Both the genus and species were described as new to science in 2021 by Daphne Stone, Bruce McCune, and Jolanta Miądlikowska.

The type specimen was collected by the first author from Polk County, Oregon (USA), where it was found growing on the soil.

The lichen has a minute fruticose (bushy) grey to almost black thallus.

The genus name Sinuicella refers to the cortical cells with curved protrusions in their outlines, somewhat resembling jigsaw puzzle pieces.

The specific epithet denisonii honours mycologist William C. Denison, who was, according to the authors, "a pioneer in the use of lichens to monitor air quality in the United States.