Filaments of Trichormus fertilissimus form dense mats that appear blue-green or olive green. The trichomes are slightly curved and cylindrical, with slight constrictions at the cross-walls. The cells themselves are cylindrical, ranging from blue-green to grey-blue in color, and are generally either isodiametric or longer than they are wide, measuring 1.6–7 µm in length and 2.2–3 µm in width. Terminal cells are typically conical or cylindrical with rounded ends. Heterocytes, specialized cells for nitrogen fixation, are ovoid to cylindrical and also have rounded ends, measuring 4.8–8 µm in length and 2.8–4.5 µm in width. Akinetes, which are resting spores, are oval cylindrical and solitary or up to three in a row, ranging from 12–36 µm to 7–11.5 µm in size, and have a smooth, brownish exospore. This species is commonly found in wet soils, sometimes among mosses and in pools with sandy bottoms.