The lichen forms a small leaf-like to somewhat crust-like (
crustose) structure that clings closely or very closely to its surface, growing to 4 cm in width. Its are separate or rarely touching, somewhat linear to elongated-linear in shape, branching in patterns that fork into two, measuring 0.3–1.0 mm wide, with notched tips. The upper surface is pale yellow-green when young (darkening as it ages), flat, initially shiny but becoming dull, smooth or slightly wrinkled (), developing cracks across its width as it ages and breaking into small areas () in the center. The surface lacks powdery reproductive structures (
soredia) but has small projections () with rounded to short cylindrical finger-like growths (
isidia) that are simple with fused outer layers, blackened, intact tips. The inner layer (
medulla) is white, while the lower surface is flat, smooth, brown with darker brown at the tips. The root-like attachments (
rhizines) are moderately dense, sturdy, simple, matching in colour, and 0.1–0.4 mm long.
Xanthoparmelia stuartioides is characterised by its adnate to tightly adnate, small-foliose to somewhat crustose thallus, narrow separate lobes with incised (notched) tips, brown lower surface, simple subglobose to short-cylindrical
isidia, and its medullary chemistry. It contains
usnic acid (minor),
protocetraric acid (major), and
virensic acid (trace). While
X. stuartioides resembles
X. stuartensis in having a brown lower surface, an isidiate upper surface, and identical medullary chemistry, it differs in having a smaller thallus with narrower (0.3–1.0 mm vs. 1–3 mm), somewhat linear to elongated lobes with incised tips rather than the broader, irregular lobes with subrotund apices found in
X. stuartensis. ==Habitat and distribution==