I am looking for a general term meaning a man-made object that is given characteristics not its own. I am trying to find a broader term than anthropomorphism or zoomorphism; something including objects given plant or other inanimate characteristics. Examples of this would be plants with thimbles for flower blossoms, or a needle made to resemble a rocket.
"Ascription" would be a sensible term for your purposes; it is defined as "the action of regarding a quality as belonging to someone or something" on Google's primary dictionary (although this is the third listing in the definition of "ascription"). This is not a traditional literary term, however.
Another term that may fit your needs is "parallelism," which can sometimes refer to a certain kind of metaphor. (This term also refers to sentences that use identical grammatical patterns.) In a way, we are borrowing a grammatical term and using it figuratively. That seems appropriate for our purposes here.
In Metaphor and Art, Carl R. Hausman describes a particular line as using metaphorical parallelism in the following way.
"Thus terms such as Man, dream, and shadow, brought together in 'Man is the dream of a shadow,' manifest a certain tension as long as the prior complex of antecedent meanings for each term are attend to. This metaphor exhibits, as an expression that is an Immediate Object, a parallelism. And the something else represented in a Dynamical Object." (Hausman 227)
In this usage of the term "parallelism," the defining characteristic of the term is the presence of a comparison that directly describes one object by making reference to another and does not attempt to conflate the two things being compared as if they are identical. Rather, the comparison rests on an understanding that the "antecedent meanings" or usual conception of an object remains intact and so it described via metaphor.
In the case of your examples, this description is visual, utilizing a resemblance of shape to depict or illustrate the specific nature of one object (leaf or rocket) as being similar, but not at all identical, to another object (a thimble or a needle).
Other terms you might consider could include "metaphorical representation" or simply "comparative description"/"comparative depiction." On one level, you are discussing symbolism of a specific sort that seems to hew toward the language/terminology of visual art and which also appears in poetry. In researching the question, no perfect term seems to be available that is commonly used in literary or academic discourse.