FINK—THE LICHENS OF MINNESOTA. 67 
LECIDEA Ach. Meth. Lich. xxx, 32. pl. 2. f. 1, 2. 1808. 
PLATE 4. 
The thallus is crustose and variously granulose, verrucose, or areolate. Lichens 
with squamulose thalli have been admitted to the genus by many authors, but follow- 
ing our disposition of the poorly defined group Biatora, as admitted by Tuckerman, 
we have separated these. There are no definite layers of-the thallus, except possibly 
in a very few species having rather thick thalli, and even in these there is no definite 
cortex. As is usual in such rudimentary thalli, hyphal rhizoids penetrate the sub- 
stratum and serve as attaching organs. The algal symbionts are the common Cysto- 
coccus. The thallus is frequently evanescent. 
The apothecia are small, or rarely reach middle size. They are commonly adnate 
or immersed, though sessile apothecia occur in some of the species. The disk varies 
from pale to black and is flat or convex. The proper exciple and the hypothecium 
vary from pale to dark brown in sections, the former often being black macroscopically. 
The spores are simple, hyaline, and usually oblong or ellipsoid, though some species 
have spores in part 2-celled. 
The genus as above limited is closely related to Megalospora, and contains but a 
small proportion of the species placed in it by some lichenists. Psora has been ex- 
cluded because of difference in thallus structure and Biatorina, Bilimbia, Bacidia, 
and Biatorella because of diversity of spore structure. The Lecideas represent a dif- 
ferent line of evolution and are doubtless nearer the Megalosporas than are the Bilim- 
bias and Bacidias. 
Thirty-four species and subspecies have been found in the State. On trees, rocks, 
earth, old wood, and mosses. 
Type species Lecidea tigillaris Ach, loc. cit. This plant is our Acolium tigillare 
(Ach.) De Not. Thus it would seem that Lecidea must be replaced by another name 
after the lichen genera have all been typified, and the substitute will probably be 
Parmelia. 
EXPLANATION OF PLATE 4.—Fig. 1, plant. Fig. 2, apothecia and a portion of the thallus. Fig. 3, a sec- 
tion of an apothecium and part of the thallus; a, the hymenium; b, the hypothecium; c, the algal layer. 
Fig. 4, a section of the thallus; a, the pseudocortex of entangled hyphae; b, the algal layers; c, the 
medullary layer. Fig. 5, paraphyses and an ascus. Fig. 6, free spores. Fig. 7, algal cells. Fig. 1, 
natural size; fig. 2, enlarged about 10 diameters; figs. 3, 4, enlarged 425 diameters; figs. 5, 6, 7, enlarged 
650 diameters. From Schneider. 
KEY TO THE SPECIES. 
Section I. Exciple and hypothecium softish and usually light-colored (Biatora). 
Parasitic on other lichens, no thallus of its own distinguish- 
able......2....02.2 202222 eee eee eee eee eee eee eee 18. L. oxyspora. 
Not parasitic on other lichens. 
Thallus sea-green to ashy. 
Thallus areolate. 
Apothecia small or minute, disk pale flesh- 
color to black..................2.-------- 1. L. coarctata. 
Apothecia larger; disk usually black........... 2. L. brujeriana. 
Thallus granular, or if areolate tardily so. 
Thallus tardily areolate or subareolate. 
Margin of the apothecium becoming flex- 
uous; disk black and flat................ 4. L. fleruosa. 
Margin of the apothecium not flexuous. 
Disk flattish to strongly convex, pale 
brownish to black.............---- 10. L. turgidula. 
