Both the genus and species were described as new to science in 1974 by the English mycologist Richard Dennis.

According to Dennis, Margaret Elizabeth Barr Bigelow suggested to him that the fungus might belong in the family Arthoniaceae, because of similarities to Arthothelium, a genus of bark-dwelling, lichen-forming fungi.

Although Tarbertia juncina is not lichenised, it does grow on the culm of Juncus (a genus in the rush family).

[3] The dark brown ascoma of the fungus forms a layer between 7 and 10 μm thick and extending four to five cells deep.

After the external layer sloughs off, it exposes a margin with black lobes and yellow ascus-forming tissue, ultimately resembling a tiny species of Coccomyces.