Thelotrema macrosporum P.M. Jørg & P. James

  Thallus crustose relatively thick containing crystals of calcium oxalate, greyish, greenish-grey, bluish-grey, often mottled whitish or cream, becoming ochraceous in old age or herbarum, hypothallus indistinct, whitish. Apothecia 0.8-1.2 mm in diameter, submerged at the top of inconspicuous hemispherical or urceolate warts with an ostiole 0.2-0.6 mm in diameter. Asci with a very variable number of spores: 1-(2)-(3)-(4)-(6), 130-170 x 40-55 µm according to the literature; 120-160 x 25-35 µm according to our measurements (at 1 or 2 spores). Spores colorless but becoming greyish when mature, roughly fusiform with rounded tips, muriform in appearance with 16-22 transverse septa and 3-8 longitudinal septa, covered with a thin gelatinous layer, (70) 90-120 (160) x (15) 25-40 (50) µm according to the literature but according to our measurements of variable size depending on their number in the asci : 125-150 x 25-30 µm for spores from 1-spored asci; 90-110 x 18-24 µm for spores from 2-spored asci; 80-90 x 16-20 µm for spores from 4-spored asci; 50-70 x 13-16 µm for spores from 6-spored asci. Thallus: C-, K-, KC-, Pd-. Rare species growing on trees with smooth bark in hyperoceanic forests, here on Ilex bark.

N.B. Thelotrema lepadinum, a much more common species in our survey area, has a whitish to cream thallus, larger, more numerous and more prominent fertile warts and smaller spores with unrounded ends.