What You Should Know
Helvella acetabulum is a species of fungus in the family Helvellaceae, order Pezizales. This relatively large cup-shaped fungus is characterized by a mid-brown fruit body with prominent pallid to cream-colored branching ribs resembling a cabbage leaf; for this reason, it is sometimes known as the Cabbage-leaf Helvella. There are other similar species so it is best to have a specimen checked by an expert.
In most areas of North America, Helvella acetabulum is late spring and early summer species - but in the Rocky Mountains it is sometimes found in late summer, and it can appear overwinter in warm climates.
Other names: Ribbed-stalked Cup, Vinegar Cup, Brown-ribbed Elfin-cup.
Helvella acetabulum Mushroom Identification
Probably mycorrhizal; growing alone or gregariously, under hardwoods or conifers, often in the vicinity of stumps or decaying wood; spring and early summer - or late summer in the Rocky Mountains, or winter and spring in coastal California; widely distributed in North America.
2-12 cm across; cup-shaped, sometimes becoming more or less flat in age; upper surface yellow-brown to brown, bald, and smooth; undersurface brown to yellow-brown, sometimes paler near the stem, finely fuzzy near the margin, with forked whitish to brownish ribs that extend from the stem, sometimes almost to the margin.
Thin; brittle; brownish; whitish and chambered in the stem.
2-9 cm long; up to 5 cm thick; becoming broader near the cap; deeply pocketed and ribbed with sharp-edged (occasionally blunt) forking ribs that extend onto the undersurface of the cap; whitish to brownish; finely hairy.
KOH negative on all surfaces and flesh.
Spores 16-20 x 11-14 µ; elliptical; smooth; with one central oil droplet. Asci 8-spored. Paraphyses cylindric with clavate or merely rounded apices; 4-6 µ wide; hyaline to brownish.
Helvella acetabulum Look-Alikes
Has a darker cup, a short stipe of rounded folds rather than ribs.
Has a well-developed ribbed stipe, but the ribs seldom extending past the base of the cup.
Has ribs that extend halfway up the sides of the fruit body, but the color of the cup is pale to dark gray rather than cream.
The fruit bodies also resemble those of H. costifera, but the latter species is distinguished by its grayish to grayish-brown hymenium; like H. acetabulum, it has ribs that extend to most of the outside of the fruit body. There are sometimes intermediate forms between the two species, making them difficult to distinguish.
Is also similar to H. acetabulum, but has a lighter-colored hymenium, a robust stem, and the margin of the fruit body is often bent over the stem at maturity. In contrast, H. acetabulum never has the edge of the fruit body bent over the stem, and the stem is "indistinct or prominent, but never robust".
Helvella acetabulum Taxonomy
The fungus was first named Peziza acetabulum by Carl Linnaeus in his 1753 Species Plantarum. It was given its current name by French mycologist Lucien Quélet in 1874 after having been placed in various Peziza segregates: Joachim Christian Timm placed it in Octospora (1788), Samuel Frederick Gray in Macroscyphus (1821), and Leopold Fuckel in Acetabula (1870). The trend wouldn't end there. Claude Casimir Gillet placed it in Aleuria in 1879, and Otto Kuntze in his new Paxina (of which it would later be designated type species) in 1891.
Described independently as Peziza sulcata by Persoon in 1801, it was placed under that name in both Paxina and Acetabula—alongside its precursor as both taxa were still considered separate at the time. Finally, Frederic Clements renamed Acetabula as Phleboscyphus in 1903 and improperly reused Fuckel's name as the basionym of his Phleboscyphus vulgaris.
The specific epithet acetabulum means "little vinegar cup", and was the Latin word for a small vessel used for storing vinegar.
Photo 1 - Author: Sava Krstic (sava) (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 2 - Author: Ron Pastorino (Ronpast) (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 3 - Author: Gerhard Koller (Gerhard) (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 4 - Author: Ron Pastorino (Ronpast) (Creative Commons Attribution-Share Alike 3.0 Unported)