Niphredil

According to The Silmarillion, when Lúthien was born in Doriath '...the white flowers of niphredil came forth to greet her as stars from the earth.' (Quenta Silmarillion 10, Of the Sindar). This only really makes sense if the flowers first appeared in Doriath. Lúthien was born after the first age of the Captivity of Melkor during the Years of the Trees, about 2,900 years before the first rising of the Moon and Sun.

In a letter written in 1969, Tolkien called niphredil '...a delicate kin of a snowdrop...' (The Letters of J.R.R. Tolkien, No. 312). It's not completely clear in context how literally he meant 'kin' - that is, whether he actually meant that the two plants were related, or whether niphredil was merely a similar kind of flower in appearance. Nonetheless there was an evident connection, and the two flowers clearly had a great deal in common.

The name niphredil is explicitly translated 'snowdrop', but in The Tale of Aragorn and Arwen, we're told that after the close of the Third Age, niphredil no longer bloomed in the Mortal lands. So, if niphredil was indeed a kind of snowdrop, it cannot have been any variety that currently exists. 'Snowdrop' is actually a figurative translation of the name, which comes from Sindarin roots that translate literally as something like 'pale drop' (that is, a 'drop' in the sense of a drop of rain or snow).