This common condition of unknown aetiology, which affects about 10% of children and adults, is characterised by map-like red areas of atrophy of filiform tongue papillae in patterns that change even within hours.
Many zygotes were adjacent to a persistent synergid with filiform apparatus.
The filiform papillae are long and stained by accumulated debris.
Origin
Mid 18th century: from Latin filum 'thread' + -iform.