Umbilicaria nodulospora

The thallus of Umbilicaria nodulospora is either monophyllous (single-leafed) or polyphyllous (multiple leaves), growing up to 2–3 cm (0.8–1.2 in) in diameter and about 0.2 mm thick, excluding the rhizines. It features a brown to gray-brown upper surface that is faintly to distinctly pruinose (powdery), creating a grayish effect especially near the central attachment point (umbo). The texture is smooth to broadly cracked in a network pattern (reticulation), facilitating the thallus splitting into partial thalli. The edges may be whole to irregularly torn or lobed.^[3]

The lower surface varies from brown to black, often covered with a dense mat of rhizines—hair-like growths that anchor the lichen to its substrate. These rhizines can be parallel or entangled, contributing to a mat that is 1–2 mm thick. The apothecia (fruiting bodies) are black, sessile (directly attached), and can be up to 2 mm in diameter, typically showing a gyrose (brain-like) surface. The spores are simple and hyaline (translucent), and characterized by having one or two blunt, shallow knobs at one end, giving them a T, Y, or L shape.^[3]

Umbilicaria nodulospora is known from geologically recent flood basalts in central Oregon to northeastern California. It inhabits steeply inclined surfaces of these basalt flows, typically found in cooler, north-facing areas. The specific ecological adaptations that allow it to thrive in such niches are not fully understood, though its occurrence on basalt is a key aspect of its habitat preference.^[3]