Yellow Fairy Cups

Appearance

Fruit bodies begin as spherical, closed globules, before expanding. The smooth, bright yellow fruit bodies are small—typically less than 3 mm in diameter and up to 1 mm high—and shallowly cup- or disc-shaped. The inner surface is smooth, and bright yellow, while the outer surface is a paler yellow. In mass, the spore color is white. The stalk is broad, pale yellow in color, and short to nearly absent; when present it is rarely more than 1 mm. The fruit bodies may be so numerous that their shapes are distorted by overcrowding. Fruit bodies that have dried are wrinkled and have a dull orangish-brown color. The fruit bodies have no distinctive taste nor odor, and are not edible.

The smooth spores are roughly elliptical, measuring 8–14 by 3–5 μm; in maturity they have one cross-wall, and oil drops at either end. The asci measure 100–135 by 7–10 μm. The paraphyses are shaped liked narrow cylinders with diameters up to 1.5 μm, and have tips that are rounded or somewhat club-shaped. β-Carotene is the predominant pigment responsible for the yellow color of the fruit body.

Naming

There are several small yellow discomycetes with which "Bisporella citrina" might be confused. Lookalikes include the acorn cup that grows on fallen acorns and hickory nuts. The green stain fungus forms blue-green cups, and stains its wood substrate bluish-green. "Lachnellula arida" is up to 6 mm in diameter, and has hairs around the edge of its cup, and its outer surface is covered with short brown hairs.
Fruit bodies of "Bisporella sulfurina" have a coloration similar to "B. citrina", but they are smaller and grow in clusters on old, blackened, fungal stroma on wood.

Other lookalikes include "Hymenoscyphus" species, including "H. calyculus", but these can be distinguished by their distinct stalks, and growth on smaller woody debris like sticks and twigs, rather than logs and stumps. Many other small, yellow discos have fringed or hairy margins to the discs, like "Anthracobia melaloma"; this latter species grows on or near moss, rather than wood. "Chlorosplenium chlora" is another small cup fungus resembling "B. citrina". It has a bright yellow outer surface, but the hymenium becomes develops greenish tints in age. The common jellyspot fungus is usually smaller but can approach the dimensions of "B. citrina". Similar in color, its fruit bodies are usually blob-like rather than cup shaped. Another cup fungus that grows on dead beech wood is "Neobulgaria pura", but its fruit bodies are larger, ranging from 2–4 cm.

Also similar are "Bisporella pallescens", "Dacrymyces capitatus", "Guepiniopsis alpina", and members of "Octospora".

Distribution

"Bisporella citrina" is saprobic, and so obtains nutrients by breaking down complex organic molecules into simpler ones. Fruit bodies are typically encountered growing in dense clusters on the surface of rotten wood, particularly beech. They have also been found growing on the fruit bodies of the polypore fungus "Daedaleopsis confragosa". In a study of the succession of fungi associated with the decay of a 120-year-old healthy beech tree uprooted by strong winds, "B. citrina" was found on the wood about three years after the fall. It appeared after early colonizers such as "Quaternaria quaternata", "Tubercularia vulgaris", and "Bulgaria inquinans", and was followed by "Stereum hirsutum" and "Nectria cinnabarina".

The widespread fungus is known from North Africa, Asia, Europe, North America, Central and South America, Australia, and New Zealand. It is one of the most common of the small discomycetes.

Habitat

"Bisporella citrina" is saprobic, and so obtains nutrients by breaking down complex organic molecules into simpler ones. Fruit bodies are typically encountered growing in dense clusters on the surface of rotten wood, particularly beech. They have also been found growing on the fruit bodies of the polypore fungus "Daedaleopsis confragosa". In a study of the succession of fungi associated with the decay of a 120-year-old healthy beech tree uprooted by strong winds, "B. citrina" was found on the wood about three years after the fall. It appeared after early colonizers such as "Quaternaria quaternata", "Tubercularia vulgaris", and "Bulgaria inquinans", and was followed by "Stereum hirsutum" and "Nectria cinnabarina".

The widespread fungus is known from North Africa, Asia, Europe, North America, Central and South America, Australia, and New Zealand. It is one of the most common of the small discomycetes.