Least Water-lily, Nuphar pumila - conservation by Royal Botanic Gardens, Kew

Today is the 20th Anniversary of the establishment of the Millenium Seedbank, located in Sussex.  It is the world’s largest underground seed bank & conservation resource for global wild plant species.  For more info on the project check out the MSB webpage.

It seems a fitting day to provide an update of the project which started in 2016 to review the genetic status, ecology, and condition of Least Water-lily Nuphar pumila, at Cole Mere, Shropshire, the only population in England. 

Nuphar pumila Least Water-lily, by Dan Wrench

The partnership included SBS, Natural England, the Royal Botanic Gardens (RBG) UK Native Seed Hub, Conservation Genetics and nursery teams, Richard Lansdown (Chair IUCN Freshwater Plant Specialist Group), site managers Shropshire Council, and also volunteers from the Shropshire Wildlife Trust and Colemere Sailing Club.  The latter provided boat transport for a local Dive Club who were enlisted to count the number of petioles emerging from the rhizomes, not their usual dive remit but it was received enthusiastically after a little training.

The vulnerability of the species at Cole Mere was of concern and the project aimed to:

1. Provide a summary of the ecology of Nuphar pumila, management and monitoring recommendations

2. Carry out seed viability tests, and propagate seeds and rhizomes for ex-situ conservation and public display at Kew

3. Carry out DNA analysis to detect hybridisation with Yellow Water-lily Nuphar lutea, also present at Cole Mere.

4. Devise an in-situ conservation management plan.

Seed pods were carefully collected, making sure they were the right species.  The seed pod has a lobed stigmatic disk in contrast to Yellow Water-lily Nuphar lutea which is also present at Cole Mere.

Nuphar pumila with lobed stigmatic disk

The Nuphar pumila seeds were found to be 95% viable, which was great news.  BUT successful germination depended on very specific conditions, especially light levels and only 10 live seedlings  were obtained from 100’s of seed, which was very labour intensive.  Even worse news, all of these seedlings subsequently died.  The seedlings were watered with tap water and Kew had problems with algal growth.

So hopes are now pinned on the rhizomes which were collected during the same operation.  Each year many free floating rhizomes are found on the lake edges, possible uprooted by waterfowl, likely mute swans feeding on the submerged leaves.  Some of the less bruised ones were collected and taken for propogation, but the majority were too battered and died:

Nuphar pumila rhizomes pulled up by waterfowl

However, recent news from Kew is that from the remaining rhizomes with healthy shoots they have managed to divide these and have several healthy plants in the collection which they hope to divide again.  The best conditions appear to be a loam based compost and outside in ambient conditions rather than indoors in a controlled environment.  The mixed success of the propogation shows how important it is to ensure in-situ conservation measures at Cole Mere are as favourable as possible for the species and to continue to monitor the populations.