How about couching or a decorative stitch?

If it is a piece that small I would forget applique and just use a satin stitch to replicate the piece (ie: a stem perhaps?)

I've attached that small a piece to applique -- I've also used invisible thread -- but my fear is safety, particularly if it's a baby quilt. Anything that I attach to a baby quilt MUST be fully attached -- sewn down. A baby could choke on something that comes loose and I won't risk that with something I'm making! Every piece is sewn securely and I tie knots on the back side of each appliqued block for every stitch I use to applique. I won't risk not sewing the pieces down!

I think these tiny pieces need to be fastened down securely or they will come loose and/off. I use a few hand stitches to hold them down because the sewing machine can chew up those tiny pieces. No one will ever know!.