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LICHEN ALGAE 59
Fam. TRENTEPOHLIACEAE. Filamentous and branched, the filaments
short and creeping or long and forming tufts and felts or cushions; colour,
brownish-yellow or reddish-orange.
TRENTEPOHLIA Born. Branching alternate;
cells filled with red or
orange oil ; no pyrenoids (Fig. 29). A large number of lichens are associated
with this genus : Pyrenulaceae, Arthoniaceae, Graphidaceae, Roccellaceae,
Thelotremaceae, Gyalectaceae and Coenogoniaceae, etc., in whole or in part.
Two species have been determined, T. umbrina Born., the gonidium of the
Graphidaceae, and T. aurea which is associated with the only European
Coenogonium, C. ebeneum (Fig. 3). Deckenbach 1 claimed that he had proved
by cultures that T. umbrina was a growth stage of T. aurea.
Fam. CLADOPHORACEAE. Filamentous, variously and copiously branched,
the cells rather large and multinucleate.
CLADOPHORA Klitz. Filaments branching, of one-cell rows, attached
at the base ; colour, bright or dark green ; mostly aquatic and marine
(Fig. 30). Only one lichen, Racodium rupestre, a member of the Coeno-
goniaceae, is associated with Cladophora. It is a British lichen, and is always
sterile.
Fam. MYCOIDEACEAE. Epiphytic algae consisting of thin discs which
are composed of radiating filaments.
1. MYCOIDEA Cunningh. (Cephaleuros Kunze). In Mycoidea parasitica
the filaments of the disc are partly
erect and partly decumbent, reddish
to green (Fig. 31). It forms the gonidium
of the parasitic lichen, Strigula
complanata, which was studied by
Marshall Ward in Ceylon 2 . Zahl-
bruckner gives Phyllactidium as an
alternative gonidium of Strigula- Fig. 31. Mycoidea parasitica Cunningh. much
magnified (after Marshall Ward).
CG3.C.
2. PHYCOPELTIS Millard. Disc a stratum one-cell thick, bearing seta,
adnate to the lower surface of the leaf, yellow-green in colour. Phycopeltis
(Fig. 32) has been identified as the gonidium of Strigula complanata in
New Zealand and of Mazosia (Chiodectonaceae), a leaf lichen from tropical
America.
1 Deckenbach 1893.
2 In a comparative study of leaf algae from Ceylon and Barbadoes, N. Thomas (1913) came to the
conclusion that Marshall Ward's alga in its early stages is the same as Phyllactidium ti'opicum
Moebius ; and that the Barbadoes alga with which she was working represented the older stages, it
being then subcuticular in habit, forming rhizoids, barren and sterile aerial hairs and subcuticular
zoosporangia.