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Lepraria usnica Sipman |
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Nomenclatural data
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Biblioth. Lichenol. 86: 179 (2003); type: Singapore, Sembawan Park, on N-coast, 25 Nov. 2000, H. Sipman & B. C. Tan 46399 (B—holotypus, SINU—isotypus).
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Morphology
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Thallus crustose, leprose, with powdery appearance; greyish green with yellowish or bluish tinge; thin to thick, relatively soft; shape irregular or of obscure rosettes, usually up to 10 cm in diam.; margin diffuse or delimited, lobes sometimes present, irregular, mostly less than 0.5 mm wide, usually without a rim; cortex absent; medulla usually present, thin to medium, white to pale yellowish; areoles sometimes present on thick specimens; squamules absent; thallus surfaces without soredia absent, soredia abundant, mostly medium sized, 70-100 µm in diam., relatively densely packed; projecting hyphae usually absent; isidia-like structures absent. Photobiont chlorococcoid, usually 10-12 µm in diam.
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Chemistry
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Three chemotypes were distinguished in a detailed chemical survey by Elix (2006b): (1) usnic acid, zeorin, contortin (minor), placodiolic acid (trace), hopane-16ß,22-diol (major to minor), isousnic acid (minor to trace); (2) usnic acid, zeorin, contortin (minor), placodiolic acid (trace), isousnic acid ± (trace), roccellic acid ± (trace); (3) usnic acid, zeorin, contortin (minor), placodiolic acid (trace), isousnic acid (minor to trace), atranorin (minor), chloratranorin (minor). Additionally, Sipman (2003) reported 5-chloro-3-0-methylnorlichexanthone and 5,7-dichloro-3-0-methylnorlichexanthone as trace accessories. K–, C± yellow to orange, KC± yellow to orange, Pd–.
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Remarks
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Chemically similar taxa include L. coriensis, L. ecorticata, L. straminea, L. texta and L. leuckertiana that produce usnic acid and usually zeorin, but differ in the following aspects. L. ecorticata, L. straminea and L. texta have no lobes and L. straminea has corticate granules. L. leuckertiana is only obscurely lobed and has a cottony appearance with well developed medulla, additionally the soredia of L. leuckertiana are not well separated from one another. Lobes of L. coriensis are usually well developed (0.5-2 mm), round and with marginal rim; that species produces protodehydroconstipatic and constipatic acids (in variable amounts) and lacks contortin. The chemical differences between L. coriensis and more recent L. usnica were demonstrated by Elix (2006b). Some authors have raised the question of the distinctiveness of L. usnica (Orange & Wolseley 2005).
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Ecology and distribution
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Substrate and ecology: rock, bark, soil; shaded places. Distribution: Australia, Southeastern Asia, Sri Lanka, Southern Africa, Central and South America; tropical.
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