Syringus seems to be derived from the Greek syrinx- that gives us the word syringe and a bunch of medical terms: http://www.wordinfo.info/words/index/info/view_unit/2075
Syrinx was also a nymph in Greek Mythology: http://www.theoi.com/Nymphe/NympheSyrinx.html
I don't see strong evidence of Syringus being used as a first name other than the archduke you mentioned, but I do see Syring as a surname and Syringa as both a surname and a first name.
This love was a bell that rang
unheard in the air.