honeycomb coral slime mold

Protostelid slime molds are relatively unknown and easily overlooked. They were first recognized in the early 1960s and have been little studied since. There are 36 currently accepted species, and possibly twice that number of undescribed species. Most are microscopic. Only a few are visible to the naked eye.

Honeycomb coral slime mold, also called simply coral slime, is the most commonly encountered protostelid slime mold and may be the most common slime mold of any kind in the world. It occurs on every continent except Greenland and Antarctica. In the United States it is common east of the Great Plains, including Minnesota, and west of the Rocky Mountains. It is absent in the arid west. It is found on shaded rotting wood of fallen logs and branches, in open, wet to moderately moist deciduous, coniferous, and mixed forests. It does not feed on the wood but on bacteria associated with the rotting wood. It can form extensive colonies one meter or more long. It is very short lived, appearing after a soaking rain and disintegrating in just a few days.

Honeycomb coral slime mold first appears as a thin, watery, translucent, mucus-like layer of protoplasm (plasmodium). It creeps across the substrate, engulfing bacteria, protozoa, and particles of nonliving organic matter. Eventually, the plasmodium fruits, converting to spore-bearing structures (sporocarps). The conversion takes about six hours.

The sporocarps are erect, slender, translucent columns appearing usually in clusters of three or more. The clusters often form patches 4″ or more in diameter. The columns are 1 ⁄32″ to ⅜″ (1 to 10 mm) long, 1 ⁄64″ to 3 ⁄64″ (0.5 to 1.0 mm) in diameter, and tapered. They may be branched or unbranched. When they first appear they are slimy, translucent, and usually white, rarely pink or yellow. Later, they have a frosted or powdery appearance due to a dense covering of tiny, white, spores on long, thread-like stalks. The spores may actually be one-celled sporangia.

It is not edible.

No similar species in Minnesota

Open, wet to moderately moist, deciduous, coniferous, and mixed forests

June through October

Sources

24, 26, 29, 30, 77.

Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu, 6/23/2025).

Common and widespread

Higher ranking
There is ongoing disagreement about the classification of slime molds above the rank of genus. The ranking above follows iNaturalist. It is not in agreement with Index Fungorum, MycoBank, MycoPortal, ITIS, Global Biodiversity Information Facility (GBIF), or Catalogue of Life, none of which agree with iNaturalist or with each other.

Ceratiomyxa
Jules Cimon

Ceratiomyxa
alopez2006

Ceratiomyxa fruticulosa sporangia development
Daniel Brunner

Ceratiomyxa fruticulosa (O.F. Müll.) T. Macbr. 1899
The wonderful world of mycology

Ceratiomyxa fruticulosa, the coral slime mold
Cyanescentinel

Location: Magelssen Bluff Park

Location: Woodbury, Minnesota