Heterodermia caesiosora J. Watts, E. Tripp, & Raynor, 2025

Watts, Jacob L., Raynor, Seth J. & Manzitto-Tripp, Erin A., 2025, Character evolution in Heterodermia s. l. (Physciaceae; Caliciales) and two new species from the southern Rocky Mountains, USA, Phytotaxa 698 (2), pp. 61-81 : 70-72

Heterodermia caesiosora J. Watts, E. Tripp, & Raynor sp. nov. ( Fig. 3 )

Mycobank # 858396

Diagnosis:—Thallus foliose, irregularly orbicular, of narrow, ±convex, radiating, lobes brown to cream-colored, K+ yellow, adnate, lacking a lower cortex, rhizines brown, often projecting beyond lobe margins, growing on rocks. It is most easily confused with Heterodermia japonica but differs by having narrower lobes, a discontinuous algal layer, and lacking japonene and related terpenes. It is reminiscent of Heterodermia speciosa and H. tremulans because of its bluish, granular soredia in labriform soralia, but lacking a lower cortex and having narrower lobes. It is distinct from H. chilensis (Kurok. 1962: 65) Swinscow & Krog (1976: 115) by its adnate growth form, dense rhizines, expanded and incised lobe apices, and lack of distinctly thickened, corticate margins of the lobe undersurface.

TYPE:— USA, Colorado, Park Co., Eleven Mile Canyon Recreation Area . 38° 57’ 58.98” N, 105° 22’ 14.59” W, 2486 m elevation, on sloping boulders in a steep canyon forest dominated by Pseudotsuga menziesii , 22 August 2024, J. Watts 2552 (holotype, COLO!; isotype, NY!) .

Description:—Thallus foliose, orbicular to irregular, often small (~2.5–5[–8] cm in diameter), adnate. Lobes radiating, irregularly to ± sympodially branched, narrow ([0.5]– 0.7–1.1 mm broad), convex to flat, or rarely undulate, contiguous to imbricate. Lobe apices expanded (to 1.3–1.6 mm) and incised to radially branching. Upper surfaces dull, cream-colored to light grey, but often brown pigmented from light exposure. Maculae rarely present in low light. Lobe apices pruinose, rarely epruinose in low light. Upper cortices prosoplectenchymatous, of uneven thickness, (12–)25–75(–130) µm thick. Asexual lichenized propagules coarse soredia (45–65 µm in diameter) borne primarily on secondary lobes in terminal, ±labriform soralia, variable depending on the light environment; in low light, developing large, typical labriform soralia on undersurface of greatly expanded lobe apices, in high light, developing terminal small, ±labriform soralia with dark greyish-blue pigmented, coarsely granular soredia and the occasional small, laminal, round soralium in older parts.Algal layer discontinuous, interrupted by cortical intrusions, (25–)55–95(–120) µm thick.Algae trebouxoid, spherical, 10–16 µm in diameter. Medulla white, 67–205 µm thick, non-amyloid (I-). Lower surfaces arachnoid, dull, marginally white, becoming light brown centrally, developing a pseudocortex, rhizinate. Rhizines dense, marginal and often projecting beyond the lobe margin, concolorous with the thallus or brown, rarely becoming black, simple to irregularly branched, 1–2(–3) mm long, partially obscuring the lower surface centrally. Lower cortices absent from lobe apices, centrally developing a pseudocortex of ±conglutenated medullary cells, often impregnated with debris. Apothecia rare, only known from the type specimen; when present, lecanorine, sessile to substipitate, constricted at the base, to 1.5 mm in diameter. Thalline margins at first smooth, becoming partially sorediate. Disks brown, concave, epruinose. Asci narrowly clavate, 45–57 × 13–17 µm, 8-spored. Ascospores brown, two-celled, Physcia-type, lumina angular, septa dark pigmented, apical walls thickened, one cell often larger than the other. (7–)8–12 × (16–)18–24 µm (n=10). Epihymenium brown to reddish brown, K-, 3–9 µm thick, pigment inside and between paraphyses apices. Hymenium hyaline, 50–65 µm thick, I+ blue. Paraphyses simple, unbranched, cylindrical, 2.5–3.5 µm thick at apex. Hypothecium hyaline, 25–65 µm thick. Proper exciples 12–25 µm thick, hyaline. Thalline margins 100–150 µm thick apically, corticate, cortex thicker basally, 30–150 µm thick. Pycnidia rare, immersed. Ostioles light brown to black. Conidia bacilliform, 3–5 × 1 µm.

Spot tests:—Cortex, medulla, and lower surface: K+ yellow, C-, KC- (remaining yellow), P- or P+ pastel yellow. Lower surface pigment K-.

Secondary Metabolites:—Atranorin (major) and zeorin (major), and rarely salazinic acid (trace).

Substrate and Ecology:—Saxicolous and muscicolous on vertical to sloping, usually mossy and mesic to semimesic rock faces in montane to lower subalpine forests between ~ 6000 ft. and ~ 10,500 ft. Most abundant on north-facing slopes just above rivers and cliff bases at ~ 8500 ft. elevation. One specimen known from bark (W. Weber & L. Viereck s.n., COLO–S7181).

