Heterodermia exuberans J. Watts, E. Tripp, and 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 : 73-75

Heterodermia exuberans J. Watts, E. Tripp, and Raynor sp. nov. ( Fig. 4 )

Mycobank # 858397

Diagnosis:—Thallus foliose, white to cream-colored, K+ yellow, adnate, lacking a lower cortex, irregularly orbicular, growing on rocks. Distinct from its close relative, Heterodermia squamulosa , in its production of abundant and morphologically variable reproductive propagules ranging from soredia, these sometimes, with age, developing a cortex, to phyllidia. Other species produce phyllidia which can disintegrate into soredia, but Heterodermia exuberans is unique in producing both soredia and phyllidia concomitantly.

TYPE:— USA, Colorado, Jefferson Co., Pike National Forest, northeast face of Green Mountain , 39° 19’ 11.71” N, 105° 17’ 52.33” W, 2624 m elevation, abundant at base of large granitic cliff in north-facing mixed montane conifer forest, 23 May 2024, J. Watts 1659 (holotype, COLO!; isotype, NY!) .

Description:—Thallus foliose, orbicular to irregular, becoming quite large (up to 12 cm in diameter), adnate. Thallus tightly adnate centrally, peripheral lobes loosely adnate; sometimes forming vertical tiers of decumbent/ascending lobes. Lobes radiating, irregularly to ± sympodially branched, broad ([0.8–]–1–2.5–[–3] mm across), flat to undulate, rarely imbricate. Lobe apices crenate to incised, expanded, and downturned. Upper surfaces dull, cream-colored to light grey, sometimes light brown from light exposure or light blue in apical regions. Weak, round to irregularly elongate maculae often present. Lobe tips occasionally lightly pruinose. Upper cortices prosoplectenchymatous, of uneven thickness, (40–)50–105(–137) µm thick. Asexual lichenized propagules abundant and morphologically variable, ranging (on a single thallus) from soredia to isidioid soredia to dorsiventral phyllidia; primarily borne on underside of upturned lobe tips, also borne along lobe margins and laminal surfaces in occasional clusters, especially on older parts of the thallus. Large phyllidia dorsiventral and densely branched, erect and imbricate, sometimes entirely obscuring the center of the thallus, never breaking down into soredia. Algal layer uneven and discontinuous, (25–)35–55 µm thick. Algae trebouxoid, spherical, 10–15 µm in diameter. Medulla white, (60–)75–105 µm thick, amyloid (I+ violet). Lower surfaces arachnoid, dull, marginally white and becoming ±canaliculate, dark purple or yellowish-brown centrally, rhizinate. Rhizines at first simple and marginal, white to light brown, later becoming black, squarrose, and confluent, obscuring the lower surface centrally. Lower cortices absent from margins, centrally developing a pseudocortex of ±darkened, ±conglutinated medullary cells, often impregnated with debris. Apothecia rare, when present, lecanorine, sessile to substipitate, constricted at the base, to 4 mm in diameter. Thalline margins at first smooth, becoming phyllidiate and finally sorediate. Disks concave, dark brown, epruinose. Asci narrowly clavate, 30–35 × 90–100 µm at maturity; slow to develop and containing hyaline, immature spores in young apothecia, 8-spored. Ascospores brown, two-celled, Pachysporaria-type, lumina rounded-angular, septa dark pigmented, lateral and apical walls thickened. (30–)32–37(–41) × (14–)15–17 µm (n = 10). Epihymenium brown to reddish brown, K-, 15–29 µm thick, pigment inside and between paraphyses apices. Hymenium hyaline, 78–105 µm thick, I+ blue. Paraphyses simple, unbranched, cylindrical, 2.5–3.5 µm thick at apex. Hypothecium hyaline, 80–105 µm, thickest centrally. Proper exciples 22–35µm, dark brown, appearing black in thick section. Thalline margins 115–200 µm thick apically, corticate, cortex 26–146 µm thick. Pycnidia infrequent, 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), zeorin (major), unknown terpene (subordinate and close to norstictic acid in solvent C, acid spray brown, aging purple, longwave UV orange), ± unknown fatty acid (same rf value as unknown terpene), ± leucotylin (minor).

Substrate and Ecology:—Saxicolous and muscicolous on vertical to overhung, 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 ~ 8500 ft. where it often forms extensive colonies, likely from asexual reproduction. One specimen known from bark (S. Shushan s.n., COLO-S5948)

World distribution:—Common to infrequent in the mesic canyons and north-facing upper montane habitats of the Front Range of the southern Rocky Mountains with disjunct collections from upper montane-subalpine forests of Arizona.

Etymology:—The epithet ‘ exuberans ’ is derived from the latin word for exuberant, describing its “effusive and uninhibited” production of asexual lichenized propagules in great abundance. These propagules are often so lavishly abundant as to obscure the thallus in older parts. We additionally chose this name for the way it makes the authors feel overflowing with joy to see healthy populations of this attractive lichen abounding in rich habitats where many other mysteries may also be found, if one looks closely.

Conservation Assessment: — Heterodermia exuberans is preliminarily assessed as Endangered based on IUCN criterion D, as fewer than 250 mature individuals are estimated to occur in the wild. We are so far aware of 25 historical and 35 modern (total 60) specimens attributable to H. exuberans . At ~50% of the localities visited by the authors, one mature individual was observed; at the other 50%, two mature individuals were observed. Doubling the estimate due to the overlooked nature of the organism, we estimate a total population size of ~180 individuals.

