Collared Earthstar

Description

The collared earthstar is the largest of the earthstars. The young fruiting body looks like a brown bulb partly buried in the ground. As it matures, the outer covering splits into 4–8 fleshy rays that spread out like a star and lift a round, greyish-brown spore sac. The whole fruiting body is usually up to about 11 cm across, rarely more. A distinct collar or "saucer" is usually visible around the sac, which gives the species its name; sometimes, however, it does not form.

It grows in humus-rich, shaded deciduous forests, parks and thickets, often under beeches and oaks, singly or in groups. In Poland it is rare and known from only a dozen or so localities. Old, dried-out fruiting bodies can be persistent and may also be found in winter.

It is distinguished from other earthstars by its large size and the collar beneath the spore sac. Smaller specimens without a collar can be confused with the sessile earthstar or the rosy earthstar. It is inedible, and because of its rarity it is best left where it grows.

Identification features

Cap

A gasteroid species, without a cap. The young fruiting body is an onion-shaped "egg" 1–5 cm in diameter, partly or completely buried in the ground, light brown, darkening with age, sometimes with a pinkish tinge. The exoperidium splits into 4–8 fleshy rays 2–4 cm long and up to 4 mm thick, which spread out like a star and curve downwards, lifting the spore sac. The expanded fruiting body usually reaches about 11 cm in diameter, up to 18 cm according to some descriptions; it is the largest earthstar. The inner (upper) side of the rays is smooth, light or dark brown, sometimes with a reddish tinge, usually cracked into patches to a varying degree. The lower side of the rays is rough and does not become coated with litter or soil. The rays are not hygroscopic.

Hymenophore (underside of the cap)

No gills or tubes. Inside the endoperidium is the gleba: white and firm when young, later brown and powdery. The endoperidium is spherical to slightly flattened, parchment-like, 1–4 cm in diameter, sessile, without an apophysis, greyish brown to ochre-brown. It opens by a pore at the top; the peristome is fibrous, low, slightly raised, with a ragged or torn margin, surrounded by a paler zone. The columella (pseudocolumella) reaches roughly to half the height of the endoperidium.

Stem

No stem; the endoperidium is sessile. Characteristic is the detachment of the fleshy, ochre-grey layer (about 3 mm thick) just at the base of the rays; its edges form a collar or saucer-like base in which the endoperidium rests. The collar may be reduced to a disc or not form at all, especially in a temperate climate.

Flesh

The fleshy layer of the exoperidium is ochre-grey, fairly thick, hard and fibrous when dry. The fruiting body has no distinct smell or taste (no data on smell); the flesh should not be tasted.

Spore print and spores

Spore print (spore mass) brown, powdery. Spores spherical, about 3.5–5.8 µm in diameter (descriptions give different ranges), covered with numerous short, narrow warts up to about 1 µm long. In KOH they fade to pale cinnamon brown, in iodine dark brown.

Habitat and distribution

Ecology. A saprotroph decomposing humus and dead organic matter. Grows on humus-rich soil, in the leaf litter of deciduous forests, around well-rotted stumps, in thickets and parks, mostly in shaded places; often under beeches and oaks. Also observed on wooded coastal dunes and on calcium-enriched soil. Grows singly or, more often, in groups.

Distribution. Cosmopolitan, occurring on all continents except Antarctica. Widespread in Europe, from the Mediterranean zone and the Canary Islands to Sweden and Finland. Rare in Poland, known from a dozen or so localities; on the Red List of plants and fungi of Poland it has category E (endangered). Listed as threatened in several European countries. In Poland it was under strict species protection; since 9 October 2014 it is no longer on the list of protected species.

Fruiting. No clear data on the timing. The fruiting bodies are persistent, and old ones may survive the winter into the following spring or summer; expanded fruiting bodies are usually found from summer to autumn.

What can it be confused with?

• Geastrum fimbriatum (sessile earthstar) — Smaller; it can be confused with small specimens of G. triplex, especially when no collar forms. G. triplex is larger and has a collar beneath the endoperidium.
• Geastrum rufescens (rosy earthstar) — Smaller; it can be confused with small specimens of G. triplex. G. triplex is larger and has a collar beneath the endoperidium.
• Geastrum saccatum (rounded earthstar) — Also smaller; the rays do not always split around the endoperidium, so the lack of a saucer makes identification harder. G. triplex is larger, does not become coated with litter, and has a fibrous peristome surrounded by a paler zone. Protected in Poland (strict protection), not included in the Atlas — do not pick.
• Myriostoma coliforme (salt-shaker earthstar) — Caution: similar protected species (strict protection in Poland), described in the Atlas. Spore sac on several stalks, with many openings; no collar.
• Protected earthstars (Geastrum) — Caution: protected species not included in the Atlas: G. lageniforme, G. berkeleyi, G. elegans, G. schmidelii, G. floriforme, G. campestre, G. hungaricum, G. saccatum and G. fornicatum (strict protection in Poland); G. corollinum and G. quadrifidum (partial protection). They are usually smaller and lack the fleshy collar under the spore sac; reliable identification needs details (mouth of the sac, sac stalk, rays). Do not pick earthstars.

Never rely on a single feature. If you are not sure — do not pick it; show the mushroom to a qualified mushroom expert.

Interesting facts

• The name "triplex" (Latin for "threefold") refers to the three layers of the peridium; the English names are collared earthstar, saucered earthstar and triple earthstar.
• The species was described in 1840 by Franz Junghuhn, who studied the fungi of Indonesia; the type specimen was collected on Java at an elevation of 910–1,520 m above sea level.
• The rays are not hygroscopic, so unlike some other earthstars they do not close and open in response to humidity.
• Spores are released through the opening at the top of the sac, for example when raindrops hit the flexible endoperidium and push the spores out in a puff.