• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

Alan Watson Featherstone

ECOLOGIST, NATURE PHOTOGRAPHER AND INSPIRATIONAL SPEAKER
FOUNDER OF THE AWARD-WINNING CHARITY TREES FOR LIFE

  • Home
  • Public speaking
  • Writing
  • Photography
  • Events
  • Shop
  • Blog
  • About me
  • Contact

A twinflower day

Cairngorms National Park: 15 July 2020 12 Comments

A twinflower day
Twinflower (Linnea borealis) in flower in Upper Port Wood in the Cairngorms National Park on 12th July 2020.

With the travel restrictions that have been imposed as part of the COVID-19 response, it’s been over four months since I was able to get out to any of my favourite places in the Caledonian Forest, such as Glen Affric. By 10th July, when those limitations were relaxed in Scotland, I was keen to reconnect with the forest and its seasonal phenomena. Top of my list was the opportunity to see twinflower (Linnea borealis), one of the rare plants in the Caledonian Forest, in blossom.

Twinflower (Linnea borealis), with no sign of flowers, at a site in Glen Affric in late June 2017.

There are only a few tiny patches of twinflower in Glen Affric, and I’ve never seen them flower there, although I’ve visited them at the right time of year for that – late June and early July. However, there are some sites in the Cairngorms National Park where the species is more abundant, so it was one of those, at Upper Port Wood near Grantown-on-Spey, that I was heading for on my first trip out after the lockdown travel restrictions had been eased.

Twinflower flowering en masse in Upper Port Wood in late June 2017.

I’d been introduced to that site in 2017 by Andy Scobie, an ecologist who had done a PhD on rare plants in Scotland, including twinflower, and who subsequently was the Project Officer for the Cairngorms Rare Plants Project, which included twinflower as one of its four target species. When I’d visited Upper Port Wood with Andy in late June 2017, I’d been astonished at the abundance of twinflower there.

Twinflowers in bloom in Upper Port Wood on 12th July.

Ideally I would have liked to return to the site in the last week of June, as that is when the peak of flowering takes place, but the five mile limit on journeys to get out into Nature for exercise was still in force, and it precluded that, as Upper Port Wood is about 30 miles from where I live. However, when I arrived there on 12th July I saw straightaway that there were still plenty of plants in flower, even though it was obviously past the maximum, with shrivelled blossoms visible amongst those that were still fully open.

Twinflower plants at the base of the trunk of a Scots pine (Pinus sylvestris) in Upper Port Wood.

By carefully focussing on the plants with the freshest-looking flowers I was able to appreciate twinflower’s beauty anew, and get some reasonable photographs.

Detailed view looking into one of the blossoms of a twinflower plant.

It was a good day for doing close-up photography, which usually requires long exposures to get an acceptable depth of field. There was a gentle breeze but it was intermittent, with calm spells in between when the delicate flowers stayed motionless for long enough to provide an opportunity to take clear and sharp images.

Some years ago I wrote a Species Profile about twinflower, and that’s available on the Trees for Life website here. The species has a circumboreal distribution, meaning that it occurs all around the world at northern latitudes, in the boreal forest zone.

Twinflower in blossom in the Upper Incommapleux Valley in British Columbia, Canada.

I’ve seen it flower in great profusion in other northern countries, including Norway and Canada, so it’s always saddened me that it’s so rare in Scotland.

Twinflower blossoms in a birchwood, Nordstedalen, Sogn og Fjordane, Norway.
Twinflower in amongst cowberry (Vaccinium vitis-idaea) at the base of an old Scots pine in Invereshie and Inshriach National Nature Reserve in the Cairngorms National Park. The twinflower stolon or runner can clearly be seen arching across the cowberry leaves.

The problem with twinflower is that it is self-incompatible, meaning that one plant cannot pollinate itself – at least two plants are required for cross pollination and seed production to take place. However, in Scotland today twinflower has been reduced to isolated patches, often separated by very large distances, with each patch possibly consisting of a single clonal individual which has spread vegetatively over time, via above-ground runners known as stolons. In this it is somewhat similar to aspen (Populus tremula), which also often occurs as isolated clonal individuals and therefore rarely produces seeds in Scotland. Whereas aspen is wind-pollinated, twinflower relies on flies, hoverflies and bumblebees for pollination, but these insects will not usually travel for the kilometres that may separate different twinflower patches, so seed production is rare.

Stolon of twinflower at the base of the trunk of a Scots pine in Upper Port Wood.

