Two varieties are of interest here: the common whitebeam (Sorbus aria), and Swedish whitebeam (S. intermedia = S. suecica). They bear distinctive white flowers and their leaves are generally lighter than other deciduous trees such as beech, birch, oak. The underside of the whitebeam is particularly light in colour and distinctive. They are thought to have been used as markers or borders of territory, their leaves' light colouring being clear at a distance. -
Cf. Haw
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.