Diderma subasteroides

Diderma subasteroides is a myxomycete in which the fruit body (up to about 1.75 millimetres tall) consists of a spore capsule atop a stem. The capsule is between 0.5 and 1 millimetre in diameter, hemispherical (or a little flattened and more discoid) and shiny brown. The stem is pale brown, wrinkled, about 2/3 the total fruit body height, flared at the base and arises from a circular, pale brown hypothallus (this looks like a thin layer of varnish on the substrate).  

The capsule splits radially along several dehiscence lines that reach the apex and the segments then fold out to create a star-like shape. Once open the dark purplish-brown, powdery spores are exposed to view. The spores are held within a capillitium (a network of microscopically thin threads) and a columella is present. In many columella-possessing myxomycetes the columella is a pronounced elongation of the stem through the middle of the spore capsule but in Diderma subasteroides the columella is greatly reduced and is visible as a somewhat cushion-like pad at the centre of the open star.        

The open star is white because there is a layer of lime granules on the inner side of the brown outer wall (and the capsule wall is in fact three-layered, there being an inconspicuous membrane on the inner side of the lime layer).      

This species was first described from Argentina in 1971 and since then has been reported from a number of countries, but still seems to be an uncommon species. It is found on rotting wood or ground litter. 

Look-alikes

As the name implies, Diderma subasteroides is very similar to Diderma asteroides and the macroscopic difference between the two is that the latter is either stemless or with a very short stem at most. Several other dark-spored, star-like myxomycetes are known (though not all have been reported from Australia) and while each of these may match Diderma subasteroides on one or two points, none has the same combination of stalk length, capsule shape, capsule colour, limy layer and columella noted above,