Thallus: Foliose, composed of broad, thin branches or lobes; the branches 0. 5-3 cm (0. 25-1. 5 in) wide and 1-2 mm (.04-. 08 in) thick. Upper surface smooth on young branches becoming powdery on old ones; pale greenish-tan when dry, becoming bright green when wet. Lower surface mottled white and tan; tan areas covered by fine yellowish hairs (use a hand lens). The thallus is attached at a central point and the branches are easily lifted from the bark.
Apothecia: (Fig. A) Sometimes present on older thalli, 1-4 mm (.04-. 15 in) across tan to chocolate brown with a thin, pale thalline margin.
Soredia: (Fig. B) Present, usually in lines of soralia following the margin of a lobe or along a fold.
Isidia: Sometimes developing in soralia of older thalli.
Comments: This large green lettuce-like lichen with its puckered thallus is easily recognized. It contains, in addition to the green algae which make its food, packets of blue-green algae which fix nitrogen in the same way that bacteria in the roots of legumes do.