Schaereria serenior is a species of saxicolous (bark-dwelling), crustose lichen in the family Schaereriaceae. Found in Finland, it was first formally described as a new species by the Finnish lichenologist Edvard August Vainio, who classified it as a variety of the species Lecidea tenebrosa. Auguste-Marie Hue promoted it to distinct species status in 1913 as Lecidea serenior. Alexander Zahlbruckner proposed to transfer it to the genus Caloplaca in 1931. Most recently, Orvo Vitikainen transferred it to Schaereria in 2004, a few years after that genus had been resurrected from a long period of disuse. It is one of two species of Schaereria found in Finland; the other is S. parasemella.