Why use the RHS Plant Finder?
We use the Plant Finder as an independent, comprehensive, published reference for Britain and Ireland with a 24 year record. To simplify dealing with large volumes of data in a standard way, we use the plant names as listed in it. Please direct any corrections to the Editor of the Plant Finder, but do let us know about any additional synonyms or alternative names. Other resources used on a case-by-case basis include nursery catalogues and cultivar registers.
Why does Plant Heritage’s Threatened Plants Project (TPP) include only cultivars, and not species?
Naturally occurring species are already assessed by the International Union for the Conservation of Nature (http://www.iucnredlist.org/). The IUCN Red List identifies and documents wild species’ conservation status worldwide. They do not cover man-made hybrids and cultivars.
Plant Heritage (the NCCPG, National Council for the Conservation of Plants and Gardens) exists to conserve garden plants in Britain and Ireland, and is the leading garden plant conservation charity worldwide. Cultivars uniquely represent the combination of plants’ genetic resource and horticulturists’ skill in a way that can be measured, as naming and registering individual cultivars marks them as distinct from each other.
What exactly are you listing?
We are listing correctly named cultivars only, designated in single quotes, not wild species, subspecies, hybrids or forms, nor commercial sales names or trial numbers without a cultivar name, and not groups, series or hybrids of cultivars which do not have a cultivar name themselves. Living plants of perennials, including trees and ferns, but not including seeds. We are starting with the 1,068 genera which contain at least one cultivar listed in the Plant Finder 2011-2012.
Why are we listing plants that are widely available in the RHS Plant Finder?
The initial listing includes all named cultivars which have been grown in horticulture in the British Isles. The spreadsheets to investigate rarity and identity are supplied pre-populated with names, numbers of nurseries, and many descriptive symbols. Volunteers are asked to check nursery numbers for the rarest cultivars (only 1 or 2 British nurseries per year supplying). Other information is also checked and noted, such as synonyms and year newly listed, which may be useful later to help identify cultivars which may appear threatened but actually be misnamed. These spreadsheets are used to calculate which plants are threatened in cultivation. Later, when cultivars not on the threatened list are found in other sources, this long list of information acts as a check that they are not common varieties. Lastly, plants are evaluated as threatened, not threatened or of least concern: the not-currently-threatened cultivars are recommended to be assessed again in five years’ time in case their situation has worsened.
How are conservation status and horticultural merit calculated?
Rarity, or conservation status, is calculated as a mean of the number of nurseries over the preceding five years of the Plant Finder, the Last Listed, and occurrence in Plant Heritage National Plant Collections® for which we hold a plant list within the past five years. If this value is <1 then the cultivar is said to be threatened in cultivation (THR); between 1 and 3 not threatened (NT), but worth re-evaluating in five years’ time; and >3 of least concern (LC). These categories follow IUCN designations for wild plants, although the methodology is different, and sum up rarity.
Value, or horticultural merit, is assessed by experts. Anyone with expertise on the value of cultivars in a particular genus is free to contribute.
Three categories are used: horticultural value, usefulness to people, and heritage or historical importance. A checklist has been compiled to serve as a guide to marking but there is some freedom for experts to interpret them as necessary, as different plants sometimes require different treatment. Expert assessments will be combined into final ratings of merit.
These categories are based on a 2008 survey of horticulturists, botanists and commercial nurseries by the RHS in consultation with Plant Heritage as to what they considered to be important factors contributing to horticultural merit.
Both calculations are designed to be as straightforward as possible, and broadly applicable across the full range of plants in British horticulture.
For more information, see a 2010 article by Mercy Morris and others, Prioritisation for the conservation of cultivated plants – a new approach in Sibbaldia, the Journal of Botanic Garden Horticulture, No.8, pages 111-123.
How do we find critical plants? When can we start propagating?
Cultivars can be difficult to identify accurately. Our identification of cultivars in the Threatened Plants Project relies on records kept by reputable organisations, such as botanic gardens and National Plant Collections®.
Using the TPP methodology we will know where a recorded example of the plant in question is (nursery or garden) from which source we should be able to propagate. If there are plants that may be extinct and that we would like to try and find, we will use these in campaigning by PH and our partner organisations. This is the sort of news story we are looking for!
Why are overseas nurseries not included at the listing stage?
The project only covers plants that are or have been in cultivation in the UK. Also, overseas nurseries (abbreviations starting with X) do not appear in the Plant Finder consistently, so it does not give a clear picture of whether something is genuinely available to gardeners here or not. Cultivars may be listed one year and then disappear the next if the nursery is no longer listed, giving a misleading impression. With a UK nursery, it is more likely that plants will still be in the trade, or in gardens in the UK. Experts, on the other hand, are sought from abroad as well as the UK, in order to derive a true picture of cultivars’ importance, and cultivars threatened in the UK may be able to be restocked from overseas in specific cases.
Who chooses which genera are listed?
You do! Anyone is very welcome to use the process to list any genus they consider important. In many cases, genera with few cultivars have been tried out as volunteers learn the process. Some specialists have been kind enough to take on and start listing genera with hundreds or more cultivars. Plant Heritage local groups are particularly encouraged to think about genera in their nearby National Plant Collections. The coordinator is always happy to recommend a genus which we would like done sooner rather than later, perhaps because there is already an expert available for the next stage.
Last updated 04/10/11