In

in (preposition) – location reference, e. g., (1) in parathecium, amphithecium or amphithecial cortex, (2) in soralia or soredia, (3) in subhymenium, (4) in thallus upper or lower medulla, (5) in the inner or outer layer of the central axis, (6) in upper or lower thallus cortex, @@@@@@

See also: "in (taxonomic)"