Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: foliose but usually erect, 3-7 cm in diam., loosely adnate, irregularly lobate lobes: irregular, elongate, partly tube-formed due to the inrolled margins, separate, 0.5-6 mm wide, 50-100 µm thick; apices: rotund, entire, forming corniculate tips (curling inwards), usually erect upper surface: brown to medium gray, usually dull but shiny apically, strongly wrinkled longitudinally, not isidiate internal anatomy: with upper and lower cortices consisting of a single layer of irregularly isodiametrical cells 5-12 µm in diam., internally with loosely interwoven chains of Nostoc and hyphae lower surface: light gray to brown, smooth, with scattered tufts of white hairs Apothecia: frequent, laminal, sessile, 0.1-0.6 mm wide disc: brown to red-brown, concave to plane margin: thalline, concolorous with the thallus or cream-colored, often wrinkled exciple: euparaplectenchymatous, 12-65 µm thick centrally hymenium: hyaline below and thinly brown above, 125-300 µm tall; paraphyses: unbranched, c. 1 µm wide, slightly inflated apically; subhymenium: pale yellow, 25-50 µm thick asci: cylindrico-clavate, 8-spored ascospores: hyaline, muriform, 5-9-septate transversely, 1-2-septate longitudinally, ellipsoid to subfusiform, 30-56 x 10-20 µm Pycnidia: not observed Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: usually on soil, on rock among mosses World distribution: Europe, eastern Asia, Australasia and west coast of North America Sonoran distribution: southern California from sea level to 1500 m. Notes: In its typical form Leptogium palmatum is unlike any other species in Leptogium, due to the horn-like lobes. In this respect it superficially resembles some Cetraria species, though young and small specimens may be quite difficult to distinguish from L. californicum, which normally has more divided, non-tubular lobes. In very damp habitats, L. palmatum tends to produce white, anchoring rhizohyphae and may then be taken for one of the regularly tomentose species, none of which has such narrow, tubular lobes.