Bisporella sulfurina

Description

Bisporella sulfurina is a tiny, lemon-yellow mushroom that grows on decaying wood from deciduous trees. It forms small, bright yellow cups without stalks, which can turn paler as they age, sometimes even white. These cups are very small, reaching up to 1 mm in diameter. You'll often find them clustered together on old stromata of other fungi, like Diatrype, Diatrypella, and Hypoxylon.

This mushroom is unique because it grows in close association with another type of fungus, a pyrenomycete, which has a blackish tissue layer nearby. Bisporella citrina is a similar but larger species that doesn't have this association and typically grows in groups on bark-free hardwoods. Both Bisporella sulfurina and Bisporella citrina produce two-celled ascospores when mature, but the spores of Bisporella citrina are wider. There's also another Bisporella species called B. pallescens, which forms small, whitish cups on hardwoods and also grows on the surface of another fungus called Bispora antennata.

Common names: German (Schwefelgelbes Kernpilz-Becherchen, Schwefelgelbes Kernpilzbecher).

Mushroom Identification

1. Sporocarp

   Apothecia 0.5-2.0 mm broad, sessile, at first urn-like, centrally concave, becoming cushion-shaped to discoid; hymenium glabrous, bright yellow to citrine, slightly translucent; exterior colored like the disc or paler; margin more or less even, lacking hairs; context soft, fleshy, yellowish; odor and taste not investigated.

2. Spores

   8.0-11.0 (13.0) x 2.0-2.5 µm, narrowly ellipsoid to subfusoid, occasionally curved, hyaline, one-septate at maturity, some with droplets; asci eight-spored, uni to biseriate, the tips inamyloid.

3. Habitat

   On hardwoods, gregarious to clustered, fruiting in association with a pyrenomycete; seldom collected because of its size, but probably common.

Look-Alikes

1. Bisporella citrina

   Bisporella citrina is a common mushroom that's larger in size. It doesn't grow with a certain type of fungus. Instead, it often grows in groups on trees without bark. Bisporella citrina has wider spores when it's mature. Another similar mushroom, Bisporella sulfurina, grows on top of another fungus called Bispora antennata. There's also a third type, Bisporella pallescens, which makes small, whitish cups on trees.

Synonyms

1. Calycella sulfurina (Quél.) Boud. 1907

2. Calycina sulfurina (Quél.) Kuntze 1898

3. Helotium sulfurinum Quél. 1880

Photo sources:

Photo 1 - Author: Jerzy Opioła (CC BY-SA 4.0)

Photo 2 - Author: Jerzy Opioła (CC BY-SA 4.0)