Bilberries belong to a group of similar kinds of berry that acquired their common names rather unsystematically. In Europe, the names 'bilberry' and 'blueberry' are essentially synonymous, but are entirely distinct from the North American 'blueberry' (which looks similar, but is actually unrelated). The name 'whortleberry' is also sometimes used for bilberries, but it can also refer to berries of quite different kinds. Tolkien himself used both 'bilberry' and 'whortleberry' to apparently describe distinct types of berry (his references do not go into specific detail, but Tolkien's 'whortleberry' seems to have been the red berry also called a lingonberry or cowberry, rather the dark blue bilberry).
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