Conserving Garden Plant Diversity

Written by Yvette Harvey, Keeper of the Herbarium, Royal Horticultural Society, RHS Garden Wisley.

We live at a period in time where we are very familiar with the concept of mass extinctions that are likely to be caused by human intervention (from burning of the rain-forests, hunting and desertification through to global warming). As the years/decades/centuries progress, our preserved plant and animal [by which I mean anything that moves] collections find themselves being useful tools to provide empirical evidence for the causes of the above, outside of their main purpose of pure taxonomy (Thiers 2020: 219-242).

Following the recent closure of Kew’s Red Listing department, conservation is a subject that readily springs to mind. With c. 390 million specimens contained within the World’s herbaria, information captured in specimen labels has ultimately provided the data for calculating the Area of Occupancy and Extent of Occurrence, both of which play a large part in assessing the IUCN (International Union for Conservation of Nature) Red listing of a plant.

I am lucky to work with a specialist herbarium collection – one that contains ornamental plants based at RHS Garden Wisley. Yes, highly unlikely to play a role in an IUCN assessment, but all the same, a dried ornamental plant collection does play a vital role in conservation. Whilst Plant Heritage aims to conserve living plants, a herbarium that specialises in ornamentals (cultivars) can preserve material of long lost or even recently lost garden plants.

Brickell & Sharman wrote a seminal work on cultivated plant conservation in 1986, alas, 35 years later, the problem of lost cultivars hasn’t vanished. There are a number of reasons that ornamentals become extinct, most are human related. As gardeners, we all have our likes and dislikes; the commercial streamlining of nurseries has greatly reduced the choice of cultivars available; and introduced pests and diseases have taken their toll too. Morris et al. discuss a number of other factors in their 2010 paper. Included is loss as a result of uncontrolled hybridisation, where ‘seedlings in plant groups known to outcross routinely are distributed under the name of the cultivar, and over time the original cultivar is lost’ highlighted by the loss of the ‘true’ Dahlia ‘Bishop of Llandaff’. Similar to the IUCN Red List categories, in their paper Morris et al. set out an assessment scheme for rating cultivated plants.

I was amazed to discover that a gorgeous looking Delphinium named ‘Black Arrow’ is now likely extinct or certainly close. Introduced to great aplomb at the 2004 RHS Chelsea Flower Show, this taxon hasn’t been available for sale for a number of years and can be considered lost to horticulture. I appreciate that it may still be found in one or two gardens, but it is no longer available commercially. Fortunately a specimen was made at the time of introduction so genetic material does remain.

Delphinium ‘Black Arrow’. Sensation of the 2004 RHS Chelsea Flower Show, this cultivar is no longer available commercially. © The Royal Horticultural Society

This got me thinking about older cultivars and another Delphinium sprang to mind, and in so doing, opened another avenue – the demise of the small nursery as factor towards taxon loss. The cultivar was ‘Nymph’ and was first introduced by ‘M. Prichard & Son’ in July 1922.

Delphinium ‘Nymph’. Painted by Elsie Dykes in July 1922 from the plant introduced by Maurice Prichard. © The Royal Horticultural Society

Maurice Prichard was active as a garden designer and nurseryman in Hampshire (now Dorset), founding the Riverslea Nursery in Purewell, Christchurch in 1890 (Jecock 2021: 5-6). Now almost certainly beneath a 1970s housing estate, the nursery showed plants at RHS Chelsea and other RHS shows and Prichard bred a number of new cultivars. For the buoyant property market, this is a very sought after location – in fact, prices paid during sales of beach-huts on the adjacent Hengistbury Head frequently make the national tabloid headlines.

