Bulletin of the British Museum (Natural History)

LICHEN GENUS MICAREA IN EUROPE 141
richly branched, not or only slightly incrassate (to 1-8 /xm wide) and without closely adhering
pigment (epithecial pigment confined to surrounding gel-matrix). Hypothecium c. 35-45 txm
tall, but becoming much taller in markedly convex or tuberculate apothecia, dilute straw- or
fuscous-brown, pigment confined to gel matrix; hyphae interwoven, but becoming outwardly
orientated towards the hymenium and excipulum, c. 0-8-1-5 /u,m wide; ascogenous hyphae with
swollen cells, c. 2-6 /am wide. Excipulum distinct in young, moderately convex apothecia, but
reflexed and obscured in subglobose or tuberculate apothecia, dilute fuscous brown (K— );
hyphae radiating, branched and anastomosing, c. 0-5-1 -5 /u,m wide.
Pycnidia not found.
Chemistry: Thallus K-, C+ red, PD-I- red; apothecia in section C-l- red; t.l.c: argopsin and
gyrophoric acid.
Observations: M. leprosula is characterized by its sterile or sparingly fertile, granular thallus
composed of blue-grey (or brown-grey), fragile areolae which often dissolve (or become
abraded) to form contrasting, yellowish green, sorediose patches. These characters are shared
by the much rarer M. subleprosula, and the thalli of both react C+ red. However, M.
subleprosula can be separated by the PD-I- yellow reaction of its thallus due to the presence of
alectorialic acid. When fertile M. subleprosula is found to have much larger, mostly 7-septate
spores. M. leprosula is usually distinctive in the field (although material should always be
checked with M. subleprosula in mind) but can easily be overlooked when it occurs on
bryophytes on shaded rocks or trees, whence the thallus often lacks its characteristic bluish tinge
and the areolae are thinly scattered. The species is usually sterile but fertile specimens are
occasionally encountered, especially in sheltered (but not deeply shaded) situations, such as on
boulders and old walls in woodland.
Hedlund (1892) regarded M. leprosula as a variety of M. peliocarpa (q.v.) and the apothecia
of the two species are somewhat similar. However, those of M. leprosula exhibit several minor,
yet significant, differences; spores tend to be slightly longer; apothecia tend to be more
markedly convex and more frequently tuberculate; hypothecium and excipulum are dilutely
pigmented with a dull brown pigment; and paraphyses never become thickened and pigmented
at their apices. The two species also differ in several fundamental aspects of thallus morphology
and chemistry. With regard to the production of argopsin and to the presence of a dull brown
pigment in the excipulum and hypothecium M. leprosula shows some affinity to M. lignaria var.
lignaria, with which it often occurs. However, M. lignaria lacks gyrophoric acid, has usually
longer and more septate spores, and somewhat stouter and only sparingly branched paraphyses.
The areolae of M. leprosula and M. subleprosula differ from those of such species as M. lignaria,
M. peliocarpa, and M. cinerea, in lacking an amorphous hyaline covering layer (see 'morpho-
logy')-
Habitat and distribution: M. leprosula is widely distributed in upland areas in the north and
west of Britain, occurring at altitudes from about sea-level to at least 1100 m. It is found, usually
on moribund bryophytes (e.g. Andraea spp. and Rhacomitrium spp.) on rocky ledges, boulders,
and old walls, in exposed hilly areas, mountain sides or woodlands. Associated lichens noted
amongst British collections include Arthrorhaphis citrinella, Baeomyces rufus, Belonia incar-
nata, Cladonia cervicornis, C. coccifera, C. crispata, C. portentosa, C. squamosa, C. subcervicornis,
Coelocaulon aculeatum, Lecidea granulosa, L. icmalea, Lepraria neglecta, Micarea
lignaria, M. peliocarpa, and Vorarlbergia renitens. From Scotland I have seen two corticolous
specimens, on trunks of Alnus and Betula; associated species present included Cladonia
coniocraea, C. squamosa, Lecidea icmalea, Micarea melaena, and Platismatia glauca.
There are two outlying localities in the lowlands of southern England. In Dorset it occurs on
waste heaps of slag clay with M. lignaria (q. v.); and in Kent it was found with M. peliocarpa on
wood chips lying at the side of a woodland track in a chestnut (Castanea) coppice.
M. leprosula is poorly recorded outside Britain, probably because it is so often sterile. To
date, I have seen one specimen from Norway (Hordaland) and several collections from mid- and
southern Sweden. Further south it seems to be well represented in the Alps, and I have seen one