Summary:
Sistotrema oblongisporum is a member of the Sistotrema brinkmannii group, described as follows, "Fruitbodies effuse, smooth or grandinioid; hyphae with clamps, walls hyaline; gloeocystidia absent; basidia urniform, normally with 6-8 sterigmata; spores less than 9 microns long, ellipsoid, subcylindrical, suballantoid, or subglobose, uninucleate (except for S. binucleosporum)", (Hallenberg, Latin name underlined). As a rule it is recognized from its thin, dense, grayish, smooth fruitbodies, in a characteristic way lining dead branches of hardwoods, especially branches 1-2cm thick, (Eriksson).

Microscopic:
SPORES (4.5)5-6 x 1.5-2 microns, "suballantoid with a more or less concave adaxial side", smooth, thin-walled; BASIDIA 15-18(22) x 4-6 microns, at first rounded-ovoid, "when mature urniform with a rounded basal part" and a cylindric neck, 3-4 microns wide, with a basal clamp connection, normally 6-8-spored; CYSTIDIA none; HYPHAE monomitic, 2.5-3.5 microns wide, with clamp connections; SUBHYMENIAL HYPHAE "richly branched into a dense tissue"; BASAL HYPHAE "straight, glued to the substrate, with sparse septa", (Eriksson), SPORES 4-5 x 1.5-1.8(2) microns, type "has slightly longer spores (5-6 microns) which are straight or only slightly bent", (Hallenberg)

Notes:
It is a common species in Scandinavia (Eriksson). There is cultured material from BC, Sweden, and Australia, (Hallenberg).