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Species Information
Summary: Coccomyces dentatum is included as an example of the ascomycete order Rhytismatales. This is the most frequently collected species of Coccomyces. It is common and widespread and in the Pacific Northwest is often found growing on dead leaves of Mahonia spp. (Oregon grape). Fruitbodies up to 0.1cm wide open out as squares, pentagons, or hexagons, often on a paler part of the host that is surrounded by a black line. Each fruitbody has a grayish or grayish yellow spore-bearing surface, a pale margin, and a shiny black exterior. Coccomyces dentatus (Kunze ik Schm. ex Fr.) Sacc. var. hexagonus Penz. & Sacc. is a name applied to large specimens of Coccomyces dentatus with regular, hexagonal apothecia from the western U.S., but studying the type material is problematic. (Sherwood).
Collections were examined from BC, WA, OR, ID, AZ, CA, FL, LA, NC, PA, TN, VA, Panama, Brazil, Colombia, Venezuela, Belgium, Czechoslovakia, France, Germany, Italy, Tunisia, Canary islands, (Sherwood). It occurs also in the United Kingdom (Sherwood).
Fruiting body: Fruitbodies are up to 0.1cm wide, with a translucent gray or grayish yellow spore-bearing surface, "paler margins, and shiny black exteriors". They are immersed in the substrate at first, and then open "as squares or pentagons". The fruitbodies "grow within a paler part of the host, which is surrounded by a black line." (Thompson(1)). Fruitbodies are 0.05-0.1cm in diameter, "quadrate to hexagonal, black, shining", with a distinct star-shaped, preformed dehiscence mechanism of lighter colored cells, "opening by teeth to expose the dull yellow hymenium". Fruitbodies are "scattered in prominent bleached spots bounded by a black line, intraepidermal, usually accompanied by pycnidia". Pycnidia are 0.1-0.3 mm diameter "appearing before the apothecia mature". (Sherwood).
Microscopic: spores 45-55 x 1-2 microns, colorless, smooth, one end rounded, the other pointed; asci 8-spored, iodine negative; paraphyses quite slender, "gradually widening towards their rounded or irregularly swollen tips", (Thompson), spores 45-65 x 2.0 microns, "narrowly but distinctly sheathed, nonseptate"; asci 8-spored, 70-105 x 8-10 microns, "cylindric-clavate, short-stalked", thin-walled, iodine negative; paraphyses simple, filiform [thread-like], gradually enlarged to 2.0 microns at the apex, "the contents rather granular"; pycnidia 0.1-0.3 mm diameter "appearing before the apothecia mature, intraepidermal, lenticular in cross section", "with a dark brown covering layer"; conidia 4-5 x 1.0 microns, "bacilliform, nonseptate, colorless"; phialides 5-10 x 2-2.5 microns, "in a basal layer, borne on short conidiophores, subulate, without a collarette". (Sherwood)
Habitat / Range
on "dead (rarely living) leaves of a wide variety of angiosperms, notably on Fagaceae and Ericaceae, widespread and common, chiefly in warm temperate areas, summer and fall in the northern part of its range, throughout the year in subtropical areas", (Sherwood)
Similar Species
There are at least nine other Coccomyces species in the Pacific Northwest. 1) Coccomyces arbutifolius was described from BC on Arbutus menziesii leaves (apparently living leaves). The leaves are marked by a faint superficial bloom but there is no bleaching or encircling line, and both ascospores and asci are larger. 2) Coccomyces arctostaphyli, recorded from OR, AB, and Europe, is inconspicuous on leaves of Arctostaphylos uva-ursi (kinnikinnick). 3) Coccomyces castanopsidis, found in OR and CA, is up to 0.4cm across with a bright yellow hymenium, and grows on dead bark and wood of Castanopsis (chinquapin) and Quercus chrysolepis (Canyon Live Oak). 4) Coccomyces heterophyllae occurs on twigs of Tsuga heterophylla (Western Hemlock) in the coastal forests of BC and WA in spring and summer. 5) Coccomyces ledi grows on living twigs of Rhododendron groenlandicum (Labrador-tea) and R. tomentosum (northern Labrador-tea), late summer and early fall, and is common in arctic and alpine localities (including BC, OR, MB, NT, NH, Europe, and Asia). 6) Coccomyces leptideus is common on living and recently killed twigs of Vaccinium myrtillus (bilberry), V. vitis-idaea (lingonberry), Rhododendron macrophyllum (Pacific rhododendron), and Gaultheria shallon (salal). Spores are either 4-spored, with spores 60-90 x 4(5) microns, or 8-spored, with spores 60-90 x 3.0-3.5 microns. It grows in summer and fall, in WA, OR, and Europe. Coccomyces gaultheriae is distinguished from C. leptideus by its shorter, broader ascospores 19-22 x 6-6.5 microns. [C. gaultheriae has been recorded from twigs of Gaultheria shallon from BC by Adolf and Oluna Ceska]. 7) Coccomyces parvulus grows on decorticated wood of various conifers in WA and OR. The colonies look like charred wood and the fruitbodies are only 0.03-0.08cm across and round to elongate, up to twice as long as they are wide. 8) Coccomyces pseudotsugae produces black fruitbodies 0.06-0.12cm across on bark of Pseudotsuga menziesii (Douglas-fir) and Abies grandis (Grand Fir), and has been found in BC, WA, and CA, 9) Coccomyces tumidus produces relatively large, fleshy, rugose, dark brown fruitbodies 0.1-0.2cm across, round to elongated, with a dull yellow to yellowish tan spore-bearing surface. They grow on long dead leaves of a variety of hardwood trees especially oak and beech and other plants including salal and Rubus. The fruitbodies are on bleached areas of the leaf, usually surrounded by a black line. Distribution includes WA, OR, MA, ME, NH, NY, VA, NS, ON, and Europe. 10) Coccomyces coronatus of Europe and eastern North America, with which C. dentatus is frequently confused, "has inflated paraphyses, longer asci and ascospores, less regular apothecia, and rarely occurs on leaves of evergreens". (Sherwood). Kroeger(5) reported C. tumidus from salal in Haida Gwaii, BC.
