'A shrub' or 'plant,' as in Genesis 21:15, denotes perception, but so little that it is hardly anything, in same way as 'trees,' but to a lesser degree. So 'to be cast under one of the shrubs,' signifies being destroyed regarding truth and good, to the point of desperation.

(References: Arcana Coelestia 2682 [1-3])

Cities of the mountain and cities of the plain (Jeremiah 33:13) signify doctrines of charity and faith.

(References: Arcana Coelestia 2418)