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Bulletin of the British Museum (Natural History)

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168 BRIAN JOHN COPPINS<br />

Thallus effuse, endoxylic to epixylic, or epilithic, forming a thin, whitish grey or greenish grey,<br />

uneven, sometimes weakly areolate crust; <strong>of</strong>ten appearing scurfy due to invasion by foreign<br />

fungi and algae. Phycobiont micareoid, cells 4-7 /xm diam.<br />

Apo<strong>the</strong>cia numerous, immarginate, convex to subglobose, <strong>of</strong>ten tuberculate, black, matt or<br />

slightly glossy, surface minutely roughened, 0- 1-0-25 mm diam, or to 0-4 mm diam when<br />

tuberculate. Hymenium 30-35 /xm tall, without a distinct upper part (epi<strong>the</strong>cium), dilute sordid<br />

olivaceous with dark olivaceous vertical streaks, K+ green intensifying, HNO3+ red. Asci<br />

clavate, 35-33x9-5-11 /xm. Spores oblong or ovoid-oblong, straight, (O-)l-septate, (7-)<br />

9-12-3x2-5-3-5 />im. Paraphyses numerous, <strong>of</strong> two types: p.p. hyaline throughout, evenly<br />

distributed, branched and <strong>of</strong>ten anastomosing, ra<strong>the</strong>r thin, 1-1-2 /^m wide, apices sometimes<br />

widening to 2 /am and sometimes with colourless, oily, refractive contents; p.p. broad, 2-3 /xm<br />

wide, mostly simple, grouped in small fascicles and <strong>of</strong>ten embedded in dense pigment.<br />

Hypo<strong>the</strong>cium 40-70 /xm tall, dark sordid olivaceous or olive-brown, K+ green intensifying,<br />

HNO3+ red; hyphae embedded in greenish gel-matrix but walls not deeply pigmented, c. 1-5-2<br />

/am wide, interwoven but becoming vertically orientated towards <strong>the</strong> hymenium and sometimes<br />

continuing in to it as fasciculate paraphyses; ascogenous hyphae with short swollen cells, to 5 /am<br />

wide. Excipulum indistinct and soon reflexed, sometimes evident in sections <strong>of</strong> young apo<strong>the</strong>cia<br />

as a hyaline or dilute sordid olivaceous, non-amyloid zone c. 20 /am wide; composed <strong>of</strong> radiating,<br />

much branched and anastomosing hyphae 0-8-1-5 /am wide.<br />

Pycnidia numerous but inconspicuous, ± immersed, 25-50 /am diam; walls sordid olivaceous<br />

or olive-brown, K-l- green intensifying, HNO3-I- red. Conidiogenous cells elongate-ampulliform<br />

to subcyUndric, 4—5-5x1-5-3 /am. Conidia (mesoconidia) short cylindrical, sometimes faintly<br />

biguttulate, 3-4-2x1-1-3 /am.<br />

Chemistry: Thallus K— , C— , PD— ; apo<strong>the</strong>cia sections C— ; no substances detected by t.l.c.<br />

Observations: Micarea olivacea differs from M. eximia in its less brightly coloured hymenium<br />

pigmentation that is not concentrated in <strong>the</strong> upper part, more numerous and broader paraphyses,<br />

shorter and slightly broader spores with rounded apices, and shorter mesoconidia. From<br />

M. nigella it can be distinguished by <strong>the</strong> complete absence <strong>of</strong> purple pigmentation in water<br />

mounts, more numerous and broader paraphyses, more elongate and 1-septate spores, and ±<br />

immersed (never stalked) pycnidia. M. olivacea is easily confused with epruinose forms <strong>of</strong><br />

<strong>the</strong> common lignicole Lecidea turgidula Fr., but that species has a dark green or olive-brown<br />

excipulum <strong>of</strong> conglutinated hyphae that do not separate in K, a paler hypo<strong>the</strong>cium, and a thick<br />

walled, large celled phycobiont with cells 12-16 /am diam. In addition, <strong>the</strong> conidia <strong>of</strong> L. turgidula<br />

are smaller, c. 3-3-5x1-5-1-8 /am. When on rock M. olivacea can be confused with M.<br />

tuberculata, but <strong>the</strong> latter has a more brightly coloured hymenium and hypo<strong>the</strong>cium, somewhat<br />

smaller spores, narrower asci, and a non-micareoid phycobiont with cells c. 5-10 /am when<br />

globose or up to 15 X 7 /am when ellipsoid . M. tuberculata has similar pycnidia and conidia , but its<br />

conidiogenous cells are more slender and about twice as long as those <strong>of</strong> M. olivacea.<br />

Habitat and distribution: M. olivacea is an apparently rare, but probably overlooked, species,<br />

being known from just two localities, both in Scotland. At <strong>the</strong> type locality it occurred on <strong>the</strong><br />

hard Ugnum <strong>of</strong> a stump by a conifer plantation; <strong>the</strong> collection contains no associate species. At<br />

<strong>the</strong> o<strong>the</strong>r locality it occurred with Rhizocarpon hochstetteri and Baeomyces rufus on shaded rock<br />

in a mature conifer plantation. Little more can be said <strong>of</strong> its ecology until it becomes better<br />

known, but I am inclined to believe that it is essentially a lignicolous species with a preference for<br />

hard lignum . If this is true <strong>the</strong>n care should be taken not to overlook it in <strong>the</strong> field for forms <strong>of</strong> <strong>the</strong><br />

common M. denigrata with a reduced thallus.

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