Twinflower is highly susceptible to ground disturbance, with the stolons easily being damaged, and it is also quickly destroyed by fire. As a result, it has disappeared from most of the Highlands along with its native Caledonian Pinewood habitat, due to forest exploitation, burning and clearance for agriculture. Because of its reliance mainly on vegetative reproduction, it cannot easily recolonise areas from where it has been lost, and this has led to its rarity in Scotland today.

Twinflower in blossom in 2017 in the Trees for Life tree nursery at Dundreggan Conservation Estate in Glenmoriston.

While I was the Executive Director of Trees for Life the charity initiated a project to propagate and plant out some of the rare woodland flowering plants of the Caledonian Forest, including twinflower. Cuttings were taken from the sites where it survives in Glen Affric and propagated at the charity’s tree nursery at Dundreggan, with the intention being to establish some new populations at suitable sites in Affric. Another aim was to enrich the existing populations there by planting out twinflowers in them that had been grown from the other sites, thereby hopefully getting around the self-incompatibility problem that limits natural seed production.

Leaves of a twinflower plant beside a fallen Scots pine cone in Upper Port Wood.
This is a significant part of the tiny remnant population of twinflower near Coire Loch in Glen Affric.

That project is still ongoing and it will hopefully help to boost the twinflower population in Glen Affric, as well as establishing some new areas of twinflower in other nearby pinewood remnants. It would be great if one day the twinflowers in Glen Affric can rival the density and abundance of the species in patches like the one in Upper Port Wood.

Here in Upper Port Wood, these twinflowers are growing beside a cowberry plant (Vaccinium vitis-idaea) with red leaves, indicating it has been infected by the cowberry red leaf fungus (Exobasidium vaccinii).

While I was looking at some of the twinflowers this week I noticed a few discoloured leaves on a cowberry plant (Vaccinium vitis-idaea) beside them. I recognised the red patches as indicating the presence of the cowberry red leaf fungus (Exobasidium vaccinii), a species which induces the production of unusual, brightly-coloured galls on the leaves (and occasionally the stems) of cowberry. The red blisters visible in this photo are the early stages of the development of the galls.

On this cowberry plant, the gall induced by the cowberry red leaf fungus is more advanced, and the cup-like shape is beginning to form.

As the fungus becomes more established, each gall takes on the form of a distorted cup shape, sometimes becoming larger than the rest of the leaf it is growing on. The cups are usually red on their upper surfaces and white underneath, where the fungal spores are released from. Strangely enough, it seemed to me as though the red and white of the fungus complemented (and enhanced) the pink and white flowers of the twinflower plants they were growing beside.

Here the fungal gall is more than double the size of the rest of the cowberry’s leaf. Some twinflower leaves are visible in the bottom right of the image.

As I looked around, I spotted more and more examples of the cowberry red leaf fungus at various stages of development on different cowberry plants, in amongst the twinflowers.

The cup-like shape of the cowberry red leaf fungal gall is very obvious in this example.
Several leaves on this cowberry plant have been infected by the redleaf fungus, while the red-stemmed stolon or runner of a twinflower plant is visible below. 

Like all gall-inducing organisms Exobasidium vaccinii is a parasite, utilising the cowberry plant for its own gain, without giving anything back in return. The exact mechanism by which gall-inducers stimulate their host plants to produce specific growth forms, such as these cup-like shapes, is not clearly understood. Possible explanations that have been proposed include the action of chemicals or hormones secreted by the gall-inducing organism, or the transfer of genetic material from the gall-inducer to the host plant by means of endosymbiotic bacteria. The subject of gall formation is one that is ripe for further research, having not been prioritised in the past by the reductionist approach of science, which has focussed mainly on looking at organisms in isolation from each other. Gall formation is a classic example of an ecological relationship – it is the interaction between the different organisms involved that produces such dramatic results.

Bright pink galls induced by the birch gall mite (Acalitus longisetosus) on the leaf of a downy birch (Betula pubescens).

Interestingly enough, just a few feet away from the cowberry red leaf galls I spotted another very visible example of plant galls. There was a young downy birch tree (Betula pubescens) growing beside the path, and as I passed it I noticed some dark pink shapes on a few of its leaves. I recognised these as galls that are induced by a mite – I’ve seen (and photographed) them before in Glen Affric.

Closer view of the galls induced by the birch gall mite (Acalitus longisetosus) on the downy birch leaf.

