Bulletin of the British Museum (Natural History)

LICHEN GENUS MICAREA IN EUROPE 115
± vertically orientated near the hymenium, c. 1-7-2-7 fxm wide, embedded in a densely
pigmented matrix; ascogenous hyphae c. 1-7-2-7 /xm wide, embedded in a densely pigmented
matrix; ascogenous hyphae c. 2-5-5 fxm wide. Excipulum reflexed, mottled reddish brown or
sordid olivaceous; hyphae radiating, branched and anastomosing, 1-5-2 /xm wide.
Pycnidia rare, semi-immersed to sessile, black, 40-100 /^m diam; walls dull reddish brown, or
dull olivaceous in part; conidia (? microconidia) cylindrical, 6-9x1-1-5 /xm.
Chemistry: Thallus K— , C— , KC—
, PD — ; t.l.c: no substances.
Observations: Micarea assimilata is characterized by its conspicuous, whitish, verrucose
areolae which are often intermixed with brown cephalodia, rather large, convex, black
apothecia, green (K— ) epithecium, dark purple-brown hypothecium and predominantly simple,
large spores. It is apparently closely related to M. crassipes, M. incrassata, M. melaenida, and M.
subviolascens , all of which share rather stout, simple or sparingly branched paraphyses, rather
stout excipular hyphae, dark hypothecia and an absence of lichen substances. In many ways M.
assimilata is identical to M. incrassata and both occur in similar habitats; indeed the latter has
often been considered a variety (var. infuscata) of the former (e.g. Anderson, 1964; Hertel,
1977). However, M. incrassata differs in several respects, the most important of which is its quite
different, red-brown hypothecium which lacks any trace of purple pigmentation in water, K or
HNO3. In addition, it has an often darker thallus, less prominent apothecia and a generally
higher proportion of septate spores. M. subviolascens is similar in appearance to M. assimilata,
but grows on rock and has a green, K-l- violet epithecial pigment. M. melaenida differs from the
last three species in its comparatively small apothecia and less conspicuous thallus, absence of
green pigmentation in apothecial tissues, preponderance of 1-septate spores, shorter conidia,
and confinement to argillaceous, or fine-grained, mineral soils. M. crassipes occurs in much the
same habitats as M. assimilata and the two species have been much confused. However, M.
crassipes is easily distinguished by its apothecia which are thinly marginate (at least when young)
and markedly constricted below, often being turbinate or even short-stipitate; also by its thallus
which is composed of small granular-areolae which sometimes proliferate to give it an isidiose
appearance. In section, the apothecia of M. crassipes display a well-developed excipulum and a
distinctly two-zoned hypothecium.
Pycnidia are rare and difficult to find in members of the M. assimilata group, and have not yet
been found at all in M. subviolascens. The remaining species appear to have one conidium type
only; although the conidia are rather large, they afe probably microconidia. However, the
relatively shorter and broader conidia of M. crassipes may be better described as mesoconidia.
Cephalodia are here reported from M. assimilata and M. incrassata, apparently for the first
time. In both cases the blue-green alga concerned is Nostoc, which loses its filamentous form. In
addition, irregular clusters of partially disrupted Stigonema filaments are sometimes present
amongst the areolae of M. assimilata, M. incrassata, and also M. subviolascens. Hyphae,
presumably belonging to the lichens, are seen to ramify through these clusters; but whether or
not these loosely organised structures can be considered to be cephalodia is a problem requiring
further detailed anatomical and experimental investigation. Cephalodia or cephalodia-like
structures have not been encountered in any other Micarea species.
The closely related Lecidea limosa Ach. and L. stenotera (Nyl.) Nyl. have often been confused
with M. assimilata and M. incrassata, but they can be distinguished by their pale hypothecia,
paraphyses which are individually supplied with a dense, hyaline, gelatinous sheath, and more
organised excipular structure. Together with Catillaria contristans (Nyl.) Zahlbr. they probably
represent a distinct genus within the Lecideaceae, although perhaps not far removed from
Micarea. In British herbaria (at least) there has been much confusion between M. assimilata and
Lecidea hypnorum Lib. The latter has marginate, brown-black apothecia, simple paraphyses,
0(-3)-septate spores which become straw coloured and finely warted with age, a reddish brown
excipulum composed of radiating, stout, pachydermatous, heavily conglutinated hyphae, c.
3-5 /xm wide, and bears little resemblance to a Micarea. In addition, the hymenium, hypothecium
and excipulum of L. hypnorum (and the related L. berengeriana (Massal.) Th. Fr. , and L.
sanguineoatra auct.) often contain minute granules of a dark violet (K-l- aeruginose) pigment.