Referee Assessment of Plant Genera

Since September, the refereeing process of genera with cultivars established as Critical in Cultivation by the TPP has been gaining momentum. We are reviewing and testing the assessment process as we go, and widening the feedback methods, beyond the original online format (paper copy, in person, by phone) is proving far more beneficial to our Referees and therefore improving the feedback that they are able to return to us.

In explanation of the project, the following chart lays out where the Refereeing of cultivars appears within the Threatened Plant Project (TPP) at stage 3, however it is worth adding that although the process looks at plants that are, or may be worthy of conservation, it does not mean that any should excluded. It is a means by which we can recognise and work towards protecting those currently most at risk.

Assessment methodology2


  • LCic (Least Concern in cultivation) >21 occurrences in total in NPCs, 5 years of RHS Plant Finder, Last Listed.
  • NTic (Near Threatened in cultivation) 7-21 occurrences in total in NPCs, 5 years of RHS Plant Finders, Last Listed.
  • Threatened (overall covers VUic, ENic & CRic) <7 occurrences in total in NPCs, 5 years of RHS Plant Finders, Last Listed.

Plants assessed as threatened are further sub-divided as:

  • VUic (Vulnerable in cultivation) growing at 3 or more sites
  • ENic (Endangered in cultivation) growing at 1 or 2 sites
  • CRic (Critical in cultivation) not found growing yet

A list of criteria is laid out in a spreadsheet and it is from here that the assessment process works – there is no limit to the information that we can receive for any one plant.

An example of the list as it appears when ready for Referee Assessment:

example referee list2

We have been in contact with several National Collection Holders (NCH), including holders of; Rheum, Clematis montana and C.viticella, Hydrangea and Cardamine and have received very useful and important feedback – from finding the locations of ‘lost’ cvs to those wrongly named. It is also enabling us to recognise and record that some rare cvs., although not in general circulation (eg. through Gardens Centres), are still being grown and sold in significant numbers through Plant Fairs.

Assessments for more genera are ready and being sent out for refereeing and although we had been looking initially at a specific list, we are now able to move forward and to ask for referees for a far wider set of Genera.

With the knowledge base that exists among NCHs, and where there is a NC for the Genera we want to have assessed for the TPP, we are getting in touch initially with the CHs. Through this we have been recommended further people to contact, whether through Specialist Plant Societies or nurseries and other plant collections.

CHs do for many and varied reasons have to withdraw collections, however we do recognise that the knowledge remains with the plantsmen and women involved and therefore (where appropriate) we have also asked and are receiving wonderful help from former Collection Holders. Also, if you have knowledge of specific genera, even if you are not a NCH, we would love to hear from you.

Thank you to everyone who has helped or is helping us so far, your knowledge is valuable – and we still have a very long way to go. If you haven’t heard from us (yet), but would like to be involved with this aspect of the project, do let us know.