Tuesday, 8 January 2013

Slime mould lurks in shadow of giant inflorescence

   by Tom May (Royal Botanic Gardens Melbourne / Fungimap)  

Cribraria intricata on wood chip mulch in Titan Arum pot, Royal Botanic Gardens Melbourne, December 2012
[Photo: Katie O’Brien]

The world’s largest inflorescence (flower cluster) unfurled on Christmas Day at Royal Botanic Gardens Melbourne. The inflorescence of the Corpse Flower or Titan Arum Amorphophallus titanum towers more than 2 metres. In a delightful contrast, wood chip mulch in the Titan Arum flower pot was dusted with tiny golden globes. At first, Garden’s horticulturalists were concerned about a possible pathogenic fungus; but the globes turned out to be fruit-bodies of the slime mould Cribraria intricata.

Slime moulds have an amoeba-like slimy stage (the plasmodium) which at maturity transforms into many individual fruit-bodies which produce powdery spores. The plasmodial stage feeds on bacteria and other microscopic life, and so the appearance of slime moulds in plant pots is nothing to be concerned about, but rather part of natural food webs.

Fungimapper Paul George provided the identification as Cribraria intricata, noting that ‘spores measure about 6 micrometres in diameter’.
Cribraria intricata fruit-bodies [Photo: Val Stajsic].

Fruit-bodies of Cribraria intricata are composed of a minute globe (0.5-0.7 mm diameter), nodding on a thin stem. Spores are produced within the globe, initially held in place by a spore-sac with a solid cup-like section at the base and an outer framework like finely spun wire. The wiry network has slight thickenings at the joins, as depicted in the beautiful celebrations of nature’s artistry in Ernst Haeckel’s Kunstformen der Natur (Art Forms of Nature)  - with the spore-sac in an upright position.

Despite their tiny size, slime moulds have been known to science for several centuries and Cribraria intricata was first described by the German botanist Heinrich Schrader in 1797.