Ancient Woodland Indicator Species: Wood Anemone

A typical flower of Wood Anemone, Anemone nemorosa
© Karen Netto (Andrews)

The Wood Anemone, Anemone nemorosa, is a popular feature of spring, broad-leaved, deciduous woodlands. Although described by Linnaeus in 1753, many discoveries about this native member of the Ranunculaceae or Buttercup family are relatively recent. I was initially surprised that a much-loved plant on home soil should be so poorly understood. In efforts to understand the flower better, I pieced together a jigsaw puzzle of information from various European research sources.

Abundant Wood Anemone is considered a good indicator of an ancient woodland. Its solitary presence should not lead to an automatic assumption as to the age of the wood. It features in Francis Rose’s list of ancient woodland indicators for the South West, South East, South and East Anglia. A Woodland Trust Report also recognises it as one of the most frequent and prominent species in UK ancient woodland indicator lists. The Wood Anemone takes an inexplicably long time to fully establish. It is noted for poor migration from its original location. The National Biodiversity Network (NBN) Atlas’s 2017 data shows that the Wood Anemone is a species of Least Concern with over 31,000 UK records. Is the apparent abundance in a restricted, threatened habitat causing a blind spot?

Anemone nemorosa can spill over outside woodland. It is also favoured by garden designers and gardeners. There are hybrid and naturalised species. In most of my local observations, the wild species have been confined to the centre of the wood. It is almost as if there is a no man’s land in operation at the edge of woods. I hypothesised that it might be another unfortunate indicator of the degradation of local woodland soil due to nearby agricultural practices. My research has revealed that other factors may potentially be at play.

Resistance to Recolonisation

Wittig’s German research study describes efforts to reestablish the Wood Anemone in an area of previously high air pollution. It failed to establish a permanent plant community despite experiments with three different soils after improvements in air quality. Soil acidification and contamination were seen as irreversible in the short term, despite the plant flourishing in other woodland nearby.

The failure to establish a new plant community seems to carry implications for the creation of future woodlands. It also raises questions about the feasibility of the planned translocation of ancient woodland flora to make way for new infrastructure. The Wood Anemone exposes how little we understand about how ancient woodland floral communities function nearly 3 centuries after Linnaeus’s Species Plantarum.

Most resources refer to the Wood Anemone’s ability to spread via underground rhizomes. You might be forgiven for thinking that an Anemone, named for the daughter of the wind or as the Windflower, is wind-pollinated. I was surprised by the conflicting evidence on the Wood Anemone’s reproduction. It initially appeared that research has been hampered by greater interest in exotic, foreign species. Cursory evidence on pollinators has been taken as the end of the story for far too long. Pointers from learned botanists of an earlier age have been ignored or forgotten.

Short Flowering Season

Perhaps the Wood Anemone is its own worst enemy? It is not an easy plant to study. Wild flower guides point to flowering between March and May. The plants that I discovered flowering in mid-March had disappeared back underground before late April this year. Its companion plants were still present and new species had succeeded it in other locations. The window for carrying out research on our native Wood Anemone is limited. Changes in phenology due to climate change are likely to make it even more unpredictable. The woodland vegetation was also affected by changes in the canopy in my local woodland. There were several hefty tree casualties during the severe winter storms. Perhaps a warm, sunlit spring enabled the plant to complete its life cycle more quickly?