Notes:— Heterodermia exuberans is characterized by its diverse reproductive propagules, these fluidly developing and ranging in definition from soredia to isidioid soredia to finally dorsiventral phyllidia, a depsidone deficient chemistry, peripherally white, ecorticate lower surface, and saxicolous habit. In North America, it is most likely confused with its close relative, H. squamulosa , a corticolous species of the southern Appalachians, but this species can be differentiated by its corticolous habit and strictly marginal, strongly upturned phyllidia, these only occasionally disintegrating into soredia ( Lendemer 2009). Heterodermia violostriata Elix (2011: 16) is a rare, corticolous species of Thailand and Australia that also has marginal and laminal phyllidia and a K+ yellow cortex and medulla but differs in its greyish-violet streaked lower surface (similar pigments more continuous across the lower surface in H. exuberans ) and larger spores with sporoblastidia. Heterodermia microphylla (Kurok. 1959: 123) Skorepa in Swinscow & Krog (1976: 139), a pantropical phyllidiate species, exhibits a similar propagule diversity to H. exuberans ; however, in H. microphylla , propagules begin as distinctly corticate, dorsiventral phyllidia, only later becoming strongly dissected and disintegrating into soredia. Heterodermia appendiculata is supported as the closest relative to H. exuberans but differs primarily by its production of the depsidones norstictic and connorstictic acid.

Likely because of its diversity of propagules, many specimens of this new species were found in the COLO herbarium, misidentified as Heterodermia casarettiana , H. japonica , or H. obscurata . These species are superficially similar in overall appearance to H. exuberans owing to their marginal soredia borne on the undersurface of upturned lobes, but differ ecologically, morphologically, and chemically. Heterodermia casarettiana differs by the (usual) presence of norstictic acid in the medulla, true soredia rather than phyllidia, primarily corticolous habit, and patches of pigment on the undersurface. In regard to the name H. casarettiana , there is some confusion about the distribution of pigments on the lower surface, and whether any differences in pigmentation distribution constitutes the designation of a new species. Because of this, Lendemer (2009) referred to eastern NA material of this species as H. casarettiana auct. Amer.; further investigation is required in this potential species complex. Another species that H. exuberans was often misidentified as in COLO is Heterodermia japonica , which differs by the presence of japonene, a continuous algal layer, and lack of phyllidia; however, in an unpublished correspondence (10 Dec. 1956) between William Weber and John Thomson, Thomson considered a specimen (S5948; COLO) of H. exuberans to be a phyllidiate form of H. japonica . Finally, Heterodermia obscurata differs by having strictly soredia, a corticolous habit, and K+ pigments on the lower surface. We expect further annotation of western North American material to fill out and/or expand the known biogeographic range of H. exuberans .

Selected Specimens Examined:— UNITED STATES. Arizona: Apache Co., West side of Escudilla Mountain, 2987 m, 33.916996, -109.111660, 21 May 1974, T. Nash 10724, (COLO-L62125). Coconino Co., West side of San Franciso Peaks, 2682 m, 35.324977, -111.711751, 14 July 1973, T. Nash 7510, (COLO-L58147). Cochise Co., Trail from Rustler’s Park to Fly’s Peak, 2772 m, 31.878293, -109.288749, 18April 1957, W.Weber & S. Shushan s.n., (COLOS8867). Colorado: Boulder Co., Boulder Canyon, Boulder Bowl, 2333 m, 39.998895, -105.410657, 20 October 2024, J. Watts et al. 2848, (COLO). Custer Co., Hardscrabble Creek, Wet Mountains, 2455 m, 38.171836, -105.175683, 14 May 1988, W. Weber & R. Wittman s.n., (COLO-L83545). Douglas Co., Missouri Creek, Pike National Forest, 2315 m, 39.13572, -105.10175, 24 May 2024, J. Watts 1696, (COLO). Hinsdale Co., Cebolla Creek Campground, 2865 m, 38.045902, -107.099837, 29 July 1964, W. Weber s.n., (COLO-L38440). Huerfano Co., South of La Veta along Huajatolla Creek, 2682 m, 37.360146, -105.108568, 17 August 1955, S. Shushan s.n., (COLO-S5948). Larimer Co., The Crags area of Twin Sisters Peaks, Arapaho National Forest, 2933 m, 40.306546, -105.5249361, 1 June 2024, J. Watts & Edie Clark 1778, (COLO). Mineral Co., Big Meadows Road just above South Fork of the Rio Grande, 2737 m, 37.54997, -106.78256, 16 May 2024, J. Watts, E. Manzitto-Tripp, & S. Raynor 1625, (COLO). Park Co., 11.3 mi east of Jefferson, on road to Lost Creek Wilderness, 3048 m, 39.280512, -105.518077, 3 July 1955, S. Shushan s.n., (COLO-S5712). Teller Co., North-west face of Mitre Peak just above Wilson Creek, 2082 m, 38.648993, -105.215838, 4 May 2024, J. Watts & S. Raynor 1338, (COLO). New Mexico: San Miguel Co., Gallinas Canyon NW of Las Vegas, 2300 m, 35.718697, -105.424593, 7 October 1973, W. Weber & G. Kunkel s.n., (COLO- L57913 ).

New Combination:—Below, we provide a new combination for a taxon that has not yet been treated in Heterodermia .

Figures

FIGURE 4. Morphology of Heterodermia exuberans sp. nov. A–C.) In situ macro morphology of the thallus. D–E.) Diverse asexual propagules, soredia and phyllidia. F.) Lower surface of thallus. G.) Thallus cross section under LM. H.) Apothecia with entirely sorediate margins. I.) Asci showing Pachysporaria-type spores. Scale bars: A–C = 10 mm, D = 0.5 mm, E = 1.75 mm, F = 2.75 mm, G = 175 µm, H = 3 mm, I = 35 µm.