Abstract
The ultrastructure of 13 crustose lichens from Louisiana was studied to identify the genera of the trentepohliaceous phycobionts. On the basis of crosswall configuration, Trentepohlia was confirmed as the phycobiont in species of Arthonia, Anisomeridium, Pyrenula, and Trypethelium. Phycopeltis was confirmed to be present in species of Mazosia, Opegrapha, and Porina, as well as in three (Graphis, Schismatomma, and possibly a second species of Anisomeridium) in which Trentepohlia had previously been reported by others. A third trentepohliaceous genus, Cephaleuros, was found in Strigula complanata, a foliicolous lichen. Haustoria were found in all lichen species studied. The algal cell wall invaginates ahead of the invading haustorium to some extent in all, corresponding to Honegger's intraparietal condition of haustorium. In several, however, the algal wall appears to undergo thinning or disintegration around the tip of the haustorium. This progressive loss of algal wall can result in a condition similar to the "intracellular" condition of Honegger.
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