Carpet of Wood Anemones, Anemone nemorosa, in a Somerset ancient woodland © Karen Netto (Andrews)

Morphology

Closed, half-closed and drooping heads of Wood Anemone, Anemone nemorosa, in overcast weather conditions. Nodding, petaloid sepals protect the stamens in poor weather conditions. © Karen Netto (Andrews)
Public domain botanical illustration of Wood Anemone, Anemone nemorosa

Rhizomes, Seeds and Dispersal by Ants

The botanical drawing on the right illustrates the following:

  1. Anemone nemorosa with white/pinkish petaloid sepals with multiple, spirally-arranged stamens. It has palmately-lobed leaves that grow on the upper part of the stem (cauline) rather than at the base. It has creeping horizontal underground rhizomes.
  2. After flowering, nodding carpels in a spiral contain both viable and abortive seeds
  3. Seed with fleshy outgrowth known as elaiosome or caruncle. An elaisome is a fat body attached to the seed. It attracts the attention of ants who help ensure the dispersal of its seeds. Seed dispersal by ants is known as myrmecochory.

Illustration above right by: Swedish botanist C. A. M. Lindman (1856–1928), taken from his book(s) Bilder ur Nordens Flora (first edition published 1901–1905, updated edition 1917–1926?).

Inefficient Dispersal

While the Wood Anemone appears to have both rhizomes and seeds as dispersal mechanisms, it appears that neither method is efficient. This species has consistently proved to be the laggard in efforts to colonise new woods with shade-tolerant plants. This seems strange as rhizomes are often the reproductive choice of invasive species.

A Temperamental Species?

Natural colonisation rates are notoriously difficult to predict. Chosen species do not respect Man’s intended formula for creating new woodlands. Species compete and outcompete each other. The Wood Anemone appears to be one of the foremost species that dislikes high agricultural phosphate residues, low organic matter, soil compaction and poor soil structure. The loss, erosion or degradation of ancient woodland habitats point to potential serious declines in wild Wood Anemone colonies.

Poor Seed Viability?

Studying old botanical drawings alerted me to a long-reported issue with Wood Anemone seeds. It is regularly stated that Anemone nemorosa only reproduces via vegetative propagation from its rhizomes. Seeds are considered to be non-viable or abortive. Bower’s 1908 carpel illustration shows one developed and three abortive ovules. He theorises that this related to ‘imperfect representatives of a plurality of ovules in ancestry‘. Upon further investigation, I found a wealth of European research by other scientists reflecting on the apparent contradictions in past observations.

Immature Seeds

Lukianchuk’s Ukrainian study suggests that flowering only occurs an astonishing 10-12 years after sowing seeds. The Baskins give Anemone nemorosa as an example of a seed in which it is difficult to locate the embryo even when using a dissecting microscope. The embryo in freshly-matured seeds appears as a mass of undifferentiated cells. Rather than being abortive or non-viable, it appears that the Wood Anemone deliberately sheds immature seeds. Its seeds are released with a high moisture content. Moreover, it is not unusual for the seeds of moist temperate, woodland species to continue their maturation in the soil.

Germination Requirements

There is a tendency to believe that Wood Anemones go dormant after spring flowering. Mondoni’s Italian study reveals that the plant continues to grow underground continuously between May and September. Seed germination is finely tuned to climate. Seeds do not germinate in the summer months. A cold snap in late autumn and early winter is important for germination.

Climate Change Risk?

The Italian researchers alluded to the potential effects of climate change while avoiding pure speculation. There are three potential risks for Anemone nemorosa. Firstly, drier summers could dry out its seeds before germination. Secondly, a delay in harsh winter weather could fail to trigger germination. Finally, as a woodland species, it has a short growing season and is dependent on spring sunshine reaching the understorey. Delayed germination risks canopy closure before the Wood Anemone completes its life cycle. My own observations showed that the species benefited from severe 2019-20 winter storms opening up the canopy. This clearly demonstrates the difficulties of climate change predictions.

Rhizomes

Dependence on vegetative propagation is not an ideal reproduction system for any species, as it does not achieve a mix in the gene pool. Given that the Wood Anemone seems so reliant on rhizomes, it seems surprising that it does not spread further. It is possible that we are overlooking seeded Anemone nemorosa colonies in woods. Islands of flowers could offer evidence of ant dispersal. Only genetic analysis would reveal the truth. In the meantime, we may be misattributing some colonies to rhizomes.

