Our recent goal for the Plant Ontology (PO) is to have it integrated with the Gene Ontology (GO). The simplest aspect of this is to link morphological and anatomical images of structures for PO terms with genes involved in the development of those structures (GO terms). This, also, would include images of expression analyses by in situ hybridization. By using a process of reciprocal illumination, we will be able to clarify and/or redefine PO terms. In particular, an example of this is the integument development during ovule maturation in seed plants. Gymnosperms have one integument; whereas, Angiosperms (flowering plants) have two integuments, i.e., an inner integument surrounded by an outer integument. The question that arises is which of the two integuments in the Angiosperms is the equivalent of the single integument in the gymnosperms? In Angiosperms, the gene INNER NO OUTER (INO) is involved in the proper development of the outer integument but not in the inner integument and in ino mutants there is no outer integument. INO genes are angiosperm specific as no orthologs have been found in gymnosperms. Thus, it appears that the inner integument of the Angiosperms is equivalent –homologous- to the single integument of the gymnosperms and the PO terms can be revised accordingly. Keywords: Angiosperm, Gene ontology, Gymnosperm, Integument, Ontology, Ovule, Plant ontology