That one's in our database as A. julibrissin 'Alba.' It was once called A. julibrissin f. alba or A. julibrissin var. alba, but both of those names are obsolete now.

Silk Tree (Albizia julibrissin 'Alba')

@zuzu , that didn't come up at all in my search for "Mimosa Tree", although seven other named varieties of Albizia julibrissin were listed. (And if I'd seen "Alba", I would've known the white variety was already noted.) I see that A. julibrissin "Alba" is only referred to as "Silk Tree", but three of the varieties that did come up in my search are also listed with the main common name "Silk Tree"; is there a way to link "Alba" to the Mimosa Tree search to help prevent future omission?

Common names are not terribly reliable due to the fact that there are no agreed-to rules governing their usage. A search of 'Albizia julibrissin' would have produced 'Alba' in it's results.

As a side note, however, I added the common name of 'Mimosa Tree' to the 'Alba' entry, which will now cause it to show up in the results if searched for by common name.

Radly, it didn't come up in your search because I just added the entry last night after reading your comment.