|
|
Family: Parmeliaceae
|
Usnea mayrhoferi: MycoBank no. 825134 Diagnosis. Thallus erect-shrubby, branches not inflated, with abundant tubercles, fibercles and isidiofibrils, base blackish at the first millimeters, soralia irregular, becoming large and excavate at the branch apices, cortex mat, medulla very thin, axis very thick, with norstictic acid. Type: Ecuador. Galápagos, Isla Isabela, Volcán Sierra Negra, around the parking place at the end of the dirt road to the crater of Sierra Negra, 0°49.0'45.1''S, 91°5.0'17.1''W, 913 m alt., humid zone, farming areas, with small trees of Psidium guajava, slope 25° SE, on living fencepost, 14-Aug-2008, Clerc 08-213 [holotype in CDS (40067); isotype in G]. %C/M/A: 9/7/68. Chemistry: usnic and norstictic acid. Etymology. Named in honor of our good friend and colleague Helmut Mayrhofer, to whom this publication is dedicated on occasion of his 65th birthday. Description. Thallus erect-shrubby, compact and stiff; ramifications ±isotomic-dichotomous; trunk blackish on the first millimeters (below first ramification), often with thin annular cracks extending on basal branches; branches cylindrical to irregular in diameter, not inflated; lateral branches not constricted at ramification; maculae absent; pseudocyphellae absent; papillae absent to sparse (see tubercles); tubercles typically abundant, hemispherical to verrucose, little eroded; fibrils slender, scattered to abundantly distributed on branches; fibercles absent; soralia developing on the cortex of terminal branches, plane to slightly stipitate, minute and aggregating in irregular clusters at young stage, at maturity becoming large and excavate (almost efflorescent) on the apices of branches; isidiomorphs usually abundant, developing into isidiofibrils within soralia and from eroded tubercles on basal and secondary branches; cortex opaque, moderately thick, (7.5 –)8.5 –12.5(–13 %); medulla compact to dense (hyphae visible individually), very thin, (5.5 –)8 –12(–12.5 %); axis white, very thick (52.5 –)53 – 65(–73.5 %), with an A/M-ratio > 4.5; apothecia and pycnidia not observed. Chemistry. Medulla with norstictic acid only [P+ yellow, K+ yellow turning orange-red (crystals), C–, KC–]. Ecology and distribution. Usnea brattiae, U. cedrosiana, U. mayrhoferi, U. krogiana and U. patriciana all form a group of similar and possibly very closely related species, which apparently differ in their distribution. Usnea brattiae and U. cedrosiana are known from Southern California and the Isla Cedros, U. krogiana from the Azores, the West Indies and possibly from the Galapagos, and U. mayrhoferi and U. patriciana are currently known only from the Galapagos. Compared to most other species of Usnea in the Galapagos U. mayrhoferi is ecologically somewhat unusual: all specimens have Notes. Usnea mayrhoferi is characterized by a stiff and compact thallus with non-inflated branches bearing abundant tubercles, fibrils and isidiofibrils. It has a distinctly blackened trunk (below the first ramification), bearing annulations all along its basal branches, and irregular, crowded soralia, becoming large and excavate at the branch apices. The species has an opaque cortex and a very broad axis (A/M-ratio > 4.5). The new species much resembles U. krogiana P.Clerc, described from Macaronesia, also reported from the West Indies (Clerc 2006). The protologue of U. krogiana cites different chemotypes, and although the one with stictic and norstictic acid is most commonly found, a chemotype with norstictic acid only has also been reported. Usnea mayrhoferi can therefore not necessarily be distinguished by its chemistry, but the two species clearly differ in their soralia. Soralia of U. krogiana are punctiform and not delimited by a distinct rim. They are generally slightly stipitate, arise from tubercles, and although they are numerous and frequently closely grouped, they typically do not merge. Usnea mayrhoferi has soralia that are generally much larger, not distinctly punctiform, but irregular in outline. They are inconspicuously delimited and particularly towards the branch apices typically merge, thus obscuring the tip of the branches, occasionally becoming deeply excavate. Usnea brattiae P.Clerc from the Sonoran region (the Channel Islands of Southern California and Isla |