Helvella macropus is a species of fungus in the family Helvellaceae of the order Pezizales. Its ascocarps are found in summer and autumn in woodland, usually (though not exclusively) associated with broad-leaved trees.
The fungus was originally described in 1796 by Christiaan Hendrik Persoon, who classified it in the genus Peziza. The type specimen was collected in Sweden. The taxon was transferred to the genus Helvella in 1871 by Petter Adolf Karsten.
The apothecium of Helvella macropus is a stalked, cup-like structure that typically forms a regular, saucer-shaped head measuring 1.5âÂÂ3 cm across. Its spore-bearing surface, or hymenium, varies from yellowish to greyish-brown, and the outer cup (receptacle) is the same colour and densely covered in fine hairs (villose). The supporting stipe is slender and cylindrical, ranging from 2.5 to 12 cm in height and 3âÂÂ5 mm in width, with a pubescent (hairy) surface that emphasises its hollow interior.
Beneath the hymenium lies the medullary excipulum, a loosely interwoven network of brownish hyphae about 4âÂÂ6 üm wide, some inflated to 10âÂÂ20 üm and constricted at their septa. Outside this is the ectal excipulum, where the innermost hyphae also form a textura intricata of cells 10âÂÂ30 üm across. Toward the surface, these cells reorganise into fascicled rows of cylindrical hyphae 20âÂÂ35 üm long by 10âÂÂ15 üm wide, and some extend into tufts of hyphoid hairs up to 200 üm in length. The spore-bearing ascus are pleurorhynchousâÂÂoriginating from a hooked basal cellâÂÂand measure 240âÂÂ300 à13âÂÂ16 üm, each enclosing eight ellipsoid-fusoid ascospores. These spores are 19.5âÂÂ25.8 üm long by 9âÂÂ12.0 üm wide and contain one large plus two to three medium-sized oil droplets (guttules). Interspersed among the asci are sterile paraphysis filaments, 3âÂÂ4 üm wide at the base and swelling to 5âÂÂ9 üm at their club-shaped tips.
Similar species include H. corium, H. cupuliformis, H. fibrosa, H. pezizoides, H. queleti, and Donadinia nigrella.
This species has a wide distribution in the Northern Hemisphere, having been recorded throughout North America, as well as in Central America, Europe, China, and Japan. It can be found on the ground or on rotting wood along with moss.
The species is inedible.