Bulletin of the British Museum (Natural History)

LICHEN GENUS MICAREA IN EUROPE 175
material has not been located in BM but it could be elsewhere (? G). Under the taxonomic arrangement
given here Zwackh's epithet is of no consequence. If the chemical races of M. prasina were to be awarded
varietal status, then under the provisions of Article 72 the name ' Catillaria prasina p. [var.] byssacea Th. Fr.
(1874)' could become important and require typification. If this name was typified with a specimen
containing 'prasina unknown A' then it would be the earliest available name at that rank.
Thallus effuse and often wide-spreading, very variable in colour, pale fawn (dry shaded
situations), light green, pale to dark grey-green (often with glaucous hue), or olivaceous to
olive-black, often appearing ± gelatinous when moist, composed of small ± globose granules
(goniocysts). Goniocysts c. 12^0(-60) jxm diam, thinly scattered, or vertically proliferating to
give the thallus a soft isidiose appearance, or densely aggregated to form a thick granular crust
up to 200 />tm deep. Goniocysts ecorticate, often with shortly protruding hyphal filaments;
outermost hyphae of superficial goniocysts sometimes surrounded by greenish, K+ violet
pigment. Phycobiont micareoid, cells 4-7 ^tm diam.
Apothecia usually numerous but sometimes few or absent, immarginate, sometimes adnate
and shallow-convex, but more usually becoming markedly convex, subglobose or tuberculate;
colour variable, whitish or pallid {'micrococca' shade-forms), pale to dark grey, brownish grey,
or grey-black, matt; 0- 1-0-4 mm diam, or to 0-6 mm when tuberculate. Hymenium 28-45(-52)
H^va tall, hyaline or dilute dull straw, but more usually dull olivaceous, especially in the upper
part (but coloured portion not sharply delimited) or in vertical streaks; pigment K+ violet,
HNO3+ red, confined to gel-matrix. Asci clavate or cylindrical-clavate, 26-40(-50)x8-12 /u,m.
Spores ovoid-ellipsoid, ovoid, ovoid-oblong or oblong, 0-l(-3)-septate; when 1-septate the
lower cell is slightly longer and narrower than the upper, and there is often a slight constriction at
the septum; variable in size, in range 8-14(-17)x2-3-4(-5) /xm. Paraphyses rather numerous,
branched and anastomozing, 0-5-1 /xm wide; apical parts often wider, to 1-5 /xm, but not
thickened by pigment; epithecial pigment confined to surrounding gel matrix. Hypothecium c.
40-170 /xm tall, hyaline to dilute dull yellowish; hyphae interwoven, some becoming vertically
orientated towards the hymenium, c. 0-7-1-3 jxm wide; ascogenous hyphae with swollen cells, c.
2-4 /xm wide. Excipulum poorly developed, sometimes evident as a narrow, hyaline or dilute
olivaceous-straw (K-l- violet), non-amyloid, reflexed zone; hyphae radiating, branched and
anastomosing, c. 0-7-1 /am wide.
Pycnidia often present but usually inconspicuous, white, or upper part around the ostiole grey
(due to olivaceous, K+ violet pigment), immersed to sessile (never distinctly stalked), of two
types: (a) c. 50-120 /xm diam, emergent to sessile, ostiole sometimes gaping; conidia (mesoconi-
dia) ± cylindrical or narrowly obpyriform, often biguttulate and slightly constricted near the
middle, (3-5-)4-6x 1-2-1-7 /xm; (b) c. 30-60(-100) /xm, usually immersed in surrounding
goniocysts, ostiole rarely gaping; conidia (microconidia) cylindrical or narrowly fusiform,
(5-)5-5-8x0-7-l/xm.
Chemistry: All parts K— , C—
(but olivaceous pigment C-l- violet, never red), PD— ; t.l.c:
specimens have one of three unknowns ('prasina unknown A', 'B', or 'C; see p. 87); trace
amounts of gyrophoric acid sometimes detected, possibly due to contamination by intimately
associated species such as Lecidea icmalea and L. granulosa agg.
Observations: Micarea prasina is the commonest and most variable member of the genus.
However, it is one of the few European species whose thallus is composed of minute discrete
granules (goniocysts). Two other species with a similar thallus are: M. hedlundii (q.v.) with a
K-l- red oily substance in the goniocysts and conspicuous tomentose, brown, stalked pycnidia;
and M. melanobola which has a sharply delimited epithecium (pigment closely adhering to
apices of the paraphyses) and shorter microconidia . Both of these species appear to be very rare
A comparison of the diagnostic features of M. melanobola, M. prasina and M. misella are given
in Table 6.
Diminutive forms of M. prasina with small pallid apothecia and a scanty thallus have
sometimes been regarded as a distinct species {'Catillaria micrococca') .
Such forms have the
same basic thallus structure, spores, paraphyses, anamorphs and chemistry (with either 'prasina
unknown A' or 'B') as more typical forms (with coloured apothecia and more robust thallus).
.