Process behind golden palm leaf
From the absence of visible leaf structure, I would guess that this is just artfully laid out gold colored tissue on canvas.  There is an inherent pun in the work because that gold tissue is usually referred to as "gold leaf".

As for making similar work from actual plant life, you might it easier to build a one-sided, open silicone mold around a plant leaf, then cast them in a mixture of clear resin and gold-colored pigment.