Protoblastenia incrustans General description: Thallus immersed, inconspicuous, whitish to grey or yellowish. Apothecia 0.2-0.5 mm diam., in pits, the disc flat becoming slightly convex, yellow-orange; hypothecium colourless to yellowish. Ascospores 9-13 × 4.5-6 µm, ellipsoidal. On hard limestones. Throughout Britain and Ireland (rare in E. England). Distinguished from Protoblastenia calva and P. rupestris by the small, often pale orange apothecia, immersed in pits in the rock. Description adapted from Lambley & Orange (2009). Map © BLS.