Cymbalaria muralis, commonly called picardia or bell tower grass, is a species of the family Plantaginaceae,
It is a perennial, creeping grass (it grows to about 5 cm in height) growth that occurs in walls (preferably wet), rocks, walls and even sidewalks, rarely in soils.
It has round or heart-shaped leaves with three to seven lobes of 2.5 to 5 cm long and wide, located alternately on the stem. The thin stems can reach up to 70 cm in length; without pubescence. The solitary flowers, no more than 1 cm, with purple or violet corolla, arise axillary (the peduncle leaves between the leaf and the stem).
This species has an unusual propagation method. The floral stem initially has a positive phototropism, moving towards the light; after fertilization, this phototropism becomes negative (away from light), which makes it easier for the seeds to fall into the cracks in the wall or the rock where it grows in order to germinate.