The RHS’s herbarium contains over 3000 non-published paintings that were commissioned as a record of awarded plants between the 1920s and 1950s. An artist was able to replicate colour far more accurately than a colour photograph at that time [colour is very important in distinguishing cultivars]. ‘Nymph’ is just one of the works painted by Elsie Dykes – and yes, it is a yellow Delphinium and almost certainly was that pale colour – difficult to believe when we are currently faced with a choice of blues and purples. In July 1931, Mrs Dykes painted another of Riverslea’s new introductions, Saxifraga ‘Riverslea’.  Regrettably both are long forgotten and not available in the horticultural trade. These images are the only way that we are able to see what they looked like.

Saxifraga ‘Riverslea’. Painted by Elsie Dykes in July 1931 from the plant exhibited by Maurice Prichard. © The Royal Horticultural Society

Morris et al. (2010: 113-115) explore the difficulty of detecting extinctions in cultivated plants. As mentioned above, long lost cultivars may lurk in glasshouses and gardens for a number of years after they have ceased being available commercially. In the recent past, one such plant, Chrysanthemum ‘Desert Song’, thought to have been lost in the 1930s, came to our attention when an RHS member requested an identification for the plant found in his recently deceased grandfather’s greenhouse. For Lachenalia ‘Monte Carlo’ David (2009) writes that we can be certain of its demise. Raised by Rev. Joseph Jacob in the 1920s, this glass-house plant appears to have been lost during WWII when glasshouses were not heated (1940 was a severe winter), or used for growing food.

Chrysanthemum ‘Desert Song’. Thought to have been extinct in cultivation for over 70 years until one of the RHS’s members sent a cutting from his grandfather’s plant to Wisley for identification.

Lachenalia ‘Monte Carlo’. Painted by Elsie Dykes in March 1926 from the plant exhibited by Messrs Carter Page & Co. © The Royal Horticultural Society

All is not gloom and doom as far as Riverslea is concerned. I am happy to report that Prichard’s legacy lives on and, in spite of some of his cultivars being over 100 years old, they are still best sellers and are listed in the latest Plant Finder as being available from a number of nurseries. You may have some of them in your garden, to name but a few: Campanula lactiflora ‘Prichard’s Variety’, Geranium × riversleaianum  ‘Russell Prichard’, Kniphofia ‘Royal Standard’ and Aconitum ‘Spark’s variety’. Although not directly from the Riverslea Nursery, specimens of these taxa in the RHS herbarium do conserve a genetic record of his cultivars.

Campanula lactiflora ‘Prichard’s Variety’. Raised by M. Prichard & Sons, Christchurch. © The Royal Horticultural Society

Geranium × riversleaianum ‘Russell Prichard’. This is the original clonal cultivar for the riversleanum type, raised at Prichard’s Nursery at Riverslea, Hampshire before 1915. © The Royal Horticultural Society

Kniphofia ‘Royal Standard’. Introduced by Maurice Prichard in 1921, this cultivar is grown internationally. © The Royal Horticultural Society

Aconitum ‘Spark’s variety’. This widely available cultivar was bred in 1898 by M. Prichard & Sons, Christchurch. © The Royal Horticultural Society

Recently moved into a larger, environmentally controlled room, the RHS’s herbarium aims to conserve the 400,000 cultivars currently grown in the UK’s gardens.

References:

Brickell, C. & Sharman, F. (1986). The Vanishing Garden – A Conservation Guide to Garden Plants. John Murray, London.

David, J.C. (2009). Lachenalia in cultivation: history and hybridisation. Amaryllids, 2009(1): 11–16.

Jecock, R. (2021).  The Immortals pt. 2: 5-6.  In Guy, D. (ed).  Hardy Times vol. 21.  Newsletter of the Hardy Plant Society, Dorset Group.

Morris, M., David, J., Upson, T. & Buffin, M. (2010).  Prioritisation for the Conservation of Cultivated Plants – A new approach.  In Sibbaldia: The Journal of Botanic Garden Horticulture 8: 111-123.

Thiers, B. (2020).  Herbarium: The Quest to Preserve & Classify the World’s Plants. Timber Press, Oregon.  Pp. 279.

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