Usnea wirthii
Description : Thallus pale-green, erect, to 3 cm long, isotomic dichotomous, moderately branched, branches divergent, with one single point of attachment; trunk concolorous, short, 2 mm long, straight. Branches cylindrical, tapering slowly; segments terete, cylindrical to slightly swollen; apices short, finely branching. Surface papillate, fibrillose, sorediate; without pseudocyphellae; cortex glossy, often with small red spots (×10 lens) [these may be hard to find under the hand lens and even the dissecting binocular]. Papillae verrucose, sparse to abundant, irregularly scattered. Fibrils short, 1–2 mm long, spinulose, few to absent, mostly on main and secondary branches. Soralia on apices and short branches, originating in cortex or from transverse cracks, superficial to excavate, solitary to confluent; soredia granular to isidiose. Medulla thick, very loose to dense, fibrous, yellow. Axis thin, straight, solid, yellowish. Apothecia rarely present.
Chemistry : Cortex K+ yellow→red, C−, KC+ red, Pd+ golden-yellow; containing usnic, stictic, salazinic, norstictic and/or psoromic acids.
N: Wellington (Mt Lees Reserve nr Palmerston North, Tararua Ra., Makara Peak, Wellington City [Darrell Wright, pers. comm.]). On canopy branches of trees and shrubs in lowland forest and coastal scrub. Known also from Europe, W North America, Baja California, Mexico and Chile (Clerc 1984b; McCune & Geiser 1997; Halonen et al. 1998; Tavares et al. 1998; Wright 2003).
?Cosmopolitan
Illustrations : Tavares et al. (1998: 189, figs 1, 2; 191, fig. 3; 193, figs 4, 5; 295, figs 6–9).
Usnea wirthii is characterised by: the small shrubby thallus (it is a member of the U. fragilescens agg.); inflated branches, wide, sparse, yellow medulla; thin glossy cortex, sometimes with minute purplish red spots; plane to excavate soralia with granular to isidiose soredia; and two chemodemes (containing either norstictic acid K+ yellow→red; or psoromic acid K−, Pd+ golden-yellow).