The plant is poisonous. Its roots are reputedly acrid. So if they aren’t eaten and don’t go dormant in summer months, what is checking Anemone nemorosa’s progress? Apart from the soil conditions already mentioned, a fungus could be the culprit.

Anemone Cup

Dumontinia tuberosa, Anemone Cup, is a fungus that appears on bare ground with the Wood Anemone. It is a parasite of Anemone flower species that appears above ground in early spring. It attaches itself to the plants’ tubers. It is suggested that national recorders often mistake it for Jelly Ear fungi, Auricularia auricula-judae. The National Biodiversity Network has just 176 records of the Anemone Cup in the UK and of these only 11 are accepted records. It is believed that the species is underreported. Could this be a partial answer for the Wood Anemone’s failure to spread more widely? So many answers are frustratingly out of sight and underground for most of the year.

Wood Anemone Pollinators

So far, I have concentrated on botanical aspects of the Wood Anemone. To understand an ancient woodland species, it is important to take a more interdisciplinary approach. If you draw on information about pollinators and effective woodland management, the long-term plight of the Wood Anemone within ancient woodland becomes clearer. Anemone nemorosa necessarily becomes more reliant on rhizomes for reproduction, if it is only found deep in heavily-shaded woods.

Buglife highlights the importance of woodland rides for pollinators. Many woodland pollinators will not fly through shaded woods. They tend to prefer sunny east and south edges for early morning foraging. Mixing habitats and opening up the canopy will encourage them to venture further into woods. Their presence is notably encouraged by many of the maligned botanical species:

  • Hogweed, Heracleum sphondylium
  • Cow parsley, Anthriscus sylvestris
  • Thistles, Cirsium sp.
  • Knapweeds, Centaurea sp.
  • Ragwort, Jacobaea vulgaris (formerly known as Senecio jacobaea)
  • Brambles, Rubus fruticosus agg.

Management using a 3-5 year mowing cycle is recommended. It is important to leave shrubs to blossom too. This calls into question current practices of flailing such hedges every year beyond road safety requirements. Pollinators love:

  • Sallows/Willows, Salix sp.
  • Blackthorn, Prunus spinosa
  • Gorse, Ulex sp.
  • Hawthorns, Craetaegus sp.
  • Wild Cherry, Prunus avium and Prunus cerasifera
  • Crab apple, Malus sylvestris.

Hoverflies

Most resources cite Hoverflies as the Wood Anemone’s pollinators. I tried to find photographic evidence of Hoverflies on the flowers. I found just two examples behind pay walls. There are reportedly 280 Hoverfly species within Britain. Most members of the general public confuse Hoverflies with bees and wasps. Hoverflies deliberately use what is know Batesian mimicry to ensure that they are avoided by predators. They do not sting. They mimic bees and wasps. They are in fact beneficial insects. Gardeners may be delighted to learn that they gobble up aphids.

If the Hoverfly species in photographic evidence are correctly identified, then it would suggest that Eristalis tenax and Syrphus spp. are Wood Anemone species. Are there more species involved? It seems extraordinary that there is so little information on an essential plant-pollinator relationship. Does this suggest a shortage of pollinators or a lack of recording?

Bee-fly

Researchers at the University of Heidelberg revealed the Dark-edged Bee-fly, Bombylius major, as an unexpected, additional pollinator of Anemone nemorosa. Until this research, the flower was thought to solely be a source of pollen. These new observations led to a better understanding of the flower’s morphology. The scientists discovered the site of nectar secretion and nectary tissue.

The Bee-flies’ behaviour seemed extraordinary. They have a rigid, needle-like, non-retractable proboscis. It is designed to probe deep into flowers for nectar. Other nectar-rewarding flowers were present nearby. It was not a one-off event. Some bees are able to penetrate into nectary tissue; the Bee-fly’s proboscis is not able to cut into the tissue. Researchers discovered that the Bombylius major is able to suck up dried nectar by using saliva from its proboscis. In following up, the German researchers discovered copious nectar using dissecting microscopes on freshly-opened, early morning specimens. This deep probing for nectar can help to ensure the fertilisation of ovules in all carpels that might not be achieved by pollen alone.