The mite is known as the birch gall mite (Acalitus longisetosus) and there are relatively few records of it in the UK, although it is almost certainly more widespread than they indicate. The main cluster of records is in the Scottish Highlands, including the Cairngorms National Park and Glen Affric, with a few others scattered across England and Wales. The pink spherical structures that form the gall are collectively called an erineum, and the mite larvae develop inside them. Some further information about the species is available here.

Yellow dark-veined birch aphids (Calaphis flava) on the underside of a leaf of the downy birch tree.

While I was looking at this young birch tree, I turned over a few of the new leaves at the ends of its twigs, to see if there were any aphids there. I’ve had a longstanding interest in aphids, and in the past three months have taken the opportunity afforded by the COVID-19 lockdown to develop that considerably, mainly by looking for, and finding, lots of different aphids in my garden and on the trees and wild plants near my house.

Yellow dark-veined birch aphid (Calaphis flava) giving birth to a live nymph on the underside of a leaf of the downy birch.

Almost immediately, I found some aphids on a few of the newly-opened birch leaves, and was able to identify them later (using the excellent Influential Points website as a reference) as being a species called the yellow dark-veined birch aphid (Calaphis flava). I’d not seen this particular species before, so I was very pleased to find them here, especially when I noticed one that was giving birth.

Another view of the yellow dark-veined birch aphid (Calaphis flava) giving birth to a live nymph.

Part of my fascination with aphids is due to their remarkable lifecycle. This includes not only reproduction by laying eggs (as most insects do), but also during part of the year (typically in the spring and early summer) by parthenogenetic means, whereby a female does not need to mate with a male in order to produce young. In this stage, a female gives birth to a live nymph, which is basically a miniature version of herself. Even more remarkably, the newborn nymph will already have the developing embryo of the next generation growing inside her. This phenomenon is called ‘telescoping of generations’ and is the means by which aphid populations can build up very quickly.

Black-tipped dark-veined birch aphid (Calaphis betulicola) on a petiole or leaf stem of the downy birch.

As I continued to look around this young birch I spotted another aphid on the stem of one of its leaves. This was a different, but closely-related species – the black-tipped dark-veined birch aphid (Calaphis betulicola). It’s differentiated from its near-namesake by the fact that it has dark flanges or tips to its siphunculi (the upward pointing protuberances near the rear of its body, that are used for excreting alarm pheromones, wax or defensive chemicals when it is threatened).

Mine made by the larva of a micro-moth (Stigmella lapponica) in a leaf of the downy birch.

Although this was a small birch tree, being only two metres or so in height, there was plenty of life on it, including a convoluted mine that I noticed on one of its leaves. This was the work of the larva of a micro-moth (Stigmella lapponica), which had grown from an egg laid on the leaf by a female moth. Once it had hatched out, the larva burrowed its way through the leaf, between the upper and lower cell layers, feeding as it did so. The brown line in the centre of the mine is frass – the waste product excreted by the larva. When it was fully grown the larva would have pupated and the new adult micro-moth would have emerged to fly off and find a mate, leaving this distinctive linear pattern in the leaf as the tell tale sign of its development there. Many different micro-moths make mines in leaves, with five different species of Stigmella alone occurring on birch leaves.

Small downy birch aphids (Betulaphis quadrituberculata) on the underside of a leaf of a silver birch (Betula pendula).

By this time I’d been in Upper Port Wood for about four hours, but had spent all of that time in an area of about 100 square metres, where the twinflower occurs in abundance, because there had been so much of interest there. I decided to walk a little further into the wood for the remaining hour or so that I had available, to see what else I would find. As it turned out, I only went about another 30 metres before my eye was drawn to another young birch tree, this time a silver birch (Betula pendula).

Small downy birch aphids (Betulaphis quadrituberculata) on the underside of leaf of the silver birch, with one in the lower right giving birth to a nymph.

Looking underneath a few leaves led almost immediately to me finding some more aphids – a different species called the small downy birch aphid (Betulaphis quadrituberculata). As their common name indicates, these are very small aphids, with the adults (the largest ones in this photo here) measuring a maximum of two millimetres in body length. They were present on the underside of a few leaves, and in one case I spotted an adult giving birth to a nymph.

Small downy birch aphids (Betulaphis quadrituberculata) and the egg of a predatory syrphid hoverfly on the underside of a leaf of the silver birch.

