Usnea complecta Motyka s.l. Lich. Gen. Usnea Stud. Monogr. Pars Sys. 2: 404, 407 (1938). Usnea laevis var. implexa Müll.Arg., Hedwigia30: 225 (1891).
Type: Brazil. Minas Gerais, in summo monte Itacolumi, Schenck s.n. [holotype in G, seen; isotype in LBL, seen]. %C/M/A: 11.5/25.5/25.5. Chemistry: usnic and salazinic acid.
Description.Thallus erect-shrubby to sub-pendulous, with a soft touch; ramifications ±anisotomic dichotomous; trunk concolorous with basal branches or slightly reddish-brown, often with few annular cracks; branches ±irregular, slightly to strongly inflated on basal branches, terminal branches becoming thin and sinuous in well-developed thalli; lateral branches slightly to distinctly constricted at ramification, rarely not (terminal branches); maculae sometimes visible on cortex surface, faint and whitish; pseudocyphellae absent; papillae absent (see tubercles); tubercles usually abundant on branches, low and hemispherical, sometimes slightly elongated especially close to the base, becoming eroded at the tip (whitish); fibrils slender, scattered on branches; fibercles absent; soralia developing from tubercles on secondary and terminal branches, distinctly stipitate, remaining well-delimited and capitate at maturity; isidiomorphs short, usually scarce, never very abundant; cortex pruinose, opaque to slightly shiny in section, moderately thin, (5.5 –)6.5 – 8(– 8.5 %); medulla dense (hyphae visible individually), (27–)27.5 –32(–35 %); axis white to slightly pinkish, (16 –)22.5 –30(–31.5 %), with an A/M-ratio 0.5 –1; apothecia and pycnidia not observed.
Chemistry. Medulla with protocetraric, confumarprotocetraric and salazinic acid [K+ (golden-)yellow turning deep red, C–, KC–].
Notes. In Galapagos specimens of U. complecta are easily recognized by a thallus with slightly to distinctly inflated branches, covered by low and usually ±elongated tubercles, by a pruinose surface, and by distinctly stipitate and capitate soralia. The branches of most specimens are inflated and constricted at their ramification, but few specimens have barely inflated and constricted branches; these unusually compact morphotypes may be juvenile.
Usnea subcomplecta has similar tubercles, but distinctly differs in the plane soralia becoming circular, at maturity delimited by a thin cortical rim, and a trunk blackened below its first ramification. The species also has a slightly thicker cortex and axis, and it lacks protocetraric acid in its medulla. Both U. complecta and U. subcomplecta belong to a highly diverse group of closely related species, the U. jamaicensis-group. The type of U. jamaicensis Ach., however, bears apothecia and molecular studies will therefore be necessary to resolve how sorediate and fertile specimens are in fact related.
Throughout the Neotropics morphological variation in the group is enormous: specimens vary considerably in the degree of their branch inflation and how strongly the lateral branches are constricted. Cortex/medulla/axis-ratios (CMA-ratio) are also highly variable. This plasticity constitutes a considerable challenge for species delimitation in the group. The holotype of U. complecta is characterized by a ±isotomic-dichotomous branching pattern, it has ±regular branches that are not inflated, and the lateral branches are not constricted at their ramification points. Also, our CMA measurements of the holotype (11/24/30; A/M=1.2) differ slightly from the measurements presented here for specimens from the Galapagos. The holotype contains salazinic acid and only a trace of norstictic acid. The Galapagos specimens are all characterized by the presence of protocetraric with confumarprotocetraric acid. Moderate chemotypical variation in species of Usnea is not uncommon, as recently discussed by Truong et al. (2013a). It is possible that the Galapagos populations are in the process of diverging from their mainland relatives. Only a thorough analysis, ideally examining the entire U. jamaicensis-group with molecular tools, will ultimately elucidate whether Galapagos populations should be considered a separate species. Until then we prefer to treat the material here as part of U. complecta s.l.