Astraeus hygrometricus

Description

Astraeus hygrometricus is a species of fungus in the family Diplocystaceae. Young specimens resemble a puffball when unopened. In maturity, its resamples earthstar shape that is a result of the outer layer of fruit body tissue splitting open in a star-like manner. The rays have an irregularly cracked surface, while the spore case is pale brown and smooth with an irregular slit or tear at the top. The gleba is white initially but turns brown and powdery when the spores mature. It is ectomycorrhizal species that grows in association with various trees, especially in sandy soils. A. hygrometricus was previously thought to have a cosmopolitan distribution, though it is now thought to be restricted to Southern Europe, and Astraeus are common in temperate and tropical regions.

Despite a similar overall appearance, A. hygrometricus is not related to the true earthstars of genus Geastrum, although historically, they have been taxonomically confused.

The tough, leathery fruiting bodies of A. hygrometricus can persist for months but are easily overlooked, especially in dry weather, when the rays fold tightly over the spore sac.

It is edible in Northern Thailand. In North American sources list A. hygrometricus as inedible, in some cases because of its toughness. However, they are regularly consumed in Nepal and South Bengal, where "local people consume them as delicious food". They are collected from the wild and sold in the markets of India.

Common names: Hygroscopic Earthstar, The False Earthstar, Barometer Earthstar, Water measurer, Estrella de Tierra (Spain), Weerhuisje (Netherlands), Wetterstern (German), Hvězdák Vlhkoměrný (Czech Republic).

Mushroom Identification

1. Fruiting Body

   2 – 8 cm in diameter. A more or less spherical spore case sitting atop pointed rays that fold over the spore case in dry conditions.

2. Spore Case

   1 – 1.5 cm across; more or less spherical; dry; matted-fibrillose; papery; rupturing at the top with maturity; whitish becoming brownish.

3. Interior

   White and fleshy when young; becoming chocolate brown and powdery.

4. Rays

   Numbering 6 – 10; more or less triangular; about 1 mm thick; inner/upper surface dark brown to black, becoming finely cracked overall; outer/lower surface brown, matted-fibrillose, usually covered with sand.

5. Habitat

   Saprobic; growing alone, scattered, or gregariously in sandy soil, especially in disturbed-ground areas; summer and fall (overwinter in warmer climates). It has been collected in Africa, Asia, Australia, Europe, North America, and South America.

6. Spore Print

   Brown.

7. Microscopic Features

   Spores 7.5–10 µm; globose; echinate; spines densely crowded, about 1 µm long; brownish golden in KOH. Capillitial threads 2.5–7 µm; wide; yellowish to brownish in KOH; roughened; thick-walled.

Look-Alikes

1. Astraeus pteridis

   A related species is less common but considerably larger, between 12 and 15 cm broad. It is found mostly north of the San Francisco Bay Area.

2. Astraeus odoratus

   Distinguished from A. hygrometricus by a smooth outer mycelial layer with few adhering soil particles, 3–9 broad rays, and a fresh odor similar to moist soil. The spore ornamentation of A. odoratus is also distinct from A. hygrometricus, with longer and narrower spines that often joined.

3. Astraeus asiaticus

   Has an outer peridial surface covered with small granules, and a gleba that is purplish-chestnut, compared to the smooth peridial surface and brownish gleba of A. hygrometricus. The upper limit of the spore size of A. asiaticus is larger than that of its more common relative, ranging from 8.75 to 15.2 μm.

4. Astraeus koreanus

   Differs in its smaller size, paler fruit body, and a greater number of rays; microscopically, it has smaller spores (between 6.8 and 9 μm in diameter), and the spines on the spores differ in length and morphology. It is known in Korea and Japan.

Uses

This earthstar has been used in traditional Chinese medicine as a hemostatic agent; the spore dust is applied externally to stop wound bleeding and reduce chilblains. Two Indian forest tribes, the Baiga and the Bharia of Madhya Pradesh, have been reported to use the fruit bodies medicinally. The spore mass is blended with mustard seed oil, and used as a salve against burns.

Astraeus hygrometricus Bioactive Compounds

Extracts from A. hygrometricus containing the polysaccharide named AE2 were found to inhibit the growth of several tumor cell lines in laboratory tests, and stimulated the growth of splenocytes, thymocytes, and bone marrow cells from mice. The extract also stimulated mouse cells associated with the immune system; specifically, it enhanced the activity of mouse natural killer cells, stimulated macrophages to produce nitric oxide, and enhanced the production of cytokines. The activation of macrophages by AE2 might be mediated by a mitogen-activated protein kinase pathway of signal transduction. AE2 is made of the simple sugars mannose, glucose, and fucose in a 1:2:1 ratio.

In addition to the previously known steroid compounds ergosta-7,22-diene-3-ol acetate and ergosta-4,6,8-(14),22-tetraene-3-one, three unique triterpenes—derivatives of 3-hydroxy-lanostane—have been isolated from fruit bodies of A. hygrometricus. The compounds, named astrahygrol, 3-epi-astrahygrol, and astrahygrone (3-oxo-25S-lanost-8-eno-26,22-lactone), have δ-lactone (a six-membered ring) in the side chain—a chemical feature previously unknown in the basidiomycetes. A previously unknown steryl ester (3β, 5α-dihydroxy-(22E, 24R)-ergosta-7,22-dien-6α-yl palmitate) has been isolated from mycelia grown in liquid culture. The compound has a polyhydroxylated ergostane-type nucleus.

Ethanol extracts of the fruit body are high in antioxidant activity, and have been shown in laboratory tests to have anti-inflammatory activity comparable to the drug diclofenac. Studies with mouse models have also demonstrated hepatoprotective (liver-protecting) ability, possibly by restoring diminished levels of the antioxidant enzymes superoxide dismutase and catalase caused by experimental exposure to the liver-damaging chemical carbon tetrachloride.

History

In 1801 Christian Hendrik Persoon placed this mushroom in the genus Geastrum. According to the American botanist Andrew P. Morgan, however, the species differed from those of Geastrum in not having open chambers in the young gleba, having larger and branched capillitium threads, not having a true hymenium, and having larger spores. Thus, in 1889, Morgan established Geaster hygrometricum of Persoon as the type species of his new genus Astraeus.

The specific name is derived from the Greek words ὑγρός (hygros) 'wet' and μέτρον (metron) 'measure'.

Synonyms and Varieties

• Geastrum hygrometricum Pers., 1801

• Astraeus stellatus (Scop.) E. Fisch. 1900

• Geaster fibrillosus Schwein., 1822

• Geastrum decaryi Pat.

• Geastrum fibrillosum Schwein. 1822

• Geastrum hygrometricum Pers. 1801

• Geastrum stellatum (Scop.) Wettst. 1885

• Geastrum vulgaris Corda, 1842

• Lycoperdon stellatus Scop. 1772

• Astraeus hygrometricus f. decaryi (Pat.) Pat. 1928

• Astraeus hygrometricus f. ferrugineus V.J. Staněk 1958

• Astraeus hygrometricus var. hygrometricus (Pers.) Morgan 1889

• Geastrum hygrometricum ß anglicum Pers. 1801

• Geastrum hygrometricum var. hygrometricum Pers., 1801

• Geastrum hygrometricum var. paucilobatum Wettst., 1885

Photo sources:

Photo 1 - Author: bjoerns (CC BY-SA 4.0)

Photo 2 - Author: Richard Sullivan (enchplant) (CC BY-SA 3.0)

Photo 3 - Author: bjoerns (CC BY-SA 4.0)

Photo 4 - Author: bjoerns (CC BY-SA 4.0)

Photo 5 - Author: GLJIVARSKO DRUSTVO NIS from Serbia (CC BY-SA 2.0)