensis , as well as the tendency to have thicker paraphyses than A. austrooccidentalis (see also discussion under the latter species).

Acarospora oscurensis , like Sarcogyne similis and S. poeltii , produces stromata that contain pycnidia but which eventually produce apothecia ( Knudsen et al. 2011, picture of stromata of S. similis as the synonym A. reebiae ). It differs from these two species in the stromata being white and not black. As with S. similis and S. poeltii , apothecia may also emerge directly from the endolithic thallus or form by replication by division. So far white stromata are rare in collections examined but common at the type locality. They usually occur when the thallus is continuous between apothecia.

The apothecia of Acarospora oscurensis often do not have a continuous endolithic algal layer between apothecia and are elevated by a white mycelial base (which is not a remnant of stromata) and can have a distinct algal layer directly beneath the hypothecium.

Acarospora oscurensis can be easily determined by its young apothecia initially having a smooth margin and lacking epihymenial accretions on non-calcareous sandstone. But in emergent apothecia in sandstone with a porous top layer of large grains, the apothecia may have already developed an umbo and / or segmenting margin before they are fully emergent.

Acarospora oscurensis can be misdetermined as A. leavittii , which can sometimes have all small, broadly ellipsoid ascospores that are not fully developed to 10 × 7 µm, which are released at any size during good habitat conditions for lichenization. But A. leavittii generally will have longer ascospores (3.5 –) 4.0–5.0 – 7.0 (– 10.0) × (2.0 –) 2.5–3.0 (– 5.0) µm vs. (1 –) 2–3 (– 4) × 1–3 µm and a deeper subhymenium up to 60 µm vs. up to 30 µm tall ( Knudsen et al. 2022).