13/Sep/2026, 12:13 PM
Kose, Tallinn, Harju, Eesti
Decidious forest edge, near urban road, on Acer platanoides green leaf
59°27'33.8"N 24°50'35.3"E
🌡️ 16°C 🌦️ Sprinkles, scattered clouds 💨 Wind 230° SW->NE, 15 km/h
Original Instagram postRhytisma acerinum
Black Tar Spot
- Scientific identification
- Rhytisma acerinum (Pers.) Fr.
- Family
- Rhytismataceae
- Class
- Leotiomycetes
- Genus
- Rhytisma
Names across languages
- English: Black Tar Spot
- German: Ahorn-Runzelschorf
- Finnish: Vaahterantervatäplä
- Estonian: Vahtra-pigilaik
- Russian: Ритизма кленовая
The scientific profile
From the latest record: 2026-09-13.
Hymenium
Developing inside elongated apothecial ascomata embedded within black stromata
Body
Initially yellow-green leaf spots, developing into slightly raised, glossy tar-black stromata; irregularly circular, often surrounded by a narrow yellow to brownish margin
Hymenium Attachment
Ascomata embedded beneath the surface of the stroma
Stipe
Absent
Description
Spore mass hyaline to whitish
Description
Biotrophic parasite on living maple leaves, especially sycamore and Norway maple; stromata mature on fallen overwintered leaves, releasing ascospores in spring to infect newly emerging foliage
Edibility
Inedible
Fruit body
Fruit body microscopic
Dimensions
Stromata ∅ up to ~15–20 mm
Flesh
Black stromatic tissue embedded within infected leaf tissue
Microscopy
Ascospores very slender, cylindrical to filiform, smooth, hyaline, aseptate, ~60–80 × 1.5–2.5 µm, with a small apical gelatinous appendage; asci cylindrical, 8-spored, ~105–130 × 9–12 µm; paraphyses hyaline, septate, often curved or branched apically; conidia cylindrical, ~6–10 × 1 µm
Overview
Classic black tar spots on maple leaves
1819). K. Svenska Vetensk-Akad. Handl., Ser. 3 40: 104.
Field encounters
Source hashtags
#rhytismaacerinum #mushroomphotos #fungimacro #tarspotfungus #naturephotography
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