Candelariella clarkiae is distinguished from other members of the genus by its chartreuse thallus (rather than egg-yolk yellow), along with other chemical and morphological differences (Tripp & Lendemer 2015).

Candelariella clarkiae, so far as is known, is an extremely rare species restricted to soft sandstones of the Colorado Front Range and Utah in the arid American SW.

So far as is known, Candelariella clarkiae is found from one location each in the grasslands and aridlands of Colorado, Iowa, and Utah, for a total of three locations. Its EOO is 37,888.371 km2 and its AOO is 12 km2. Most of its known range is on private land, where it is threatened by agriculture, livestock grazing, and development, thus its area of suitable habitat is inferred to continually decline into the future, qualifying the species for EN under criterion B2ab.

Candelariella clarkiae is known from at least three mature individuals from three locations across Iowa, Colorado, and Utah. Because of its easily overlooked nature and a general lack of lichen collecting in continental North America, it is likely to be overlooked/undiscovered elsewhere. Extensive general floristic-style collection efforts near the type locality in Boulder Colorado and throughout Colorado has failed to recover more populations, suggesting that the species is truely rare. It is not likely to be represented by more than 250 mature individuals in the wild, thus qualifying it for EN (criterion D).

It appears to prefer sandstones in exposed habitats in arid continental climates of the central and western US with temperate grassland (4.4) and temperate desert (8.2) vegetation.

Throughout much of its range, Candelariella clarkiae is threatened by development (1.1, 1.2), cattle grazing (2.3.4), and agriculture (2.1.4). This is because much of its suitable habitat lies on private land.

Some of its populations are on preserved land (1.1), but most of its suitable habitat is likely found on privately-owned land where the species is not protected.

More collection/survey efforts are needed to understand ecological niche requirements (1.3) and population size (1.2) of Candelariella clarkiae.

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