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Diplotomma epipolium (Ach.) Arnold (redirected from: Rhizocarpon cumulatum)
Family: Rhizocarpaceae
[Buellia alboatra var. epipolia (Ach.) Rostr.,  more]
Diplotomma epipolium image
Stephen Sharnoff  
Life habit: lichenized (mutualistic with algal photobionts) thallus: crustose (crustaceous) – episubstratal – unspecified thallus: continuous, diffuse, effuse | granular, granulose, granulate | cracked, fissured, fractured, rimose | compartimentized – areolate, squamulate [th] upper surface: grey(ish) | white(ish) [th marginal and upper surface] specific structures: absent ascomata: absent | present ascoma: apothecial, apothecioid – hymenial ascoma [mm]: (low) 0.3 (high) 0.8 (max) 1.5 ascoma: immersed, innate | subsessile, subimmersed, adnate, semi-immersed, emergent | sessile, superficial [ascm, if apoth] disc, mazaedium: plane, flat, flattened, expanded | convex [ascm, if apoth] disc, mazaedium: epruinose | pruinose [ascm, if apoth] subhymenial layers, hypothecium; [if perith] basal excipulum: brown(ish) (if pale: fawn, tan; if mid: cinnamon) [ascm] paraphyses/-oids: present [ascm] epihymenium, epithecium: brown(ish) (if pale: fawn, tan; if mid: cinnamon) asci: lecanoralean [asc] tholus: thickened [asc] tholus amyloidity (iodine reaction): present [asc] tholus amyloidity pattern: amyloid with acuate axial body towards the apex (= Bacidia-, Buellia-, Ramalina-types etc) ascospores: (median) 8.0 [asp] shape: ellipsoidal | [cur] – curved, unciform, falcate, sickle-shaped [asp] length [µm]: (low) 14.0 (high) 22.0 (max) 25.0 [asp] width [µm]: (low) 6.0 (high) 10.0 [asp] septa: present [asp] septa: transversely septate | muriformly septate – muriform, submuriform [asp] transversal septa: (min) 1.0 (low) 3.0 (high) 5.0 [asp] pigmentation: reddish brown [asp] perispore, epispore: ornamented, rough, warted, striate, cracked secondary metabolites: absent primary photobiont: present secondary photobionts (eg in cephalodia): absent primary photobiont: chlorophytaceous – trebouxiaceous, chlorococcoid.

substrate: rock – calcareous, calciferous, basic.
Thompson, J., 1997. American Arctic Lichens: The Microlichens.
Thallus chinky-areolate, thick, to 0.7mm thick, continguous and well-defined, chalky white, dull, farinose or not; hypothallus lacking or of a thin white layer. Apothecia black, at first flat, soon convex and almost spherical, in compound heaps, botryose; margin black, pruinose or not, sometimes surrounded by a false thalloid margin; exciple pale above and at sides, lower part under apothecium red-brown; disk pruinose, dull; hypothecium yellowish or pale brownish; epithecium pale olive-green; hymenium 90-100 µm, hyaline; paraphyses 2.5-3.0 µm thick, intricate, not inspersed, not capitate; spores 8, submuriform, 3-septate transversely, center cells 1-septate longitudinally, very soon brown, halonate, 12-14 X 5.5-7.5 µm.

Reactions: medulla K—, C—, P—, I—; hypothecium K— but lower part of exciple K+ purple-brown; epithecium K—; hymenium 1+ blue.

This species grows on shaded calcareous rocks. It is known only from the type material collected on the Pitmegea River, north slope of Alaska.