When Celia tries to cheer up her beloved cousin Rosalind (who has just been booted out of court), she calls her "my sweet Rose,/ My dear Rose" (1.2.3). In case you hadn't noticed, it's pretty easy to shave "Rosalind" down to "Ros," which, if you buy a vowel, brings you to "rose." This makes us think of another Shakespeare play, Romeo and Juliet. (Recall Juliet's famous balcony speech, "What's in a name? That which we call a rose, by any other word would smell as sweet." Also, before Romeo fell for Juliet, he was crushing on a girl named...Rosaline.) Roses seem to have had particular significance to Shakespeare.
In As You Like It, Shakespeare has some fun with the Rosalind/Rose pun. When Touchstone makes fun of Orlando's sappy love poetry, he sings "He that sweetest rose will find/ Must find love's prick and Rosalind" (3.2.13). Translation: Love can be pretty sweet, like a rose, but it can sting too, especially if a girl's got a "thorny" personality. (Yep, Touchstone is totally bagging on Rosalind.) Touchstone is also punning on the word "prick," which even in Shakespeare's day meant 1) thorn and 2) penis. In other words, Touchstone calls attention to the fact that Rosalind is disguised as a young boy, "Ganymede," and is pretending to have a "prick" of her own.