Purple-spored Puffball

Purple-spored Puffball (Calvatia cyathiformis) is one of the larger grassland puffballs, reaching the size of a grapefruit in good conditions. It is broadly pear- or top-shaped, widest above and tapering into a stout, wrinkled, stalk-like sterile base.

Two features define it. First, the mature spore mass is purple to deep purple-brown, a colour no other large Calvatia shows. Second, once the upper wall has broken up and blown away, the sterile base remains rooted in the turf as a thick-walled, vase- or cup-shaped bowl, from which the species takes its epithet cyathiformis, meaning cup-shaped. These persistent bowls are often the most conspicuous sign of the fungus, surviving well into the following season.

It is a familiar fungus of open grassland in North America, particularly the prairies and plains, and of grassy places elsewhere.

Fruiting body

Large, 7–20 cm across, broadly pear-shaped to top-shaped with a rounded head and a stout, tapered, furrowed sterile base. Often occurring in scattered groups or arcs in turf.

Surface

Whitish to pale tan or buff when young, smooth to slightly felted, becoming brownish and characteristically cracking into shallow polygonal patches or scales as the fruit body expands. The skin is thin and papery at maturity.

Interior and spore mass

White and firm inside when young, passing through yellowish and olive shades to a powdery purple, purple-brown or dull violet-brown at maturity. The sterile base is spongy and chambered, and remains paler than the spore mass.

Opening and remains

The upper wall disintegrates irregularly, exposing the spore powder to the wind and eventually leaving the persistent vase-shaped base.

Spore print

Not applicable in the usual sense; the mature spore mass is purple to purple-brown.

It fruits in open grassland — pastures, meadows, lawns, parks, prairies, roadside verges and grazed fields — usually on fairly fertile soil. It sometimes appears in large arcs or fairy rings where the underground mycelium has spread outward for years.

The season is summer to autumn, following heavy rain, with old sterile bases persisting through winter. It is widespread in North America and reported from grassland regions across the Americas, Europe, Africa and Asia.

Calvatia cyathiformis is a grassland saprophyte, decomposing dead roots, thatch and soil organic matter. The extensive perennial mycelium can persist in a single pasture for many years, which is why the fungus tends to fruit in the same places and in expanding rings.

Spore dispersal is entirely by wind: the papery upper wall breaks up and the enormous quantity of purple-brown spores is carried away over days or weeks, leaving the tough basal cup behind.

Calvatia craniiformis is similar in size and shape but its mature spore mass is yellowish to olive-brown, never purple, and its surface is smoother and more wrinkled at the base rather than cracking into polygons. Calvatia gigantea is much larger, nearly spherical, sits on the ground with almost no stalk-like base, and has an olive-brown spore mass. Calvatia utriformis has a coarsely mosaic-cracked surface and an olive-brown spore mass, and favours upland pasture and dunes. Large Lycoperdon species are far smaller and open by a neat apical pore.

Purple-brown spore powder in a large grassland puffball with a persistent vase-shaped base is conclusive.