Placopsis trachyderma var. clavifera (I.M.Lamb) P.James
P. alphoplacoides var. clavifera Lamb, Lilloa 13: 236 (1947).
As for P. trachyderma, but with terete, simple or branched isidia, and with pycnidia in thalline verrucae. Conidia filiform, curved, 12-16 × 0.5 µm.
P. trachyderma var. clavifera has a similar range of distribution to P. trachyderma but is most commonly found on glacial or river silt and gravel where it forms spreading rosettes to 10(-20) cm diam. The often extensive tartareous crusts appear to be of importance in soil consolidation, for when lifted from the soil many small pebbles always adhere to the thallus.
