Sunday, 30 August 2020

Wildflower of the Month: August: Autumn Lady's-tresses

Autumn Lady's-tresses
Image: J. Dunn
Since March, BSBI Head of Science Kevin Walker has been focusing on a different wildflower each month and telling us a bit more its distribution, its ecology and crucially, why it's important to him as a plant enthusiast as well as a scientist. As the summer draws to a close, Kevin turns his attention to Autumn Lady's-tresses:  

"For many botanists, seeing Autumn Lady’s-tresses Spiranthes spiralis is a bittersweet moment as it is the last of our 52 orchids to flower each year, as so memorably recounted by Leif Bersweden (2017) in The Orchid Hunter. What Leif doesn’t tell us is that it can also be a very painful experience as its downland haunts are often infested with Harvest Mites Neotrombicula autumnalis which, as their name suggests, peak at this time of year.

We are blessed with four of these diminutive orchids in Britain and Ireland. All four are discussed in Jon Dunn's excellent Orchid Summer (2018) although sadly, the most regal, Summer Lady’s-tresses S. aestivalis, is no longer with us having been last seen in the New Forest in 1952: zoom in to this BSBI distribution map to see those long-ago records in just one grid square. It’s North American cousin Irish Lady’s-tresses S. romanzoffiana is scattered in the Hebrides and Ireland, although your chances of seeing them are slim as its appearance is somewhat erratic. [LM: Going out with fellow botanists on a BSBI field meeting, once Covid restrictions are lifted, will increase your chances of seeing rare plants like Irish Lady's-tresses!] 

Autumn Lady's-tresses (detail)
Image: J. Dunn
Creeping Lady's-tresses Goodyera repens is more straightforward. Head to a known site in the pinewoods of northern and eastern Scotland and, by virtue of its clonal habitat, you’re more than likely to find it. If that’s too far to travel then there are a few good sites in northern England and north Norfolk where some say it was originally introduced with conifers. 

In contrast, tracking down an Autumn Lady's-tresses should be a doddle: it is relatively common in coastal regions of southern Britain and Ireland with populations extending as far north as Sligo, the Lake District and the North Yorkshire Moors. Although it has a predilection for coasts there are plenty of inland populations – possibly the most landlocked is on an industrial estate in Banbury where it was first discovered in 2018.

All four lady’s-tresses have a spiral of creamy white flowers resembling a braid of plaited hair, hence the name. These plaits are well developed in Autumn Lady’s-tresses with a dozen or so twisting up the bluish stem. The tubular flowers open sequentially from the bottom in a way that ensures that older flowers are always pollinated by younger flowers from a different plant. Self-fertilisation is not an option and so it relies entirely on bumblebees for pollination. The mechanism seems a good one as seed production is invariably very high. The sequence of images below by Jon Dunn shows a bumblebee in action - click on the image to enlarge it. 


In common with a number of other British orchids, the leaves of Autumn Lady's-tresses disappear during the height of summer but a new rosette appears in the autumn, persisting throughout the winter and spring. Indeed, winter is one of the best times to search for Autumn Lady’s-tresses as the ‘plantain-like’ rosette of glossy, green leaves are easy to spot amongst the dead grasses.

Autumn Lady's-tresses on the grassland
above Morecambe Bay
Image: R. Bate
Most botanists associate Autumn Lady’s-tresses with chalk downland but in my experience British plants are surprisingly catholic. I’ve seen them on flood banks of a fenland drain at near Tydd Gote in Cambridgeshire, on damp acidic lawns in the New Forest, on parched limestone grassland surrounding Morecambe Bay and in a tightly mown lawn of a suburban garden. 

Whether acid or alkaline, the common factor is a short, open sward and a lack of soil fertility. Like many other threatened plants, it needs freedom from competition. Remove grazers or add nutrients and taller, more nutrient-demanding species rapidly take-over.

I have a special affection for this lovely little orchid. In the early 2000s, the late Terry Wells asked me to help him monitor a population of Autumn Lady’s-tresses at Knocking Hoe National Nature Reserve in Bedfordshire. How could I refuse! 


Knocking Hoe
Image: P. Stroh
Knocking Hoe is home to a glittering cast of rarities - Moon Carrot, Pasqueflower, Field Fleawort, Spotted Cat’s-ear, Burnt Orchid, - to name but a few. But it was the Autumn Lady's-tresses that Terry chose to study back in 1962 (Wells, 1967). Having just returned from Jamaica, Terry had started working for the Nature Conservancy at its new experimental station at Monks Wood near Huntingdon. At a bit of a loss to know what to do with him, his new boss gave him a Land Rover with instructions to head off into the wilds of England and start researching grassland ecology. That he did and the rest, as they say, is history.

