Julius Caesar and, through him, his adopted son, the Emperor Augustus claimed descent from Iulus or Julus, the founding ancestor of the Julian clan. One of Virgil’s purposes in composing the Aeneid was to exalt his patron’s ancestry by showing how Iulus was descended from Aeneas and thus ultimately from the goddess Venus. Thus Virgil relates that Aeneas’ son Ascanius became known as Iulus in Italy and that the the two are in fact the same person.
Other commentators have told the story differently; Dionysius of Halicarnassus related that Iulus was a son of Ascanius, while Livy made him a son of Aeneas and his Latin wife Lavinia, and thus half-brother to Ascanius. The existence of different versions of the story seems to suggest both that the connections was generally accepted and that the details were obscure. Virgil’s suggestion of a name change, however, struck me as the least convincing possibility – at least, until I considered the possible meanings of the names.
Ascanius and Iulus are generally considered to be Greek names and are interpreted as deriving from that language – despite the fact that Aeneas and his family were believed to be Trojans. Ascanius is said to mean ‘tentless’ and to refer to the flight from Troy when he didn’t even have a tent to shelter in. Obviously, for this etymology to work, he would have had to adopt this name after leaving Troy. Iulus is said to mean ‘downy’ from the Greek ioulos and to refer specifically to the ‘downy beard of a youth’.
However, iulus, is also used to mean ‘down’ in Latin, though there it is specifically used of down of plant origin, such as thistledown. Now there are several words used for different types of thistle in Latin. but one of them is ‘acanus’.
Could it be that early Latins, meeting an individual with a name like Ascanius interpreted it as ‘thistle’? And then perhaps have nicknamed him, or a younger relative, ‘thistledown’?