From Darwin to Rackham, via primroses and climate change
This week’s post is a bit of a ramble, but stick with me, there is a logic to this. I hope you find it interesting as I discuss the floral structure of primroses and the advancing spring
My ramble starts on Monday 12 February when Thought for the Day on Radio 4 Today was by Rev Dr Livingstone Thompson who talked about Charles Darwin, evolution and his legacy, it being Darwin’s birthday (12/02/1809) which got me thinking about his work.
Primroses
One of the very early spring flowers in bloom in the garden at the moment is the primrose (Primula vulgaris) and it was it’s floral structure that caught Darwin’s eye. He noticed that there were two types of flower. One had a long style and low anthers with small pollen, which he called pin-headed, and the other had a short style, high anthers and large pollen that he called thrum-eyed. Darwin worked out that this arrangement meant that the plants were self incompatible, so ensuring cross pollination which would maintain genetic variation and contribute to natural selection.
It’s easy to check. Look down into the flower’s throat – if you see the yellow ball of the stigma, it’s a pinheaded flower. If you see a darker ring of anthers, it’s a thrum. This arrangement is found in other related species of primula – the cowslip (P. veris) and the oxlip (P. elatior) The oxlip looks very similar to the cowslip, but with pale yellow flowers that lie all to one side so its lop sided. There are also hybrid called the false oxlip that is a cross between primroses and cowslips, but the flowers are not one sided The oxlip is found in East Anglia and can be associated with ancient woodland.
In fact, the pin and thrum observation was first recorded by John Stevens Henslow, Darwin’s botany teacher at Cambridge and they exchanged numerous letters over the observation. Henslow had a vital role in the history of the herbarium at Cambridge as he remounted more than 3,000 of the original 18th century specimens in the collection and added the same number again of his own. Henshaw was also responsible for mounting and labeling Darwin’s specimens, including the 1400-odd specimens he collected on The Beagle.
Tracking climate change
Specimens stored in the world’s herbaria are important for tracking climate changes, as the mounted samples have other records, such as the time and place of collection. The records in the Cambridge University Herbarium, together with more recent observations have been used by a team at Cambridge University, led by Professor Ulf Buntgen, to put together data on the advancing spring. More than 80 observations of Primula vulgaris were included. I have mentioned this study before (https://www.cam.ac.uk/research/news/uk-plants-flowering-a-month-earlier-due-to-climate-change). They found that the first flowering date of short-lived, low growing herbaceous perennials has advanced by almost a month since the mid-1980s, compared with all the observations of the preceding years since 1753 and spring continues to advance by five days a decade.
So its not surprising that we are seeing primroses in flower much earlier. The clump of primrose in flower in my garden is particularly early for my garden, appearing at the start of the month and it’s well ahead of the others. This may be the result of it being sheltered by a south-facing wall.
Essential for spring insects
Primroses are rich in nectar and are visited by a wide variety of bees, butterflies and moths (bumble, hairy footed flower bee, bee-fly, brimstone, silver ground carpet moth, board bordered yellow underwing to name a few). It is also a primary larval food plant for one of the UK’s rarest butterflies, the Duke of Burgundy (Hamearis lucina). In fact, more than 40 species of invertebrates have been recorded as relying on it as their larval food, so it’s worrying that the primrose is flowering earlier and earlier as it could have a knock on effect on those species so dependent on it.
Do you love those brightly coloured primroses?
The garden centres are full of colourful primroses for your spring flower displays. Plant breeders have produced a huge array of FI hybrids that have a more uniform season of flowering and produce more flowers in a wider range of colours, but just how resilient are they? One research project (Lewis et al) set out to answer this question, by looking at the resilience of Primula hybrids to waterlogging and drought compared with the parent species. The researchers recreated conditions, such as a wet winter followed by dry spring and summer, and found that, in most cases, the ‘wild’ primrose with pale yellow flowers was more tolerant of the fluctuating conditions and was able to bounce back, while the cultivars suffered from a loss of quality.
The researchers also compare the three Primula species. The primrose has a wider ecological niche than the cowslip or oxlip, and this may mean the common primrose is better placed to tolerate changing conditions, more able to cope with periods of waterlogging and drought, while the oxlip didn’t cope so well with a dry spring and summer, something that correlates to its distribution. The researchers conclude that even in a garden situation, species with a narrower ecological niche may struggle if conditions continue to diverge from those that they are adapted to and, in time, climate change may reduce the range of cultivated plants we can grow in in our gardens, so gardeners planning for more climate resilience should consider wild species or less highly bred genotypes, than the more flamboyant highly cultivated cultivars we see on sale today.
The oxlips of Hayley Wood
The oxlip is one of the iconic plants found growing in Hayley Wood, a fabulous ancient wood lying to the west of Cambridge. I spent many a day there, sometimes studying, other times with the conservation volunteers, coppicing the woodland on a traditional rotation and, at other times, helping the deer counts at dawn.
Hayley Wood is a much studied woodland reserve, but one of the key books was Hayley Wood: Its History and Ecology with the beautiful drawing of an oxlip on the cover. The author was Oliver Rackham.
And it was by chance that when scrolling my Instagram feed on Monday morning, that I read Jo Thompson’s (@jothompsongarden) post about Corpus Christi celebrating 40 years of women at the college. She mentioned Oliver Rackham, who was one of the fellows of the college, saying “I was there during the time of Fellow Oliver Rackham and remember always being amazed and intrigued by the historical ecologist. I was in awe of his huge knowledge and understanding of the landscape. He was fascinating and inspirational, the way he had dedicated his life to something that I had taken for granted up until then was really something enlightening to me. Little did I know that 35 years later I’d be reaching regularly for his books which sit on my desk.”
As a botany student at Cambridge, I was so lucky to have been taught by Oliver. During the long vacation, the botany group was taken on a tour of the key habitats in SE England, including beechwoods in the Chilterns, chalk grassland of the North Downs , fenland and breckland. It was such an immersion in ecology. I will never forget Oliver taking us around the beechwoods, explaining the role of beech in history and furniture making, as well as getting us to lie down and look up through the canopy to observe the way the leaves of individual trees were arranged. I suspect that if I dig through my field notes, I will find the results of ecological surveys we did at the time, and how interesting it would be to revisit and compare.
Sadly, the beechwoods are threatened by climate change. The beech may like the thin, chalky soils and warmer climate of the SE, but as the temperatures warm up, even the beech is thought to be at risk.
And to complete the cycle of coincidences – Jo Thompson (substack The Gardening Mind) is speaking at the NW Pacific Garden and Flower Festival in Seattle and Kim is chairing the session. We look forward to hearing about it!
New books coming ….
Both Kim and I have new books coming out in the coming weeks. The American edition of Kim’s book The Climate Change Resilient Vegetable Garden comes out this week while she is in Seattle, and publishes later this month in the UK. My latest book, The Resilient Garden and Allotment Handbook publishes on the 21 March. Despite their similar sounding titles, their content is very different!