Bee-flies have been the subject of a UK Citizen Science Watch project since 2016. The 2019 study saw a high peak in March. It is significant that the Bee-flies do not fly in temperatures of less than 16.5ºC or on dull days. At the time of writing, Bee-fly Watch 2020 has revealed 3,179 records of 3 species date with 2091 supporting photographs. The Dark-edged Bee-fly, Bombylius major, is the most common species in the UK.

Future Research?

My own photography has revealed an unidentified insect inside a Wood Anemone flower. I do not know whether it was there as a pollinator or to keep warm. Beetles are known pollinators for Magnolia species. My research into the Wood Anemone has revealed much more than I thought possible at the outset. It surprised me how little we understand above a much-loved, native flower and how disconnected much established research remains after publication.

My investigations leave many questions unanswered about how Anemone nemorosa will cope with the erosion of its ancient woodland habitat and climate change. Could genetic analysis reveal how successful its seeds are versus rhizomes? Are there sufficient populations of wood ants for effective seed dispersal? What are the optimal conditions for seed germination in the UK? Could Citizen Science provide more detailed records of its pollinators, especially Hoverflies? What more could be done to secure this much-loved spring flower for future generations?

Anemone nemorosa with insect visitor © Karen Netto (Andrews)

© Karen Netto (Andrews)

References and Further Reading

Baskin, Carol C. & Baskin, Jerry M. (2014): Seeds: Ecology, Biogeography and Evolution of Dormancy and Germination. 2nd Edition. Academic Press Inc. (p.10)

Blakesley, David & Buckley, Peter (2010): Woodland creation for wildlife and people in a changing climate. Principles and practice. Pisces publications. Newbury. (p.25 Colonisation of new woods by shade-tolerant plants).

Bower, F. O. (1908): The origin of land flora, a theory based on the facts of alternation. p. 144. Macmillan & Co. London. Flickr via Cornell University Library. Last accessed 25 April 2020.

Buglife (2019): Managing Woodland for Pollinators. Last accessed 25 April 2020.

Bungard, Stephen (2015): Anemone Cups. Plants of Skye, Raasay & The Small Isles Blog. 12 April 2015. Last accessed 2020.

Burton, V. J. (2020): Bee-flies are back! Citizen Science Blogs. 2 April 2020. Natural History Museum. Last accessed 25 April 2020.

Denisow, Bozena et al. (2016): Morphology of Anemone sylvestris. L. (Ranunculaceae). Acta Bot. Croat. 75 (1), 74–80, 2016. De Gruyter Open. Last accessed 19 April 2020.

Dipterists Forum (2020): Bee-fly Watch: results so far. Soldierflies and allies recording scheme. Last accessed 25 April 2020.

Erbar, Claudia & Leins, Peter (2013): Nectar production in the pollen flower of Anemone nemorosa in comparison with other Ranunculaceae and Magnolia (Magnoliaceae). Organisms Diversity & Evolution. Volume 13 (3) September 2013. Last accessed 19 April 2020.

Featherstone, Alan Watson (2020): Spring in Strathfarrar, part 2 – flowers galore. Alan’s Blog. 31 August 2017. Last accessed 19 April 2020.

Fowler, Alys (2014): Keep your Anemones close. Life and style. The Guardian. 8 March 2014. Last accessed 25 April 2020.

Glaves, Peter et al. (2009): A Survey of the Coverage, Use and Application of Ancient Woodland Indicator Lists in the UK. A Report to the Woodland Trust. Sheffield Hallam University. Last accessed 24 April 2020.

