What You Should Know
Bisporella citrina is a species of fungus in the family Helotiaceae. The fungus produces tiny yellow cups, often without stalks, that fruit in groups or dense clusters on decaying deciduous wood that has lost its bark. The widely distributed species is found in North Africa, Asia, Europe, North America, and Central and South America. Found in late summer and autumn, the fungus is fairly common, but is easily overlooked owing to its small size. It can be distinguished from other look-alikes by its elliptical spores, which have a central partition, and an oil drop at each end.
This species is saprobic, and so obtains nutrients by breaking down complex organic molecules into simpler ones. It is generally regarded as inedible.
Other names: Lemon Disco, Yellow Fairy Cups, Geel schijfzwammetje (Netherlands), Voskovička citrónová (Czech Republic), Zitronengelbes Holzbecherchen (German).
Bisporella citrina Mushroom Identification
Cup-shaped to disc-shaped; up to 3 mm across; smooth above and below; with a tiny tapering stem or nearly without a stem; smooth; uniformly bright yellow.
Saprobic on decaying logs and stumps of hardwoods and conifers; growing in dense clusters; widely distributed in North America.
September to November.
Spores 9-14 x 3-5 µ; elliptical; with an oil droplet at each end; smooth; often septate by maturity. Asci 100-135 x 7-10 µ. Paraphyses narrowly cylindric, with rounded or slightly clavate apices.
Bisporella citrina Look-Alikes
Usually smaller and similar in color.
Similar, but has a well-developed stem and fruits on sticks and twigs, rather than logs or stumps.
Grows on fallen acorns and hickory nuts.
The green stain fungus forms blue-green cups and stains its wood substrate bluish-green.
Up to 6 mm (0.24 in) in diameter, and has hairs around the edge of its cup, and its outer surface is covered with short brown hairs.
Fruit bodies have a coloration similar to B. citrina, but they are smaller and grow in clusters on old, blackened, fungal stroma on wood.
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 grows on dead beech wood, but its fruit bodies are larger, ranging from 2–4 cm (0.8–1.6 in).
Macroscopically is very similar. It grows on willows. Microscopically, they differ in paraphyses without granular content and longer spores.
Has smaller, undivided spores without drops. It grows on beech and hazel.
Bisporella citrina Taxonomy and Etymology
In 1789 German naturalist August Batsch described this species as Peziza citrina. Jean Louis Émile Boudier transferred the species to Calycella in 1885. Another historical name for the fungus was derived from Johann Hedwig's 1789 Octospora citrina. Fries referred Hedwig's name to Helotium in 1846, and for several decades the fungus was known as either Calycella citrina or Helotium citrinum, depending on which generic concept the author accepted.
In a 1974 publication, Richard Korf noted that the generic name Helotium competes with a basidiomycete genus of the same name, and under the rules of botanical nomenclature. He also pointed out that the generic name Calycella could not be used, as it is a synonym of an older name Calycina, which contains species that bear no taxonomic relationship to Helotium citrinum. Accordingly, he formally transferred Helotium citrinum to Bisporella, to produce the new combination Bisporella citrina. Korf further noted that since Bisporella was published by Pier Andrea Saccardo in 1884, it had priority over Boudier's 1885 Calycella. Calycella has since been folded into Bisporella.
The specific epithet citrina is derived from the Latin citrin, meaning "lemon yellow".
Bisporella citrina Synonyms and Varieties
Calycella citrina (Hedw.) Boud., 1907
Bisporella citrina (Batsch) Korf & S.E. Carp. 1974
Bisporella claroflava (Grev.) Lizon & Korf 1995
Calycella citrina (Hedw.) Boud. 1885
Calycella claroflava (Grev.) Boud. 1907
Calycella flava (Klotzsch ex W. Phillips) Boud. 1907
Calycina citrina (Hedw.) Gray 1821
Calycina clariflava (Grev.) Kuntze 1898
Calycina flava (Klotzsch) Kuntze 1898
Helotium citrinum (Hedw.) Fr. 1849
Helotium flavum Klotzsch 1887
Octospora citrina Hedw. 1789
Peziza citrina (Hedw.) Pers. 1794
Peziza citrina Batsch 1789
Peziza claroflava Grev. 1824
Calycella citrina var. citrina (Hedw.) Boud.
Helotium citrinum subsp. citrinum (Hedw.) Fr.
Helotium citrinum subsp. turfaceum P. Karst.
Helotium citrinum var. citrinum (Hedw.) Fr.
Helotium citrinum var. pallidum Cooke, 1879
Peziza citrina f. citrina Batsch
Peziza citrina f. filicina Fr.
Peziza citrina forma citrina Batsch 1789
Peziza citrina subsp. citrina Batsch
Peziza citrina subsp. citrina Batsch 1789
Peziza citrina var. albescens Pers.
Peziza citrina var. albescens Pers., 1822
Peziza citrina var. albicans Pers.
Peziza citrina var. albicans Pers., 1822
Peziza citrina var. albida Alb. & Schwein.
Peziza citrina var. albida Alb. & Schwein., 1805
Peziza citrina var. citrina Batsch
Peziza citrina var. lenticularis Pers.
Peziza citrina var. lenticularis Pers., 1822
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