FINK—THE LICHENS OF MINNESOTA. 211 
Family TELOSCHISTACEAE. 
This family consists of the two genera, Placodium and Teloschistes, though some 
lichenists have made more genera by further subdivision. The peculiarities of the 
family are the yellow or orange color, due to a deposit of chrysophanic acid com- 
monly found in both thallus and apothecia, and the typically polar 2-celled spores, 
found constantly or sometimes in nearly all of the species of the two genera. 
Of the two genera, Placodium with its commonly crustose thallus is plainly the 
lower, and the spore resemblance in the two would seem to indicate that members of 
the genus Teloschistes were derived phylogenetically from some species of Placodium. 
Also the algal symbiont Cystococcus is common to both genera. 
Squamulose, foliose, and fruticose thalli occur in the family, and the apothecia 
are either adnate or sessile. The spores may rarely be nonpolar or even simple. 
The relationship between the family and the Parmeliaceae was stated in the descrip- 
tion of that family and need not be given here. In form and anatomy of the thallus, 
and in spores and apothecial characters, there is also a less close relationship between 
the present family and the Physciaceae, the nearest approach of the two families 
being in the genera Teloschistes and Physcia, Placodium and Rinodina being some- 
what less closely related as to thallus structure, but equally close as regards the spores. 
PLACODIUM (Ilill) Web. in Wig. Prim. Fl. Hols. 90. 1780. 
The thallus varies from subfoliose to strictly crustose forms, the latter being much 
more common. As in Lecanora, the thallus is closely adnate even in the best devel- 
oped or subfoliose forms. In these the upper cortex is fairly well developed and 
commonly shows more or less of cellular structure, while the lower cortex is much 
thinner and more commonly composed of closely interwoven hyphe. Even in the 
more crustose species an upper cellular cortex is often more or less developed, and 
on the whole these crustose thalli are better developed than the similar ones of the 
Lecanoras. Algal and medullary layers are also frequently demonstrable in sections, 
especially in the more foliose forms. Rhizoids or rhizoidal hyphe are present as 
attaching organs, but are by no means common and are not often noticed in sections. 
The algal symbiont is Cystococcus. The common colors of the thallus are yellow 
and orange. Fruticose forms are admitted to the genus by some lichenists. 
The apothecia are commonly rather small and sessile or adnate. The exciple is 
commonly thalloid, though a proper exciple is frequently more or less distinctly 
developed within this. Also the thalloid exciple may disappear, leaving the struc- 
ture strictly biatoroid. Orange, yellow, and brown are common colors of the disk. 
The hymenium, hypothecium, and asci are much as in Lecanora. The paraphyses 
are also similar, but scarcely so slender, The spores are hyaline and usually of the 
polar 2-celled type, but in some of the species they are simply 2-celled and partly 
simple. 
The more crustose and less lobed forms are sometimes separated as the genus Cal- 
lopisma, but the transition is a gradual one, and it has seemed best not to divide the 
species. The transition in spore forms is also gradual, polar and nonpolar or 2-celled 
and simple spores quite commonly occurring in the same species and even in the 
same apothecium. As to spore characters, the present genus is plainly related to 
Teloschistes. As to thallus structure, the relation is as plainly with Lecanora, the 
structure being as a whole rather higher in the present genus. 
Fifteen species and subspecies occur in the State. On trees, rocks, and old wood. 
Type species Placodium candelarium (L.) Web. loc. cit. 
