Appin, A i'g jll; Ben-y-Gloe, Ben Lawers and Craig Tulloch, Blair
Athole, Perthshire ; Canlochan, Forfarshire ; Craig Guie and Morrone,
Braeniar, Aberdeenshire; Portinarnook, near Dublin.
9. Rh. petrseum Massal. Bic. Lich. p. 102 (1852) (non
Koerb.).—Thallus white or greyisli-white, orbicular, determinate,
thin, wrinkled or almost smooth, subcontinuous or cracked-
areolate, sometimes thin and almost disappearing (K —, CaCl — ,
I —) ; hypothallns evanescent. Apothecia black, small, usually
growing in concentric lines, appressed or subinnate, somewhat
concave or plane, marginate, the margin thick and often
white-pruinose; hypothecium blackish-brown; spores oblong,
muriform, colourless or slightly brownish, halonate, 0,025-44 mm.
long, 0,011-17 mm. th ick ; hymenial gelatine deep-blue with
iodine.—Lichen petrseus Wulfen in Jacquin Collectan. Botan. iii.
p. 116, t. 6, f. 4 (1789). L. concentricus Davies in Trans. Linn.
Soc. ii. p. 284 (1794); Engl. Bot. t. 246 ; With. Arr. ed. 3, iv.
p. 18. Lecidea petrsea Ach. Meth. p. 37 (1803); S. E. Gray Nat.
Arr. i. p. 463 ; Hook, in Sm. Engl. El. p. 175 ; Tayl. in Mackay
El. Hib. ii. p. 117 pro p a rte ; subsp. concentrica Nyl. Lich.
Scand. p. 234 (1861); Cromb. Lich. Brit. p. 87. L. concentrica
Leight. Lich. El. p. 349 (1871); ed. 3, p. 378. Ehizocarpon
petrseum var. concentricum Mudd Man. p. 220 (1861).
Exsicc. Leight. n. 17 ; Johns, n. 355.
The specific name petrmum has been given by later British authors
to forms now included under Sh. confervoides, but Wulfen’s description
and figure of Lichen petrmus undoubtedly represent this species
with its concentrically arranged apothecia, and his name takes precedence
of the more characteristic concentricus of Davies. Sometimes
it is regarded as only a variety of the preceding species, but is easily
recognized and differentiated, even when the thallus is almost evanescent,
by the peculiar lines formed by the contiguous apothecia.
Leighton’s f. typica (Lioh. FL ed. 8, p. 378) is a condition in which
the thallus is well developed and almost continuous ; in f. impressula
Leight. and f. coarctata Leight. (L c. p. 379) the apothecia are more
concave and at times oiroumscissed; in the latter the thallus is also
diffuse or scattered. The spermogones are not uncommon, the spermatia
rod-shaped, 0,006 mm. long, 0,0006 mm. thick.
Hah. On rooks, chiefly calcareous, more rarely schistose and
arenaceous.—Distr. Frequent in maritime and upland regions.—
B. M. Wadebridge, Cornwall; near Beeding and Sullington Heath
Sussex ; Ullacombe, Dartmoor, Devon; Leith Hill, Surrey; Wickwar
Gloucestershire ; Malvern Hills, Worcestershire ; near Ledbury, Here
fordshire; Oswestry, Shropshire ; Cader Idris and Dolgelly, Merioneth
Capel Cui-ig, Carnarvonshire ; Llangollen, Denbighshire; I. of Angle
sea ; Bilsdale, Cleveland, Yorkshire ; Pentland Hills, near Edinburgh ,
near Balmerino, F ife ; Baldoran, Forfarshire ; Glen Loohay, Killin,
Perth sh ire ; Killarney, Kerry.
Var. excentricum A. L. Sm. (non Boist. Nouv. El. Lich. pt. 2,
p. 240 (1902).—Thallus whitish, effuse, less developed th an in
the species, sometimes almost evanescent. Apothecia numerous,
scattered irregularly over the thallus, rarely in indistinct lines,
sometimes innate and circumscissed as in the species.—Lecidea
petræa var. excéntrica Ach. Meth. p. 37 (1863) ; subsp
excéntrica Nyl, Lich. Scand. p. 234 ; Oromb. Lich. Brit. p. 87.
L. concéntrica var. excéntrica Leight. Lich. PI. p. 350 (1871).
L . excéntrica Leight. Lich. El. ed. 3, p. 379 (1879).
Exsicc. Larb. Lich. Hb. n. 75; Mudd n. 194 (as Diplotomma
calcareum).
Hah. On calcareous rocks.—EZsZr. Somewhat rare throughout
the Bntish Isles.—A. M. Jersey; Builth, Brecknockshire; Llany-
myneoh, Shropshire ; Dolgelly and Cader Idris, Merioneth ; Carlton
Bank, Cleveland, Yorkshire ; Achosragan Hill, Appin, Argyll ;
Morrone, Braemar, Aberdeenshire.
10. Rh. confervoides DC. PL Franc, ii. p . 565 (1805)
emend, (non Massal.).—Thallus subdeterminate or effuse, often in
small patches, greyish-white or -brown, finely areolate, the
areolæ contiguous or dispersed, convex or depressed, on a thin
black spreading often fimbriate hypotballus. Apothecia numerous,
moderate in size, black, innate-sessile, plane, with a th in margin ;
hypothecium thick, brownish-black; paraphyses stoutish, lax,’
clavate and greenish-brown a t the tips ; spores oblong, ovate or
ellipsoid, a t first colourless, becoming dark-coloured, halonate,
irregularly muriform, 0,020-38 mm. long, 0,010-17 mm. th ic k ;
hymenial gelatine blue with iodine.—Eli. petrseum Koerb. Syst.
Lich. Germ. p. 260 (1855) pro parte (non Massal.) ; Mudd Man!
p. 220 (excl. vars.). Lecidea petrsea Tayl. in Mackay PL Hib. ii.
p. 117 (1836) pro parte ; Plot, ex Nyl. in Act. Soc. Linn. Bord.
ser. 3, i. p. 374 (1856) (excl. vars.); Cromb. Lioh. Brit. p. 86
(excl. vars.) ; Leight. Lich. El. p. 347 ; ed. 3, p. 375. L. amphibia
Pr. Lich. Eur. p. 307 (1831) fide Nyl. Lich. Scand. p. 234 (1861) ;
Cromb. in Journ. Bot. viii. p. 98 (1870).
Exsicc. Leight. n. 159, 189 (in B.M. set as Lecidea verruculosa);
Mudd n. 195; Larb. Lich. Hb. n. 234 (as var. cinereum) ;
Johns, n. 354.
Has been frequently confused with Lichen petrmus Wulfen as
already noted. A leading character, as described by De Candolle, is
the rhizoid-like hypotliallus which, along with the often dispersed,
mostly flat thalline areolæ, distinguishes it from the allied species!
The apothecia are usually marginate and sometimes minutely
umbonate.
Nylander (Flora Ixiv. p. 188 (1881) ) and others distinguish two
species, morphologically alike, but differing in their reaction to
potash. In one no reaction follows, in the other, Bh. eupetrmum
A. Zahlbr. a yellow colour results followed by red. The specimens
of Bh. confervoides in the British Museum give no reaction with
potash. Several forms are recorded by Leighton (Lich. FL ed. 3, p . 375)
to represent various states of the thallus : in f. albicans {Bh. petrmum
f. albicans Flot. ex Koerb. I. c.) the whitish thalline areolæ are
crowded, almost concealing the hypotballus ; in f. cinereum (Flot. I.e.),
often found on stones and flints, the fimbriate hypotballus spreads
0 2