Spongiforma is a genus of sponge-like fungi in the family Boletaceae. Newly described in 2009, the genus contains two species: S. thailandica and S. squarepantsii. The type species S. thailandica is known only from Khao Yai National Park in central Thailand, where it grows in soil in old-growth forests dominated by dipterocarp trees. The rubbery fruit bodies, which has a strong odour of coal-tar similar to Tricholoma sulphureum, consists of numerous internal cavities lined with spore-producing tissue. S. squarepantsii, described as new to science in 2011, is found in Malaysia. It produces sponge-like, rubbery orange fruit bodies with a fruity or musky odour. These fruit bodies will—like a sponge—resume their original shape if water is squeezed out. The origin of the specific name derives from its perceived resemblance to the cartoon character SpongeBob SquarePants. Apart from differences in distribution, S. squarepantsii differs from S. thailandica in its colour, odour, and spore structure.
The fruit bodies of Spongiforma species have a brain-like to sponge-like form, and grow on the surface of the ground. They do not have a stalk, and lack a layer of outer skin. The small cavities (locules) of the fruit body are irregular in outline and measure between 2 and 20 mm (0.08 and 0.8 in) in diameter. They are lined with a smooth, greyish-orange to brown or reddish brown hymenium (spore-bearing tissue), with sterile ridges that range in colour from white to cream. The columella (a column-like structure extending up into the fruit body) is poorly developed, pear-shaped, cream-coloured, and attached at the base to white rhizomorphs. The basidiospores are brown to vinaceous-brown in mass, almond-shaped, bilaterally symmetrical, and finely wrinkled. Spores bear a central apiculus (a region that was once attached to the sterigmata at the end of a basidium) and a small apical pore. The spores are reddish-brown in water, violet grey in 3% potassium hydroxide, inamyloid, and cyanophilic (turning red in the stain acetocarmine). The basidia are four-spored, and do not discharge the spores forcibly. Cystidia are common on the sterile locule edges; they are hyaline (translucent) and range in shape from cylindrical to ventricose (swollen in the middle) or rostrate (with a beaklike proboscis). The hyphae of the flesh are gelatinous and inamyloid. Clamp connections are absent from the hyphae.[1]
The type species S. thailandica was first described scientifically in 2009 by Egon Horak, Timothy Flegel and Dennis E. Desjardin, based on specimens collected in July 2002 in Khao Yai National Park, central Thailand, and roughly three years later in the same location. Before this, S. thailandica had been reported and illustrated in a 2001 Thai publication as an unidentified species of Hymenogaster.[1][2]
S. squarepantsii was first described scientifically in 2011 in the journal Mycologia, authored by a team headed by Desjardin with Kabir Peay, and Thomas Bruns. The description was based on two specimens collected by Bruns in 2010 in Lambir Hills National Park, in Sarawak, Malaysia. The species was first mentioned in the scientific literature in 2010 in a study of the ectomycorrhizal mushrooms in a tropical dipterocarp rainforest in Lambir Hills, although it was not formally described in this publication.[3]
The genus name Spongiforma refers to the sponge-like nature of the fruit body. The specific epithet thailandica denotes the country in which the type species is found;[1] the epithet squarepantsii honors the well-known cartoon character SpongeBob SquarePants.[4] The unusual epithet garnered the species attention in the popular press.[5][6][7]