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New Plant Ontology Release #20 Available

Greetings from the Plant Ontology!

We are pleased to announce that the latest release of the Plant Ontology, version #20, is available on our browser at For full details of the changes, please see: the Release 20 page at:

Release features:

  • Addition of 48 new terms, for both the Plant Anatomical Entity (44) and Plant Structure Development Stage (4) branches.
  • Major revisions to the plant anatomical entity branch of the ontology include:
    • New terms were added to describe the parts of the perianth (PO:0009058), specifically to describe the different forms of a fused perianth (PO:0025880), such as that found in [ Musa flowers].
    • Thirteen new terms were added to describe the different types of protoxylem (PO:0000272) tissue in the roots and shoots of vascular plants.
    • A term was created for plant sap (PO:0025538) and six sub-classes were added to specify from which part of the plant the sap was collected.
    • We revised the existing tapetum cell (PO:0025543) (was 'tapetal cell') and added three child terms to specify the different types. In collaboration with the Gene Ontology, the corresponding GO biological process terms (anther wall tapetum cell differentiation; GO:0048657 and anther wall tapetum cell fate specification; GO:0010234) were also revised to match.
    • Inflorescence branch (PO:0009081) and its child terms were extensively revised. The existing term paraclade (PO:0004720) was merged into primary inflorescence branch (PO:0006321) and three new child terms were created the describe different types of paraclades: accessory paraclade (PO:0025546); cauline paraclade (PO:0025547); rosette paraclade (PO:0025548).
    • All the children of inflorescence branch (PO:0009081) and infructescence branch (PO:0025243) designating the different branching orders (primary, secondary etc) were renamed from xxx axis to xxx branch.
    • trichome (PO:0000282) terms: Two new direct children of plant structure (PO:0009011) were added to describe the apical regions of different types of trichome (PO:0000282): trichome apex (PO:0025550) and trichome tip (PO:0025549). They have this unusual parentage since they can be part of a multicellular trichome (PO:0000282), making them a 'portion of plant tissue (PO:0009007)', or part of a unicellular trichome (new PO:0025537), in which case they are a GO cellular component: unicellular trichome apex (GO:0090552) or unicellular trichome tip (GO:0090553).
    • We also added the subclasses: multicellular trichome apex (PO:0025551) and multicellular trichome tip (PO:0025535) and a new term was added to describe a unicellular trichome (PO:0025537).
  • Major revisions to the Plant Structure Development Stage branch include:
    • Flower development stage (PO:0007615) and its sub-classes. The five existing sub-classes which were revised into a new set of three classes and sub-classes which better describe flower development across flowering plants.
    • A new term flower meristem transition stage (PO:0025588) was added to describe the transition of the meristem from a vegetative to reproductive state.
    • The second stage floral organ formation stage (PO:0025585), encompasses three sub-classes (formerly direct children of 'flower development stage (PO:0007615)') and ends with the onset of the flowering stage (PO:0025586).
    • The new third stage is the flowering stage (PO:0007616) (formerly ''4 anthesis stage''). The flowering stage begins when pollen is released by anther dehiscence (GO:0009901) and/or the stigma (PO:0009073) is receptive and ends with the process of pollination (GO:0009856), and/or floral organ senescence (GO:0080187). This term also encompasses 5 post anthesis stage (PO:0007617) which was merged into it.
    • A new relation "preceded_by" was added to the Plant Ontology in order to order the plant structure development stages. You can find more details about the new 'preceded_by' relation here:
  • In addition to these changes, the names and definitions of many other terms have been revised.
  • New and updated annotation data for: