Usnea undulata
Description : Thallus shrubby, erect or decumbent, 5–10(–13) cm tall, grey-green, cortex usually glossy; pale at base, branching subdichotomous to irregular. Branches terete, 0.5–1 mm diam., apices tapering; branchlets few to numerous; fibrils dense, rarely sparse, 1–5 mm long; papillae absent; isidiate, pseudocyphellate. Isidia dense on cortex of main branches and in pseudocyphellae if present, cylindrical becoming pustulate. Pseudocyphellae evenly distributed, sparse on primary branches, more numerous to dense on secondary and terminal branches, punctiform, elongate or orbicular, flat to raised. Soredia absent. Medulla moderately dense, ¼ –½ the width of branch, hyaline. Apothecia not seen.
Chemistry : Thallus K+ yellow→orange-red; containing norstictic, salazinic, galbinic and usnic acids.
S: Marlborough (d'Urville I.). On rocks in grassland; elsewhere in its known range it grows on fenceposts, trees and shrubs in open woodland or scrub. Known also from Madeira, East Africa, South Africa and Australia (Swinscow & Krog 1975c, 1988; Stevens 1999, 2004b; McCarthy 2003c, 2006).
?Pantropical
Illustrations : Swinscow & Krog (1975c: pls 1, 2; 1988: 345, fig. 179); Stevens (1999: 105, fig. 68).
Usnea undulata is characterised by: the saxicolous (though generally corticolous elsewhere) habit; the shrubby, erect or decumbent, grey-green thallus; irregular to subdichotomous branching; terete branches, 0.5–1 mm wide and tapering apically; an absence of papillae and soredia; presence of pseudocyphellae, especially on secondary and terminal branches; a dense development of isidia on cortex and in pseudocyphellae, the isidia cylindrical to pustulate; and salazinic, norstictic and galbinic acids (K+ yellow→red) in the medulla.
