I've come across two kanji, which are both read
やなぎ and both mean "willow".
From what I've found out so far,
柳 has an On'yomi of
リュウ and it seems to mean more "things with the qualities of a willow"; while
楊 has an On'yomi of
ヨウ and means the type of tree. That being said it also seems to be a name element.
Can anyone confirm this or shed some more light on the subject?