This is a tutorial for a basic leaf which is useful for knitted flowers and applique. The yarn and needles suggested are merely options for this pattern, and you can really use almost any yarn or knittable wire you like, with approprately sized needles. Have a play with it! These can be used as the petals to a flower too.

The blog post also includes a YouTube tutorial.

If knitting in wire, I would suggest 36 gauge beading wire held double.