Harris, J. C. (2018): With the Windflowers – Anemone Cup. Mushroom Diary Blog. April 2018. Last accessed 19 April 2020.

Harrison, Marie (2015): Beetles and Their Role in Pollination. Dave’s Garden. 23 April 2015. Last accessed 19 April 2020.

Harvey, Martin C. (2020): Identifying soldierflies and allies: bee-flies in genus Bombylius. Soldierflies and allies recording scheme. Version 1 at 15 March 2020. Dipterists Forum and Biological Records Centre (BRC). Last accessed 25 April 2020.

Lukianchuk, Anna et al. (2017): Wood anemone. Anemone Nemorosa L. Analytical review. Science Rise: Pharmaceutical Science Journal. 27 June 2017. Last accessed 23 April 2020.

Mondoni, Andrea et al. (2008): Habitat-correlated seed germination behaviour in populations of wood anemone ( Anemone nemorosa L.) from northern Italy. Seed Science Research Journal. Volume 18. 1 December 2008. Last accessed 23 April 2020.

National Biodiversity Network (2017): Anemone nemorosa L. Wood Anemone. NBN Atlas. Last accessed 21 April 2020.

National Biodiversity Network (2017): Dumontinia tuberosa (Bull.) L.M. Kohn. Anemone Cup. NBN Atlas. Last accessed 19 April 2020.

NatureSpot (?): Dark-edged Bee-fly. Recording the Wildlife of Leicestershire and Rutland. Last accessed 25 April 2020.

NatureSpot (?): Hoverflies. Recording the Wildlife of Leicestershire and Rutland. Last accessed 25 April 2020.

Newton, Rosemary et al. (2013): Seed development and maturation in early spring-flowering Galanthus nivalis and Narcissus pseudonarcissus continues post-shedding with little evidence of maturation in planta. Annals of Botany.

Plantlife (2020?): Wood Anemone (Anemone nemorosa). Last accessed 21 April 2020.

Reilly, Pat & Parker, Sue (1995-2020): Anemone nemorosa L. – Wood Anemone. First Nature. Last accessed 19 April 2020.

Reilly, Pat & Parker, Sue (1995-2020): Auricularia auricula-judae (Bull.) Wettst. – Jelly Ear Fungus. First Nature. Last accessed 25 April 2020.

Reilly, Pat & Parker, Sue (2005-2007): Wonderful Wildflowers of Wales, Volume 1 – Woodland and Waysides. First Nature (p.13).

Richard, Claude & Jani, Annick (2019): Anémone des bois, anémone Sylvie. Fleurs sauvages de l’Yonne. L’herbier virtuel icaunais de Claude Richard. Last accessed 19 April 2020.

Rose, Francis (1999): Indicators of ancient woodland. The use of vascular plants in evaluating ancient woods for nature conservation. British Wildlife. April 1999. (pp. 241-7). Last accessed 24 April 2020

Royal Society for the Protection of Birds (RSPB) (?): Hoverfly. What is Batesian mimicry and other Hoverfly facts. Last accessed 25 April 2020

Scottish Wildlife Trust (?): Wood Anemone, Anemone nemorosa. Species Profile. Last accessed 25 April 2020.

Wildlife Trusts, The (?): Wood Anemone. Scientific name: Anemone nemorosa. Last accessed 25 April 2020.

Wittig, Rüdiger (2008): Experimental Research on Recolonisation of Anemone nemorosa of the Beech Forests of the Ruhr district (Germany) floristically impoverished by Air Pollution. Environmental Science Pollution Res. Int. 2008 September; 15(6): pp. 492-8. Last accessed 21 April 2020.

Woodlands.co.uk (2011): Seeds, ants and dispersal. Blog author: Lewis. Flora & Fauna Blog. 12 August 2011. Last accessed 25 April 2020.

Woodland Trust (?): Wood Anemone. Anemone nemorosa. Last accessed 22 April 2020.

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