Arthonia
Crust lichens having green algae (trebouxioid or trentepohlioid), or unlichenized; thallus smooth, areolate, granular, lacking, immersed or, rarely, squamulose; apothecia round, oblong, linear, or branching or stellate, usually lacking a rim, the fertile disc reaching the margins of the apothecium, a few species with a well-developed excipuloid rim, others with thalline material around the margins resembling a thalline rim; paraphyses embedded in gel, gnarled, mostly branched, sometimes anastomosing; hymenium and hypothecium with a wide variety of pigments, mostly of brown, olive or grey colours; asci broadly clavate to balloon-shaped, with a thin tholus and broad ocular chamber, IKI- or + blue, greenish-blue or grey, often with two small blue dots or lines on either side of the ocular chamber; spores 8 per ascus, colourless, brown or grey, ovate to acicular, but almost always with the broadest point off centre; always septate, with 1 to many septae, some species with both longitudinal and transverse septae; a very large genus that is poorly known in most regions.
References: Clauzade & Roux 1985; Sundin & Tehler 1998; Foucard 2001; Spribille 2006; Grube 2007.
| 1a. | Spores muriform; asci subglobose; apothecia lirelloid …2 |
| 2a. | Thallus a thin green film; apothecia seldom branching; spores 22-34 × 10-15 µ, with 1-2 ranks of length-wise septa visible in side view, lacking a perispore; rare, to be sought in rainforests …[Arthonia obscurum Björk ined.] |
| 2b. | Thallus white, scurfy; apothecia often branching; spores 24-39 × 7.5-15 µ, with 1-3 ranks of length-wise septa visible in side view, with a gelatinous perispore visible in water or K; locally common, especially in dry, open forest …Arthonia xerophilum ined. |
| 1b. | Spores with only transverse septae; asci mostly broadly obovate; apothecia rounded, polygonal or lirelloid …3 |
| 3a. | Upper hymenium K+ red or purple; thallus containing Trentepohlia …4 |
| 4a. | Upper hymenium K+ weakly red-purple; old spores colourless and lacking papillae, 7-11 × 3-5 µ; to be sought in humid forests …[Arthonia spadicea Leighton] |
| 4b. | Upper hymenium K+ strongly red-purple; old spores reddish brown, minutely papillate, mostly larger than in 4a …5 |
| 5a. | Apothecia round to polygonal, constricted at the base, often becoming shortly lobed at maturity; spores with one cell obvious longer and wider, 9-18 × 3.5-8 µ; rare …Arthonia didyma |
| 5b. | Apothecia mostly elliptical, adnate, not lobed; spores with cells of roughly equal size, or one wider, 10-15 × 3-6 µ; to be sought …[Arthonia vinosa Leighton] |
| 3b. | Upper hymenium K-, or K+ drab colours; algae various …6 |
| 6a. | Spores consistently 1-septate …7 |
| 7a. | Apothecia with a well defined rim, formed of a distinct excipuloid region of carbonized hyphae; spores 11-17 × 5-7 µ; alga Trentepohlia; to be sought in humid areas …[Arthonia excipienda (Nyl.) Leighton] |
| 7b. | Apothecia without a well defined rim, lacking any distinct excipuloid material; spores and algae various …8 |
| 8a. | Alga Trentepohlia, usually abundant and easily observed …9 |
| 9a. | Apothecia mostly at least 2 × longer than wide, distinctly snaking and branching; thallus white or grey; spores 10-21 × 3-7.5 µ; rare …Arthonia dispersa |
| 9b. | Apothecia remaining round to elliptical or polygonal, not snaking or branching; thallus orange or dark green; spores 7-11 × 3-5 µ; to be sought in wet forests …[Arthonia spadicea Leighton] |
| 8b. | Alga trebouxioid, often scarce, or lacking algae …10 |
| 10a. | Apothecia distinctly lirelloid, snaking and often branching; thallus whitish, scurfy; spores 14-19 × 6-9 µ …Arthonia memorialis ined. |
| 10b. | Apothecia round to polygonal, not snaking and only rarely branching; thallus various; spores up to 16 µ long and 6.5 µ wide …11 |
| 11a. | Thallus white and scurfy, lacking a cortex, usually surficial and conspicuous, or immersed and producing a conspicuous white stain in the substrate …12 |
| 12a. | Apothecia round in outline; spores 9-15 × 3-5 µ; growing on bark of Populus tremuloides, rarely P. trichocarpa or Salix or in the dripzones of these, generally not where rain-sheltered; rare …Arthonia patellulata |
| 12b. | Apothecia elliptical or polygonal, often with pointed ends; spores 7-15.5 × 2.5-6 µ; on bark of conifers, especially where rain-sheltered, usually on the lower surfaces of branches or on trunks, especially common on Picea, common …Arthonia edgewoodensis ined. |
| 11b. | Thallus grey, brown, green or yellow-green, smooth or granular to verruculose, often with a well formed cortex, usually inconspicuous …13 |
| 13a. | Thallus granular to verruculose; apothecia sphaerical or high-convex, distinctly higher than the thallus …14 |
| 14a. | Thallus mostly pale green or grey; apothecia 0.05-0.25 mm wide; hymenium 20-40 µ high, the gel IKI- or very pale blue; spores 8-15 (‑19) × 2.5-5.5 µ, not or only weakly constricted at the septum, one cell usually distinctly broader; mostly growing on fine twigs, leaves, or moss; common …Arthonia muscigena |
| 14b. | Thallus mostly brown; apothecia 0.15-0.4 mm wide; hymenium 50-65 µ high, the gel IKI+ deep blue; spores 12-15 × 5-6.5 µ, distinctly constricted at the septum, the cells of roughly equal size; on bark of trunks or large branches …Arthonia ampliata ined. |
| 13b. | Thallus smooth and flat, rarely with a few granules; apothecia flat, scarcely higher than the thallus …15 |
| 15a. | Thallus deep green, with a greasy lustre; hymenium 45-55 µ high; spores often broken at the sharply constricted septum, one or both ends pointed, 10-12.5 × 3-5 µ; growing on decaying bark; to be sought in humid forests …[Arthonia oleacea Björk ined.] |
| 15b. | Thallus grey to whitish, often glossy, but lacking a greasy lustre; hymenium 30-35 µ high; spores not breaking, not or slightly constricted at the septum, rounded at the ends, 6-16 × 3-6 µ; usually on living bark, especially on ericaceous shrubs; common and widespread, especially on subalpine shrubs …Arthonia apatetica |
| 6b. | Spores mostly or all with at least 2 septae …16 |
| 16a. | Spores almost always 2-septate: thallus surficial, white and scurfy, algae lacking or few, trebouxioid; apothecia matte, jet black, convex to subglobose, often forming below the substrate and remaining partly enveloped by it …Arthonia trepida ined. |
| 16b. | Spores mostly or all 3-septate; thallus various; apothecia forming on the thallus surface, not enveloped by thalline material …17 |
| 17a. | Algae trentepohliate; apothecia polygonal and lobed or snaking and branching …18 |
| 18a. | Thallus cortex poorly formed, immersed or scurfy; apothecia scarcely lobed; hypothecium medium to dark brown; spores 10-15 × 3.5-5.5 µ; to be sought in humid forests …[Arthonia arthonioides (Ach.) A.L. Sm. sensu lato] |
| 18b. | Thallus with a well-formed cortex, surficial, waxy; apothecia usually distinctly lobed; hypothecium pale to medium brown; spores 17-25 × 5-7 µ …Arthonia radiata |
| 17b. | Algae trebouxioid; apothecia always round to shortly elliptical, never lobed, snaking or branched …19 |
| 19a. | Thallus whitish, scurfy and thin, the algae sparse or sometimes absent; spores 10-20 × 2.5-4 µ, with distinctly pointed ends; growing on trunks of conifers, especially Picea; occasional …Arthonia piceicola ined. |
| 19b. | Thallus brown or yellow-green, granular or areolate, the algae abundant; spores mostly shorter, with blunt or rounded ends …20 |
| 20a. | Thallus brown or olive brown, consisting of distinctly hard-corticate granules and areoles, lacking soredia; spores distinctly constricted at the septae, (11‑) 13-16.5 (‑18) × 3-5 µ …Arthonia indecora ined. |
| 20b. | Thallus bright yellowish green, granular, lacking areoles, sometimes leprose-sorediate; spores not or very slightly constricted at the septae, 12-15 (‑17) × 3-4 (‑4.5) µ …Arthonia vivida ined. |
Arthonia apatetica (A. Massal.) Th. Fr.
A. exilis misapplied.
A rather inconspicuous crust lichen consisting of a thin or immersed, greyish thallus; apothecia sparse to numerous, 0.1-0.6 mm across; disc black, round to lobed, flat or low-mounded, lacking any rim; asci balloon-shaped, height to width ratio less than 2:1, 8-spored; upper hymenium medium brown; hymenium medium brown, the individual paraphyses difficult to discern; hypothecium pale to light brown; spores peanut shell-shaped or shoe-shaped, colourless, 2-celled, one cell usually slightly larger than the other, 6-16 × 2-6.5 µ.
Reactions: All spot tests negative.
Contents: No known lichen substances.
Habitat: On bark of deciduous shrubs within the winter snowpack. All forested elevations, but especially in the subalpine.
Similar Species: Micarea species can appear outwardly similar, but have domed, not flat apothecia, and club-shaped, not balloon-shaped asci.
Specimens: Björk 12882, 13182; Goward 01-199, 96-838.
Local Status: Common.
References: Fink (1935); Foucard (2001).
Notes: The local material is highly variable and may represent more than one species. Further study is needed.
Arthonia ampliata Björk ined.
Thallus granular, areolate to verruculose, whitish, green or olive-gray or (mostly) chocolate-brown, sometimes indistinct, often appearing gelatinous when wet; apothecia low-convex to subspherical, often translucent dark reddish-brown, but mostly opaque blackish brown, 0.15-0.4 mm wide; hymenium 50-65 µ high, K- or K+ yellowish or olive, the gel IKI+ royal blue, the upper portions reddish brown or dark brown, K+ less reddish or gaining a slight olive tone; hypothecium light to medium reddish brown, K- or K+ less reddish or gaining a slight olive tone; spores 13-15 × 5-6.5 µ, usually halonate, usually distinctly constricted at the crosswall, the cells of roughly equal sizes.
Reactions: Spot tests all negative.
Contents: Unknown, but probably lacking identifiable lichen substances.
Habitat: Bark of conifers, Alnus or Acer, usually in dripzones, also within the rain-shelter of much branched Picea. Middle to upper forested elevations.
Similar Species: Differs from Arthonia muscigena in the larger apothecia, the higher hymenium and wider spores. Can be confused with Arthonia laevigata, but always produces a granular thallus and has spores with a strong constriction at the crosswall.
Specimens: Björk 12894.
Local Status: Rare.
Notes: Known only from inland BC and northern Idaho.
Arthonia didyma Körber
Thallus immersed in the substrate or thin and surficial, olive green or pale brownish, sometimes pinkish, containing trentepohlioid algae; apothecia rounded or polygonal, distinctly convex, sometimes constricted at the base; hymenium 35-50 µ high, with red-brown pigment throughout; hypothecium pigmented like the hymenium; spores 14-17 × 4.7-7 µ.
Reactions: Spot tests all negative.
Contents: No lichens substances known.
Habitat: On wood in humid, low-elevation forests.
Similar Species: Arthonia vinosa is similar but has flatter apothecia
Specimens: Goward 96-1163.
Local Status: Rare.
Arthonia dispersa (Schrad.) Nyl.
Thallus thin and smooth, grey or whitish, containing trentepohlioid algae; apothecia snaking and often densely branching, often asterisk-shaped, scarcely raised above the thallus, lacking a rim, disc fully exposed, the lobes ; hymenium 30-40 µ, colourless, K-, IKI + light to medium blue; upper hymenium dark brown, K- or K+ olive; spores with a single septum, ovate, not or slightly constricted at the septum 14-21 × 4-7.5 µ; occasional in coastal and humid inland regions, often on smooth bark of Betula or Alnus.
Reactions: Spot tests all negative.
Contents: No lichen substances known.
Habitat: On smooth bark of Betula and Alnus near lake and river shorelines. Lower elevations.
Similar Species: Arthonia excipienda is generally similar, but has a conspicuous rim around the disc. Arthonia radiata may appear similar but has 3-septate spores.
Specimens: Björk 9832.
Local Status: Rare.
Arthonia edgewoodensis Björk ined.
Thallus an often extensive whitish stain, immersed in bark or on dead leaves, with clusters of algae visible macroscopically as green blemishes; apothecia matte, jet black or dark brown, round to triangular or shortly snaking, flat to moderately convex, often developing below the substrate and bursting through it; hymenium 25-30 µ, colourless, K- or K+ yellowish, IKI+ pale greyish blue in the gel, dark brown in upper portions, K- or K+ faintly olive; hypothecium light brown, K- or K+ faintly olive, IKI+ pale greyish blue; paraphyses dense, about 1.5 µ wide, richly branched and anastomosed, with a capitate dark brown apex swollen 4-8 µ wide; asci about twice as high as wide, IKI- except faintly greyish blue in the region above the lumen and ocular chamber; spores halonate, narrowly ovate to (occasionally) elliptical or oblong, 1-septate, the outer wall often constricted at the crosswall, one cell usually longer and broader and the other, 7-15.5 × 2.5-6 µ.
Reactions: All spot tests negative.
Contents: Unknown.
Habitat: Picea bark, especially common on undersides of branches, rarely on Pseudotsuga or Salix. Lower to middle elevations.
Similar Species: Similar to Arthonia punctiformis (unknown from the study area), but with 1-septate spores, and without the mostly rounde apothecia characteristic of that species. SPECIMENS: Björk 12224, 13228, 14286.
Local Status: Very common.
Notes: Widespread in the western boreal forests of North America, south to northern temperate zones.
Arthonia indecora Björk ined.
Thallus brown or olive brown, of distinctly hard-corticate granules and areoles, containing trebouxioid algae; apothecia round or elliptical, high-convex or sometimes subspherical, brownish black, matte; hymenium olive-brown in upper portions, K- or + olive-gray; spores 3-septate, distinctly constricted at the septae, (11‑) 13-16.5 (‑18) × 3-5 µ.
Reactions: Spot tests all negative.
Contents: No lichen substances known.
Habitat: Usually on rough bark of conifer branches, less often on trunks or on broad-leaf trees. Lower to middle elevation forests.
Similar Species: Arthonia ampliata can sometimes appear similar, but has 1-septate spores and usually grows on deciduous shrubs.
Specimens: Björk 10745.
Local Status: Uncommon.
Notes: Known only from inland BC and northern Idaho.
Arthonia memorialis Björk ined.
Thallus white, scurfy, containing sparse trebouxioid algae; apothecia black, 0.15-0.35 × 0.15 mm, partly covered in scurfy thalline material, lirelloid, distinctly snaking and occasionally with 1-2 branching lobes, lacking any excipuloid tissue around the disk; hymenium 35-45 µ high, dark olive in upper portions, K- or + yellowish; spores 1-septate, ovate, not constricted at the septum, 14-19 × 6-9 µ.
Reactions: Spot test reactions all negative.
Contents: No lichen substances known.
Habitat: Smooth bark of Populus trichocarpa branches in the canopy; known from only a single collection at the edge of a pasture.
Similar Species: Arthonia xerophilum is very similar in general appearance, but has muriform spores, is almost always on conifers, seemingly never on Populus trichocarpa, and tends to occupy rain-sheltered microsites.
Specimens: Björk 17851.
Local Status: Rare.
Notes: Known only from the study area.
Arthonia muscigena Th. Fr.
Thallus granular, whitish, translucent when wet, often indistinct; apothecia low-convex to subspherical, blackish, 0.05-0.25 mm wide; hymenium 25-40 µ high, K- or K+ yellowish or olive, the gel IKI+ royal blue; upper hymenium pale to medium orangish brown, K- or gaining a slight olive tone; hypothecium colourless, K- or gaining a slight olive tone; paraphyses sparse, distinguishable along their entire lengths (at least as seen in IKI), surrounded by gelatinous sheaths (at least at the apex), lumina about 1 µ wide; asci 2-2.5 × high as wide, with an IKI+ royal blue hazy outer coat and a blue lining of the ocular chamber and often with a dark blue ring shortly above the apex of the ocular chamber (appearing from the side as a pair of dark blue dots); spores 8-12 × 2.5-4 µ, usually halonate, scarcely constricted at the croswall, the cells of unequal sizes.
Reactions: All spot tests negative.
Contents: No known lichen substances.
Habitat: On conifer needles in humid forests, also on decaying polypores on Betula trunks. Lower to middle elevations.
Similar Species: See notes under Arthonia ampliata.
Specimens: Björk 10885.
Local Status: Occasional.
Arthonia patellulata Nyl.
Thallus white, scurfy, often forming large patches (appearance much like Lecania dubitans); apothecia scattered or a few paired, round in outline, matte jet black, often with a light dusting of calcium oxalate over the surface; hypothecium medium brown to blackish brown as seen in thin section; apothecia round, low convex; hymenium 40-60 µ high; spores 9-15 × 3-5 µ, with a single crosswall.
Reactions: All spot tests negative.
Contents: No known lichen substances.
Habitat: On trunks and branches of Populus tremuloides, also on Juniperus scopulorum. Lower to middle elevations.
Similar Species: Arthonia trepida Björk ined. is similar and also grows on Populus, but has very small apothecia consistently with 3-celled spores. Also similar is Lecania dubitans, which differs in having oblong, curved spores with the cells of equal size; it too grows on Populus. See notes under Lecidella patelluloides.
Specimens: Goward 78-857, 80-18-3.
Local Status: Occasional.
Arthonia piceicola Björk ined.
Thallus thin, partly immersed, forming a white stain in the substrate 1-4 cm wide, the immersed portions lacking algae, also with scattered lichenized areoles that quickly disintegrate into abundant surficial granular soredia containing algae, these 25-30 µ wide but grouped into consordia 40-50 µ wide, creamy white, sometimes obscuring the immersed portions; apothecia matte, brownish black, (sub)spheric, distinctly constricted at the base, even when young, sometimes becoming botryoid; hymenium pale to medium brown, dark brown in upper portions, K- or K+ yellowish or slightly greenish; hypothecium dark brown, formed of chaotic hyphae with pigmented walls; spores 3-septate, clavate, acute at the broader end and gradually tapered to the subulate to acuminate narrow end, lacking constrictions, the cells of equal length, or the narrowest cell sometimes longer than the other three, (10‑) 14.6 (‑20.5) × (2.5‑) 3 (‑4) µm.
Reactions: Spot tests all negative.
Contents: No lichen substances known.
Habitat: On rough bark of conifers, especially Picea, in moderately dry to humid mid seral or oldgrowth forests. Lower to middle elevations.
Similar Species: See notes under Arthonia vivida ined.
Specimens: Björk 10744, 12277.
Local Status: Common.
Notes: In principle, A. piceicola might be interpreted as a lichenicolous fungus growing on a sorediate lichen. Two considerations argue against this interpretation: first, the apothecia occur both on algal portions of the thallus and on non-algal portions; and second, the supporting thallus matches no sorediate crust known to us.
Arthonia radiata (Pers.) Ach.
Thallus thin, smooth, grey or whitish, waxy in appearance, sometimes immersed; apothecia branched, usually asterisk-like, usually not raised above the level of the thallus (in our material); hymenium light to medium brown in upper portions, K+ olive-gray; spores 3-septate, ovate to ovate-fusiform, often with constrictions at the septae, 12-25 × 4-7 µ.
Reactions: Spot tests all negative.
Contents: No lichen substances known.
Habitat: On smooth bark of shrubs along shores of large rivers and lakes. Lower to middle elevations.
Similar Species: Arthonia dispersa has 1-septate spores and, usually, narrower apothecial branches.
Specimens: Björk 9798, 12387; Goward 01-201.
Local Status: Uncommon.
Notes: The type of A. radiata differs from western North American material both in having narrower apothecial lobes and in producing a distinct rim of excipuloid material around the disc. Locally we note a partial correlation between thallus colour (gray versus white) on the one hand and spore size, wall thickness and degree of constriction at the septae on the other hand. Further work is needed.
Arthonia trepida Björk ined.
Thallus white and scurfy, algae lacking or a few trebouxioid algae present; apothecia matte jet black, convex to subglobose, with a cover around the margins of scurfy thalline material; hymenium medium to dark reddish brown in upper portions, K+ pure brown, IKI+ medium greyish blue; spores 2-septate, the outer walls slightly constricted at the septae 8-11 × 3.5-4.5 µ.
Reactions: Spot tests all negative.
Contents: No lichen substances known.
Habitat: On smooth bark of Populus tremuloides branches. Currently known only from middle elevations.
Similar Species: Melanomma polita ined. is similar in characters of the thallus and perithecia, though the latter are distinctly glossy when viewed under a dissecting scope.
Specimens: Björk 13226.
Local Status: Rare.
Notes: Known only from the study area.
Arthonia vivida Björk ined.
Thallus dull or bright yellow-green, rarely immersed on punky bark, fully lichenized with a trebouxioid alga, areolate or granular, strongly to weakly corticate, granules becoming soredium-like, often thickly piled up and sometimes becoming leprose, K+ gold; hymenium colourless or pale brown, 20-35 µ high, K- or K+ yellowish, IKI+ light to medium turquoise blue; upper hymenium dark brown, K- or K+ browner or olive; hypothecium colourless to light brown, K+ browner or olive; paraphyses swollen and dark-pigmented at the apex; asci IKI+ with a minute dark blue ring shortly above the lumen apex (appearing from the side as a pair of blue dots); spores 3-septate, elliptical, with the outer wall moderately to strongly constricted at the septae, both ends blunt to rounded, rarely the narrow end acute, the cells of equal lengths, 12-17 × 2.5-5 µ.
Reactions: All spot tests negative.
Contents: Unknown, probably lacking lichen substances.
Habitat: On bark of conifers and shrubs. Lower to middle elevations.
Similar Species: Arthonia piceicola ined. is similar, but has a creamy white rather than bright green thallus. Also, it has pointed rather than blunt spore ends and constricted outer spore walls. Arthonia vivida may key out to A. punctiformis in European floras owing to similarities in the spores. That species, however, has flat apothecia and is unlichenized or only weakly lichenized.
Specimens: Björk 12301.
Local Status: Occasional.
Notes: Known only from inland BC and eastern Washington State.
Arthonia xerophilum Björk ined.
Thallus white, scurfy, covering extensive areas of bark, containing a trebouxioid alga and abundant calcium oxalate crystals; apothecia snaking and most with one or two branches, emerging from within the thallus, remaining partly covered in a whitish pruina of calcium oxalate, the disc breaking into dashes along its length; hymenium 70-80 µ high, K+ yellowish, IKI+ pale greyish blue; upper hymenium medium olive grey, K+ greener, IKI+ medium greyish blue; asci about 65 × 40 µ, IKI+ pale greyish blue with a slightly darker blue field in the lower half of the tholus; spores mostly ovate, the widest point distinctly off centre, 24-37 × 7.5-15 µ, muriform, with 1-3 ranks of length-wise septae as seen from above, with a gelatinous perispore visible in K.
Reactions: All spot tests negative.
Contents: Unknown, but probably lacking any lichen substances.
Habitat: Almost always on trunks of young Pseudotsuga too young to produce fissured bark, yet still rain-sheltered by the upper portions of the canopy. Lower to middle elevations.
Similar Species: Arthonia memorialis is superficially similar, but has spores with exclusively transverse septae. Arthonia radiata has a waxy thallus and asterisk-like apothecia with more numerous radiating branches.
Specimens: Björk 12118, 13941.
Local Status: Common.
Notes: So far known only from central inland BC.