The
thallus of
Xanthoparmelia alligatensis is
foliose, loosely adnate to the , and can reach up to 8 cm in diameter. Its are separate to slightly overlapping (), measuring 1.5–3.5 mm in width, with more or less linear to somewhat irregular shapes that can form branches. The lobe tips can be either more or less round or incised. The upper surface of the thallus is initially grey to grey-green and darkens as it ages, becoming flat to weakly convoluted, dull, and in the centre while remaining shiny and black-margined at the lobe tips. The surface lacks
soredia and
isidia, which are structures involved in reproduction and dispersal. The lower surface is smooth, ranging from ivory to brown, and darker towards the lobe tips.
Rhizines (root-like structures beneath the lichen) are sparse, short, slender, and colour-coordinated with the lower surface. Reproductive structures are limited to somewhat stipitate
apothecia (fruiting bodies), which are 1–7 mm wide, with a mid-brown to dark brown . The lichen produces
ellipsoidal ascospores measuring 9–12 by 5–6
μm. ==Chemistry==