I have heard of various ways of interpreting that recipe, ranging from using the aloe vera root, the dried leaves, and even aloeswood, which is a totally different plant (a tree, actually). Since the recipe states "aloe," it makes sense to use whichever part of the aloe plant you can acquire. The more important part is to perform the blessings and prayers so that the elemental is brought to work. The plant material is just the "reference" for the elemental.