Spongiforma squarepantsii

Did You Know?

• The species was first collected in Lambir Hills National Park, Sarawak, Malaysia, which receives about 3500 mm of rain yearly with average temperatures from 24 to 32 °C.
• The fruit body structure allows it to quickly revive when dry by absorbing moisture from the air.
• The distinctive odour may indicate that spore dispersal is mediated by animals.

Taxonomy and classification

The species was first described online in May 2011 in the journal Mycologia by American mycologists Dennis E. Desjardin, Kabir Peay, and Thomas Bruns, based on two specimens collected by Bruns in 2010 in Lambir Hills National Park, Sarawak, Malaysia. It had appeared in a 2010 study of ectomycorrhizal mushrooms in a tropical dipterocarp rainforest in Lambir Hills but was not formally described then. Initially uncertain whether the new species belonged to Basidiomycota or Ascomycota due to its unusual form, the authors later determined it aligned with Spongiforma, a genus newly described from dipterocarp forests of Thailand in 2009.

Molecular analysis showed a 98% match between ribosomal DNA sequences of the Bornean species and Spongiforma thailandica. The genus name Spongiforma refers to the sponge-like fruit body, while the specific epithet squarepantsii is a Latinisation of the Nickelodeon cartoon character SpongeBob SquarePants, whose shape was said to resemble the fungus. The editors of Mycologia initially rejected the epithet as frivolous, but the authors insisted they could name it whatever they liked.

Description

Spongiforma squarepantsii produces a bright orange, roughly round or oval fruit body that is 3 to 5 cm wide and 2 to 3 cm tall. It has no stem, but does contain a small cord of sterile tissue, called a columella, that reaches into the center. The outer surface is deeply ridged and folded, giving it a brain-like look, and feels spongy and rubbery; if squeezed to remove water, it bounces back to its original shape. The surface is covered with irregular, large cavities (locules) that range from 2 to 10 mm across, lined with spore-making tissue.

The ridges around these cavities are pale orange or lighter and have tiny hair-like projections. The mushroom smells strongly, described as either vaguely fruity or intensely musty. Its tissue turns purple when a drop of 3% potassium hydroxide (KOH) is applied. The spore mass is reddish-brown or deep mahogany.

Individual spores are almond-shaped, 10 to 12.5 micrometers long by 6 to 7 micrometers wide, with thick walls 0.5 to 1.2 micrometers thick. They have a small central apiculus and a coarsely warty surface that looks rusty brown in water. In 3% KOH, spores become pale lilac grey, and the warts swell into pustules that loosen and dissolve. Spores turn reddish-brown with Melzer's reagent (dextrinoid) and red in acetocarmine (cyanophilic).

The basidia are club-shaped and four-spored, with sterigmata up to 9.5 micrometers long. The locule ridges consist of erect cystidia mixed with chains of erect cylindrical hyphae 4 to 6 micrometers wide; cystidia are roughly cylindrical, 20 to 60 micrometers long by 4 to 9 micrometers wide. No clamp connections are found in the hyphae. The related Spongiforma thailandica has larger fruit bodies (5 to 10 cm wide, 4 to 7 cm tall), a gleba that starts pale greyish-orange to brownish-grey, smells like coal tar, and has spores with less prominent warts.