An Enigmatic Star

In Jersey a member of the Geastraceae raises uncertainty over its correct identity
[from the Autumn 2005 issue of The Forayer]

In the new British Checklist, the species Geastrum saccatum Fries, is not recognised and it is not included in British Puffballs, Earthstars and Stinkhorns by Pegler, Lessoe and Spooner, RBG Kew 1995. The current British viewpoint is that European collections are very close to G. triplex or G. lageniforme. There are also some distinct similarities with G. fimbriatum in that the fruitbodies are non-hygroscopic, often of similar size and with papery thin saccate exoperidia. Kew mycologist Peter Roberts advises that old British collections called ‘G. saccatum' are mostly filed under G. lageniforme.

Not all European mycologists agree with this argument. G. saccatum is included in Nordic Macromycetes but G. lageniforme is not and since specimens answering to Fries' description have turned up recently in the Channel Islands, collected by the Jersey Fungus Recording Group, the issue is worth a closer look.

The historical facts are not in dispute. In 1829 Fries described a specimen collected in Brazil by Hornemann, of which no material has survived. Fries also conceded that Hornemann's collection 'is very different from the European ones'. But Fries' observations on this score, or rather lack of them, also suggests that back in 1829 he was not fully acquainted with European species of Geastrum. He omits, for example, to discuss important features including the shape of the unexpanded fruit body and the presence and shape of the columella. In other words his 'very different' may not hold too much significance.

In his substantial monograph on the Geastraceae published as part of the Fungiflora, Oslo (1989), Stellan Sunhede argues for retention of a distinct species named G. saccatum. This produces a mostly small to medium-sized mature fruitbody with a non-hygroscopic exoperidium that is more or less saccate when expanded, with 5-8 rays. The endoperidial body is sessile and the peristome is normally fibrillose and fairly well delimited.

Comparing European collections of what Sunhede believes we should respect as G. saccatum against those of other similar species, he points out that G. saccatum is generally a smaller species than G. fimbriatum , the endoperidial body measuring in at 5-20mm across, whilst G. fimbriatum is nearer 9-25mm. The peristome in G. saccatum is fairly well delimited but in G. fimbriatum its border is indistinct. The mycelial layer (the outermost layer of the exoperidium) of G. fimbriatum is covered with encrusting debris whilst that of G. saccatum is not. Spores of G. saccatum are larger, 4.5-6 microns against 3-4 microns.

Compared with the morphology of G. triplex, there is a similarly shaped fruitbody in G. saccatum and both have non-encrusted mycelial layers, but the fruitbody of G. saccatum is generally much smaller and only rarely possesses a pseudoparenchymatous collar or cup while G. triplex normally has one.

The mycelial layer of G. triplex, often with longitudinal cracks on the rays is of thin-walled clamped hyphae. That of G. saccatum rarely cracks and is built up from an outer layer of thick-walled, unclamped hyphae and an inner layer of thin-walled hyphae with clamps.

Sunhede agrees that G. saccatum and G. lageniforme possess marked similarities, but also points to clear differences in the mycelial layers of the two species and in the shape of the basidia.

Pegler, Lessoe and Spooner describe the mycelial layer of G. lageniforme as being dull yellowish brown or pale brown, often with paler longitudinal splits and non-encrusted. Sunhede notes that in G. saccatum it is comparatively thick, also non-encrusted, more or less even or slightly wrinkled, with or without longitudinal cracks in the rays, consisting of an outer, prominent, felty ochraceous to brownish layer and an inner thin to rather thick, loose to more or less mealy, beige to whitish layer that may remain intact even in over wintered specimens.

Pegler, Lessoe and Spooner note that in G. lageniforme basidia were 'not seen'. Sunhede describes the basidia of G. saccatum as possessing a basal clamp connection, when young being bladder-like to clavate and in age having an apical bulge or gradually narrowing towards a blunt tip.