Are there ontologies for the description of the look of plants?
To transform an object in an ontology to an image of that object?  Sounds unlikely, I doubt that any botanical ontology is that developed and detailed.  It would be great if it worked.  Could be used to check the ontology.  The website https://www.ebi.ac.uk/ols/ontologies lists 251 biological ontologies.  There are several on specific plants or groups of plants (brassica, beet, oats) and several that might be more relevant to you: Plant Ontology, Plant Phenology Ontology, and Plant Trait Ontology,