LP+flagrant

Flagrant : shockingly noticeable or evident; obvious; glaring  "Under the summer roses, when the flagrant crimson lurks in the dusk of the wild red leaves, love, with little hands, comes and touches you with a thousand memories, and asks you beautiful, unanswerable questions."

The stanza this word is used in is about love. Red signifies love or passion. I think the author used this word to emphasize exactly how bright and unmistakable these wild red roses are.