World distribution:—Infrequent to rare in the southern Rocky Mountains of Colorado with a disjunct locality in Alaska suggesting a much broader distribution, perhaps throughout the northern Rocky Mountains as well.

Etymology:—The epithet ‘ caesiosora ’ refers to the bluish grey soredia of the species.

Conservation Assessment: — Heterodermia caesiosora is preliminarily assessed as Critically Endangered (CR) based on IUCN criterion D, as fewer than 50 mature individuals are estimated to occur in the wild. We are so far aware of 7 historical and 13 modern (total 20) specimens that can be attributed to H. caesiosora . In all modern collections made by the authors, only one mature individual was observed; however, we expect the species to be overlooked/ undercollected are thereby double our estimate of the number of mature individuals to 40.

Notes:— Heterodermia caesiosora is characterized by its narrow, ± convex, K+ yellow lobes that are adnate and lack a lower cortex, its bluish grey labriform soralia terminal on secondary lobes, its brown rhizines which often project beyond the lobe margins, and its small spores. Heterodermia japonica , a pantropical species, is similar in its lack of lower cortex and labriform soralia but that species has black, ±squarrose rhizines that are never visible from above, a continuous algal layer and uniformly thick upper cortex, and japonene and related terpenes. Heterodermia chilensis , a species of coastal Chile, has labriform soralia and an interrupted algal layer, but this species exhibits lobes that are marginally discrete and dichotomously branching, the apices of which are entire, not incised as in H. caesiosora . Heterodermoa galactophylla (Tuck. 1848: 224) W.L. Culb. (1967: 482) differs by its subascending lobe apices which bear labriform soralia; most primary lobe apices of H. caesiosora are esorediate, the soralia concentrated to secondary lobes. Heterodermia hypocaesia (Yasuda in Räsänen 1940: 139) D.D. Awasthi (1973: 113), a primarily southern hemisphere species, also lacks a lower cortex but has upturned, labriform soralia but differs in its yellowish lower surface, the regular presence of salazinic acid in high concentrations, and much larger ascospores.

A few specimens of Heterodermia caesiosora were discovered in the COLO herbarium misidentified as H. speciosa and H. tremulans , both of which are superficially similar but are distinctly corticate underneath. Heterodermia caesiosora is additionally separated from these species by its discontinuous algal layer and smaller spores—these smaller than most species of Heterodermia . This misidentification is likely due to historical confusion surrounding the differences between cortex and pseudocortex. We expect further annotation of specimens from western NA will uncover more populations of H. caesiosora . Close examination of specimens in this complex from eastern NA may reveal further diversity in the group as the two treatments of Heterodermia for this area disagree on the identity of NA material as either H. tremulans ( Culberson 1966) , or H. speciosa ( Lendemer 2009) and note extensive variation in the degree of development in the lower cortex ( Lendemer 2009).

Selected Specimens Examined:— UNITED STATES. Alaska: Denali Boro., McKinley River, Denali National Park and Preserve, 548 m, 63.4167, -150.917, 1 August 1956, W. Weber & L. Viereck s.n., (COLO-S7181). Colorado: Boulder Co., Bear Peak, Boulder Open Space and Mountain Parks, 2415 m, 39.962453, -105.295841, 19 October 2023, J. Watts 768, (COLO). Eagle Co., Homeskate Creek, Holy Cross Wilderness, 2893 m, 39.387005, -106.451006, 16 July 2024, J. Watts 2240, (COLO). Hinsdale Co., Vallecito Creek, 2741 m, 37.56836, -107.521687, 26 November 1977, R. Rosentreter CO-29, (COLO-L95045). Jefferson Co., Northeast face of Green Mountain, Pike National Forest, 2624 m, 23 May 2024, J. Watts 1663, (COLO). Larimer Co., Dadd Gulch Trail just south of Cache la Poudre River, Roosevelt National Forest, 2499 m, 40.67759, -105.558456, 11 May 2024, J. Watts 1423, (COLO). Pitkin Co., Lost Man Campground, Roaring Fork River, 3217 m, 39.119651, -106.624281, 30 July 2024, J. Watts & Ella Henry 2449, (COLO). Teller Co., Raspberry Mountain, Pike National Forest, 3076 m, 38.885809, -105.127882, 5 May 2024, J. Watts & S. Raynor 1392, (COLO).

Figures

FIGURE 3. Morphology of Heterodermia caesiosora sp. nov. A–D.) In situ macro morphology of the thallus. E.) Upturned soralia on secondary lobes bearing bluish grey soredia. F.) Lower surface of thallus. G. Thallus cross section under LM. H.) Apothecia with partially sorediate margins. I. Asci showing Physcia-type spores. Scale bars: A–C = 8 mm, D = 10 mm, E = 1.5 mm, F = 2 mm, G = 200 µm, H = 1 mm, I = 20 µm.