Toensbergia leucococca

Thallus crustose to subsquamulose, episubstratal, usually indeterminate, thick, forming small patches between other lichens or, more rarely, spreading irregularly up to 10 mm or more across, areolate, sorediate; prothallus usually as an indistinct pale greyish brown stain or, more rarely, distinctly brown, blue or blackish; areoles usually persistently discrete, rarely becoming contiguous or, very rarely, more or less imbricate, almost circular to irregular, often distinctly incised and constricted at the base (subsquamiform), occasionally tending to become raised at the edge, flat to convex, conspicuous, to 0.4 (–1.0) mm across, non-sorediate surface usually distinct, smooth, dull, greyish white, pale yellowish green or pale yellowish brown; in dried collections often becoming more distinctly yellowish brown or pink; soralia pale green to pale yellowish with a brown tinge (usually becoming distinctly yellowish brown in dried collections), occasionally distinctly aeruginose due to a pigment (fading in K, N+ brown) in the external soredia, usually marginal and ± labriform, sometimes laminal and more or less orbicular, or apical and more or less capitate, usually delimited; soredia mostly fine, 20–45 µm diam.; wall distinct; medulla distinct, white. Apothecia and pycnidia not known. Thallus and soralia C+ red, K+ yellow, KC+ red, P+ yellow, UV+ yellow (alectorialic acid).

The P+ yellow reaction separates it from similar-looking species of Trapelia or Trapeliopsis. Also similar to Pycnora sorophora, which also contains alectorialic acid, but that species forms an endosubstratal thallus with soralia bursting through the wood or, when well developed, small, rounded episubstratal areolae which are never lobed or subsquamiform and soon burst into soralia.