The Plant Ontology Database: a community resource for plant structure and developmental stages controlled vocabulary and annotations. - Shulamit Avraham; Chih-Wei Tung; Katica Ilic; Pankaj Jaiswal; Elizabeth A. Kellogg; Susan McCouch; Anuradha Pujar; Leonore Reiser; Seung Yon Rhee; Martin M. Sachs; Mary L. Schaeffer; Lincoln Stein; et al. (Nucleic Acids Res., 2008)

Plant Structure Ontology (PSO) - A Morphological and Anatomical Ontology of Flowering Plants. - Katica Ilic; Seung Yon Rhee; Elizabeth A. Kellogg; Peter F. Stevens (Anatomy Ontologies for Bioinformatics, 2008)