Sorbus on Sorbus.

As we were working in the garden today Clickychick pointed out this seedling growing in the fork of the Whitebean (Sorbus aria).  It clearly isn't a this year's seedling so how we managed to miss seeing it for at least one year possibly two I have no idea.  Trees growing in the fork of other trees isn't uncommon as Kanyl showed not long ago.

The plants which grow in the tree forks are normally evolved to do this.  Many of the common Orchid species are Epiphytic (plants which grow on the surface of another plant mainly using the air and rain to supply their needs.   If detritus has gathered in a fork and decayed into humus then other plants can get a foothold there.  In this case a Rowan (Sorbus aucuparia) probably arrived as a seed in bird droppings.