I have made many of the flowers, I love them!
I have made pedals out of tons of different woods. maple, yellow heart, cedar, poplar, walnut, bloodwood, purpleheart.
The middle button I use a different wood, but any of the same ones as the pedals.
For the stem I have used poplar, cedar, hickory and maple. I also used a dowel that had warped some how, but I don't know if I could ever bend one to make it work. My selection of the stem material is usually based on what piece of wood I have that will fit the stem. My wood stash isn't always well stocked in long pieces with the grain in the right direction.
Some of the stems are a little weak, but it is an easy part to make and replace so try something!
Also use hot-glue to stick the pedals to the middle button. It is so much easier then perfectly sanding every piece flat on the tip.
MrsN