Sticta beauvoisii
Sticta fuliginosa
Sticta limbata
Sticta "weigelii" (a misidentification for North America, but I've retained the name for now as a place holder)

Stictis urceolatum

Strangospora moriformis

Strigula stigmatella
Strigula (unidentified species)

Sulcaria badia
Sulcaria spiralifera

Synalissa ramulosa
Synalissa symphorea (see Synalissa ramulosa)

Teloschistes chrysophthalmus
Teloschistes exilis (photos are probably the fertile form of T. flavicans)
Teloschistes flavicans

Tephromela atra

Tetramelas papillatus

Texosporium sancti-jacobi

Thamnolia subuliformis
Thamnolia vermicularis ("apparent misidentification for North America", but I've retained the name for now as a place holder)

Thecaria quassiaecola

Thelidium pyrenophorum

Thelomma californicum
Thelomma mammosum
Thelomma occidentale (see Pseudothelomma occidentale)
Thelomma ocellatum (see Pseudothelomma ocellatum)
Thelomma santessonii
Thelomma (unidentified species)

Thelotrema lepadinum
Thelotrema subtile

Tholurna dissimilis

Thrombium epigaeum

Thyrea confusa
Thyrea (unidentified species)

Tingiopsidium elaeinum
Tingiopsidium isidiatum
Tingiopsidium sonomense

Toninia alutacea
Toninia arctica
Toninia candida
Toninia ruginosa
Toninia sedifolia
Toninia squalida
Toninia subdispersa?
Toninia tristis subsp. asiae-centralis
Toninia (unidentified species)

Trapelia glebulosa
Trapelia placodioides
Trapelia stipitata

Trapeliopsis californica (see Trapeliopsis glaucopholis)
Trapeliopsis flexuosa
Trapeliopsis glaucopholis
Trapeliopsis granulosa
Trapeliopsis pseudogranulosa
Trapeliopsis steppica
Trapeliopsis walrothii (see Trapeliopsis glaucopholis)

Tremolecia atrata

Trypethelium aeneum (see Astrothelium aeneum)
Trypethelium subeluteriae
Trypethelium tropicum (see Nigrovothelium tropicum)
Trypethelium variolosum (see Astrothelium variolosum)
Trypethelium virens (see Viridothelium virens)

Tuckermanella coralligera
Tuckermanella fendleri

Tuckermannopsis americana
Tuckermannopsis chlorophylla
Tuckermannopsis ciliaris
Tuckermannopsis orbata
Tuckermannopsis platyphylla
Tuckermannopsis sepincola
Tuckermannopsis subalpina
Tuckermannopsis (unidentified species)

Umbilicaria americana
Umbilicaria angulata
Umbilicaria caroliniana (see Lasallia caroliniana)
Umbilicaria cinereorufescens
Umbilicaria cylindrica
Umbilicaria decussata
Umbilicaria deusta
Umbilicaria hyperborea
Umbilicaria krascheninnikovii (see Umbilicaria polaris)
Umbilicaria lyngei
Umbilicaria mammulata
Umbilicaria muehlenbergii
Umbilicaria phaea
Umbilicaria polaris
Umbilicaria polyphylla
Umbilicaria proboscidea
Umbilicaria rigida
Umbilicaria torrefacta
Umbilicaria virginis
Umbilicaria (unidentified species)