I like to incorporate a bit of miniature palm when making boutonnieres. You can snip them directly off a potted plant. You need a short piece of 24 gauge wire and a small leaf from the plant.
You could tape it directly the boutonniere, but the exaggerated curve can widen the look of the lapel flower and seem like a forest of greens.
Taking a green florist wire, bend it into a wide hairpin curve that loops behind the palm branch, giving it support.
Here's a back view the the wire. This helps take out the bend of the leaf and straightens it up a bit.
It's hard to see in the photo, but I've actually looped the wire over the center branch so that it's hooked into the leaf and then taped it off at the bottom with florist tape.
Now you can see the palm has straightened quite a bit, with a flair of a curve just at the top.
Nestle the palm frond next to the rose head, opposite of the ivy leaf.
The lateral view shows that all the greens are clustered close to the rose head, creating a pleasing shape rather than an exaggerated curve had the greens not been wired.
You can see the difference between what the frond looked like before and after wiring when placed close to the rose head.