I learned this carol while singing in the Men's Chorus at Golden Gate Baptist Seminary around 1979. I am amazed sometimes that it takes me so long to learn about some of these treasures. We sang it acapella during that Christmas season, and it became one of my favorites.
Originally known as "Es ist ein Ros entsprungen," this German Marian hymn dates back to the 16th century. The English translation "Lo, How a Rose E'er Blooming" was written by Theodore Baker in 1894.