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New Plant Ontology Release #20 Available

We are pleased to announce that the latest release of the Plant Ontology, version #20, is available on our browser at

This full release features the addition of 48 new terms, for both the Plant Anatomical Entity (44) and Plant Structure Development Stage (4) branches.

This Release also includes new and updated annotation data for: rice (Oryza sativa) Arabidopsis thaliana and cotton (Gossypium hirsutum).

Major revisions to the plant anatomical entity branch of the ontology include new and revised terms and definitions to describe:
- parts of fused perianth (PO:0025880), such as that found in [ Musa flowers]
- different types of protoxylem (PO:0000272) tissue in the roots and shoots of vascular plants
- plant sap (PO:0025538) and sub-classes
- tapetum cell (PO:0025543) and sub-classes
- inflorescence branch (PO:0009081) and sub-classes; accessory paraclade (PO:0025546); cauline paraclade (PO:0025547); rosette paraclade (PO:0025548)
- infructescence branch (PO:0025243) and sub-classes
- sub-classes and parts of trichome (PO:0000282): trichome apex (PO:0025550) and trichome tip (PO:0025549) were added to describe the apical regions of different types of trichome (PO:0000282). Also, multicellular trichome apex (PO:0025551) and multicellular trichome tip (PO:0025535) and a unicellular trichome (PO:0025537) were also added.

Major revisions to the Plant Structure Development Stage branch include changes made to 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.
- flower meristem transition stage (PO:0025588) was added to describe the transition of the meristem from a vegetative to reproductive state.
- floral organ formation stage (PO:0025585), encompasses three sub-classes (formerly direct children of 'flower development stage') and ends with the onset of the flowering stage.
- flowering stage (PO:0007616) (formerly ''4 anthesis stage''). This term encompasses the former ''4 anthesis stage'' and "5 post anthesis stage" terms

- 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.
For full details of the changes, please see: the Release 20 page at: