Summary: Features include 1) fruiting on hardwood that starts as colorless or white pustules, becoming brain-like or occasionally somewhat leaf-like, spreading out to 10cm or more, becoming vinaceous brown with numerous seed-like concretions embedded in the jelly, 2) spores that are allantoid and colorless, and 3) basidia that are cruciate-septate and myxarioid. Klett(1) says that the presence of spheropedunculate basidia excludes this species from Exidia. The online Species Fungorum, accessed September 9, 2012, and August 30, 2017, gave this as a synonym of Myxarium nucleatum Wallr., Fl. crypt. Germ. (Norimbergae) 2: 260 (1833). However, MycoBank, accessed August 30, 2017, keeps them separate and synonymizes Myxarium nucleatum with Myxarium hyalinum (Pers.) Donk.
Microscopic: spores 10-11 x 4-4.5 microns, allantoid, colorless, white in mass, germinating by repetition; probasidia 8-12 x 6-8 microns, ovate, becoming cruciate-septate, (Martin), basidia are myxarioid [having a stem-like part separated by a wall from the spherical metabasidial part, as in Myxarium or Stypella]
Notes: Myxarium atratum is found in BC, MB, NS, ON, PQ, AL, AZ, CA, GA, IA, LA, OH, ME, MI, MN, NC, NJ, NY, VT, WI, and WV, (Ginns), and Panama, Brazil, Europe, Pakistan, and Australia, (Martin).
Habitat and Range
Habitat
on bark; decaying wood; wood with bark on; limbs; dead branches; branches without bark; stems; dead grape vine; Acer macrophyllum (Bigleaf Maple), Acer saccharum (Sugar Maple), Ampelopsis tricuspidata (Boston ivy), Aralia spinosa (Devils-walkingstick), Juglans regia (English Walnut), Magnolia fraseri (Fraser Magnolia), Populus tremuloides (Quaking Aspen), Quercus hypoleucoides (Silverleaf Oak), Quercus tomentella (Island Oak), Salix glauca (Grayleaf Willow), Salix nigra (Black Willow), Sambucus caerulea (Blue Elderberry), Tilia americana (American Basswood), Vitis aestivalis (summer grape), scuppernong grape, (Ginns), all year (Buczacki)