Rhizoplaca occulta

This is a morphologically variable crustose to placodioid lichen. Many thalli resemble typical R. melanophthalma with tightly attached, radiating lobes and a dark central disk, while others form loose, unattached cushions—so-called "vagrant" morphs—that roll about the substrate; the latter include material previously labeled Rhizoplaca cerebriformis and R. subidahoensis. Because both attached and vagrant forms share the same DNA signature, they are treated as a single polymorphic species.^[2]

Chemically the lichen is dominated by usnic acid, which imparts a yellow-green tint to the surface. It usually contains psoromic acid as a second major metabolite, together with minor amounts of constipatic, dehydroconstipatic, 2'-O-demethylpsoromic, and 2'-O-demethylsubpsoromic acids; dehydroprotocetraric acid appears sporadically. These compounds can aid identification when morphological traits overlap with closely related species. No single set of macroscopic characters is diagnostic, so a combination of chemistry and DNA data is the most reliable means of recognition.^[2]

Rhizoplaca occulta is known to occur only in the interior western United States. Confirmed collections come from high-elevation sites in Idaho, Nevada, and Utah, including the type locality at 3,150 m on basalt outcrops of Cave Mountain, Nevada. The lichen typically colonizes exposed, calcium-poor rocks such as basalt, granite, or schist within open pinyon–juniper woodlands, but vagrant cushions can also occur free on coarse soil. All verified specimens were gathered between roughly 2,500 and 3,300 m (8,200 and 10,800 ft) where insolation is strong, moisture is episodic, and winter snow persists for part of the year. The scattered records and limited sampling suggest R. occulta may be more widespread in suitable subalpine habitats of the Great Basin and northern Rocky Mountains, yet it remains under-documented because of its cryptic appearance and the need for molecular confirmation.^[2]