Usnea cornuta Körb.

    Thallus tufted, erect, 3-6 cm tall or, but more rarely, subpendulous, 5-10 cm long. Main branches not blackened at the base, often inflated, flexible and not easily breakable, lateral branches clearly constricted and often with white rings at the point of attachment to the main stems, also with fibrils at right angle, ladder-like notably towards the apices with stag horns-like endings, cortex glossy, smooth but often with isidiomorphs mixed with white punctiform soralia, medulla white. Overall colour olive-green, green-bluish, green-yellowish, grey-yellowish in humid weather, yellowish-gray, gray, in dry weather possibly red-orange when old in some places due to alteration. Infertile. Photobiont: trebouxioid. Two chemotypes are known: a) medulla : C-, K+ yellow > red, Pd+ yellow to yellow-orange ; b) médulle : C-, K+ yellow > blood red, Pd+ yellow-orange. Quite common, on mossy branches of deciduous trees in humid woodlands (notably Salix), less frequently on mossy rocks in ancient humid woodlands or forests.

N.B. Old altered specimen (notably fallen down on the ground) that to some extent turn to red-orange may easily be confused with Usnea rubicunda, but in this species the whole cortex is characterized by a more intense red.