Bulletin of the British Museum (Natural History)

LICHEN GENUS MICAREA IN EUROPE 111
Map 1 Micarea adnata # 1950 onwards O Before 1950
Pycnidia usually present, white with hyaline walls, of two types: (a) immersed in areolae, c.
100-220 /xm diam, ostiole often widely gaping; conidia (macroconidia) markedly curved, often
sigmoid, sometimes faintly 3-5-septate, 21-55 xc. 1 (xm; (b) ± sessile, c. 50-100 ^tm diam,
ostiole not, or only slightly gaping; conidia (microconidia) narrowly fusiform-cylindrical,
5-7x0-5-0-7/am.
Chemistry: Thallus and apothecia C-l- red; t.l.c: gyrophoric acid.
Observations: M. alabastrites is morphologically and chemically very similar to M. peliocarpa,
and it could easily be dismissed as representing a pale, shade form of that species. Apart from the
complete absence of pigment from all its tissues, M. alabastrites is subtly different from M.
peliocarpa in having slightly larger apothecia and spores. Shade forms of M. peliocarpa are
usually sparingly fertile with scattered apothecia, whereas the apothecia of M. alabastrites are
almost invariably numerous, crowded and often confluent. My early doubts regarding the
distinction of these two species were dispelled by the collection, on several occasions, of M.
alabastrites with adjacent thalli of M. peliocarpa with blackish apothecia; the slight differences in
the sizes of apothecia and spores were confirmed with these collections. The two species also
differ somewhat in distribution and habitat; M. peliocarpa is widely distributed throughout
much of Europe on a wide range of substrata (tree trunks, mossy rocks peaty soil etc.); whereas
M. alabastrites has a hyperoceanic distribution and occurs on tree trunks (or on bryophytes
thereon) and occasionally lignum, but apparently never on mossy rocks or peaty soil.
In the recent checklist of British lichens (Hawksworth et al, 1980) I mistakenly placed