The correct option is A Lichen
Litmus, was formerly prepared only in Holland, but at present is manufactured from various lichens in Italy, France and Britain. A peculiar blue coloring matter obtained from Roccella tinctoria, Acharius, and other lichens. Roccella tinctoria, or Orchilla weed, is a small, dry lichen, with a rounded, glaucous, nearly erect thallus, forked and subdivided into numerous branchy, roundish, gray, yellowish, or brownish threads; the apothecia are scattered, red and elevated; the disks are flat, caesius, pruinose, and as broad as the border.