Ceterach officinarum (Asplenium ceterach) is a fern species commonly known as Rustyback. It is characterised by a short rhizome which gives rise to several green fronds that have a pinnated lamina with trichomes on the abaxial (lower) surface, but not the adaxial (upper) one. These trichomes (hairs) are orange-brown in colour, hence the name “rustyback”. The petiole is shorter than the corpus of the leaf.This species is found in Western and Central Europe, including the Mediterranea Region. It is associated with fissures in carbonate rocks and also grows on the mortar of stone and brick walls.This fern species has been used medicinally as a diuretic.It likes growing in rocky walls, especially in alkaline ones. Can be found growing up to 2700 metres above the sea level, although it prefers mountainous locations, where it is usually found growing in sunny rocky walls.Unlike many others, this fern likes growing in full sun, and requires little, if any, humidity.