Terry & Kevin surveying
at Knocking Hoe

Image: P. Stroh
Terry always had a passion for orchids but it was the work of Carl Tamm in Sweden that inspired him to study their population dynamics (Tamm, 1972). Terry used Tamm’s ‘triangulation method’ for accurately relocating individuals within a fixed grid thereby allowing him to follow their fortunes in response to changes in management, climate and rabbit numbers. Terry’s interest in Autumn Lady’s-tresses was sparked by another Monks Wood legend, Franklyn Perring, who worked on Autumn Lady’s-tresses during the hot summer of 1955. Due to the drought, lawns were left uncut leading to numerous reports of Autumn Lady’s-tresses flowering in gardens, some of which were reported in The Times. Never one to miss an opportunity, Franklyn wrote a letter back, with Max Walters his co-author of the Atlas of the British Flora, calling for details of further sightings which he later published as a paper (Perring, 1956).

Terry monitored the Autumn Lady’s-tresses at Knocking Hoe from September 1962 until his death in 2008. A group of us have recorded them ever since, so 2020 marks the study's 58th anniversary. Over that time thousands of individuals have been painstakingly monitored, revealing fascinating insights into their private lives (see Walker et al., 2015 for a nice summary!). We now know that, although most live for about a decade, some survive into their 40s and even 50s. Even more surprising is their capacity to survive below ground only to re-appear a year or two later, presumably when they have captured enough nutrients, courtesy of their fungal partners, to flower again. 


Lynne Farrell (on left): formerly Botanical 
Assistant at Monks Wood, now BSBI President, 
has been a key member of the Autumn
Lady's-tresses survey team at Knocking Hoe

Image: P. Stroh
Studies that chart the intimate details of the lives of plants in this way are extremely rare and so it is an honour to carry on the study. We’ll be at Knocking Hoe on the 10th and 11th of September this year so if you are in the neighbourhood please drop in for a socially-distanced chat – we’re easy to spot amongst the marker flags!

Another place I associate with Autumn Lady's-tresses is Hambury Tout above Lulworth Cove in Dorset. This is the first place I saw them in the mid-1990s, growing in the downland above the cove. The day we visited was searingly hot and I vividly remember the throngs of tourists plodding up the motorway path to Durdle Door. Our goal was much nearer at hand and I have a treasured photo of Autumn Lady’s-tresses framed by Stair Hole. We went back for a family holiday a few years ago and they were still there dotted across the hillside, as well as on the down above our little cottage on the other side of the cove.

Autumn Lady's-tresses on
Wilverley Plain, New Forest,
Hampshire
Image: L. Bersweden 
As I keep saying, one of the consolations of lockdown has been getting to know our own backyards better. So it is good to see reports of Autumn Lady’s-tresses in gardens as well as on heaths, downs and dunes. Take a look at this tweet by Maureen Millar on the Isle of Wight and this one by 'Orchid Newbie' in Wales, both of whom have been lucky enough to have Autumn Lady's-tresses come up in their gardens. 

Like the summer of 1955, a lack of mowing this year has probably allowed them to flower in places they have always been. Or maybe we are in the midst of a genuine increase? As a species more at home in the Mediterranean, it seems a likely candidate to expand its range as a result of climate change; and these populations turning up in odd places like car parks, industrial estates and gardens may be the first signs that times are a-changin’ for this lovely little orchid.

References
Bersweden, L. 2017. The Orchid Hunter: A Young Botanist’s Search for Happiness. Short Books, London.
Dunn, J. 2018. Orchid Summer: in search of the wildest flowers of the British Isles. Bloomsbury Publishing, London.
Perring, F.H. 1956. Spiranthes spiralis (L.) Chevall. in Britain, 1955. Proceedings of the Botanical Society of the British Isles 2, 6-9.
Tamm, C.O. 1972. Survival and flowering of some perennial herbs. II. The behaviour of some orchids on permanent plots. Oikos 23, 23-38.
Walker, K.J., Stroh, P. Farrell, L. Carey, P. & Bellamy, G. 2015. Long-term monitoring of Autumn Lady’s-tresses Spiranthes spiralis (L.) Chevall. at Knocking Hoe, Bedfordshire. In:  R. Revells, C. Boon & G. Bellamy (eds.) Wild Orchids of Bedfordshire, pp.20-30. Bedfordshire Natural History Society.
Wells, T.C.E. 1967. Changes in a population of Spiranthes spiralis (L.) Chevall. at Knocking Hoe National Nature Reserve, Bedfordshire, 1962-65. Journal of Ecology 55, 83-99.

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