Aphids feed by sucking phloem sap from the leaves, stems and twigs of trees and plants. They do this by inserting their hypodermic needle-like rostrum into the plant to reach the sap, and this effectively fixes them in place while they feed. Because of this, they are very vulnerable to predators, which include small birds such as the chiffchaff (Phylloscopus collybita). To reduce the risk of predation, the vast majority of aphids feed on the underside of leaves, to make them less visible to birds, and therefore requiring interested people like me to search for them there! However, aphids have many other predators as well, and an adult syrphid hoverfly had laid an egg beside one group of the aphids, which would provide easy pickings for the hoverfly larva when it hatched out. In situations like this, I’ve observed that the aphids continue feeding as usual, seemingly completely oblivious to the danger they are in.

Winged birch aphid (Euceraphis sp., probably Euceraphis betulae) on the underside of a leaf of a silver birch.

There were quite a few young silver birches growing together beside the path, and on another one I found a different aphid species again. This was a winged adult aphid, much larger than those I’d seen before, and with an obvious dusting of blue-tinged wax on its antennae and legs. I recognised it immediately as being one of the Euceraphis birch aphids – there are two closely related species, one of which is more commonly found on downy birches and the other on silver birch trees. I guessed this one would most likely be the silver birch aphid (Euceraphis betulae), but it requires examination under a microscope to differentiate between the two species.

All too soon, it was time to head for home again, even though I hadn’t gone more than a few hundred metres into the wood. On my way back, I stopped once more to appreciate the twinflowers, knowing that it would probably be in June next year when I have another chance to enjoy their delicate and graceful blossoms.

There’s something very elegant about the shape and alignment of the blossoms of twinflower that set it apart as something special and different from the other flowering plants in the forest.

(with thanks to Rob Edmunds for his assistance in identifying the micro-moth that made the mine in the downy birch leaf).

Unseen biodiversity of Glen Affric, part 3
Life on a spear thistle

Tagged With: aphids on birch trees, Cairngorms National Park, Caledonian Forest, Linnea borealis, plant galls, Twinflower

Reader Interactions

Comments

  1. Linnea Andersdotter Rundgren says

    3 February 2021 at 9:33 am

    Thank you for a beautiful and detailed tale of the flower with which I have resonated since I was birthed into this world, and consequently named after (yes my parents are biologists). I love these wonderful, tiny, yet vast expressions of the life force, that meander through the forests around my home, with a glowing iridescence on a bright midsummer night.

    With love,
    Linnea

    Reply
    • Alan Watson Featherstone says

      3 February 2021 at 11:25 am

      Hi Linnea,

      Thanks for your positive comments and feedback, and you have a wonderful name! You write very beautifully too – your phrase “a glowing iridescence on a bright midsummer night” is very evocative.

      With best wishes, Alan

      Reply
  2. Cornelia Featherstone says

    20 July 2020 at 12:21 pm

    Dear Alan,
    what an amazing blog – I think it is fabulous how much joy and inspiration, knowledge and fulfilment you can find in all these small things. It sounds like a very happy day indeed.
    xxxCornelia

    Reply
    • Alan Watson Featherstone says

      20 July 2020 at 12:36 pm

      Thanks Cornelia – it’s one of many happy days I’ve had out in Nature recently, and I’ll be posting more blogs about some of them soon. XX Alan

      Reply
  3. John Lowry says

    17 July 2020 at 3:37 am

    Greetings Alan — read and thoroughly enjoyed your blog. Found the information about the twinflowers of particular interest as I am very interested in wildflowers. Glad you are able to get out on your excursions and thank you for sharing them with us. So much to see, experience and appreciate.

    thanks again

    Reply
    • Alan Watson Featherstone says

      20 July 2020 at 11:32 am

      Hi John, thanks for your comment and feedback – I’m guessing that twinflower may occur in some of the forests near you in Ontario? I hope you’re coping well with the COVID-19 lockdown, and are getting out into Nature in your area. With best wishes, Alan.

      Reply
  4. Friederike Goedecke says

    16 July 2020 at 4:32 pm

    It´s always a wonderful experience and great fun to take a walk with you, even if it is only a few meters. I’m so glad you’re back !

    Reply
    • Alan Watson Featherstone says

      16 July 2020 at 4:41 pm

      Many thanks for the feedback Friederike – I’m glad to know that my blogs are appreciated!

      With best wishes,

      Alan

      Reply
  5. Joy Waddington says

    16 July 2020 at 9:47 am

    Fascinating, thanks. It’s good to read about the small beings which are all part of the importance of biodiversity.

    Reply
    • Alan Watson Featherstone says

      16 July 2020 at 10:39 am

      Hi Joy,

      Thanks for leaving this positive comment – it’s good to know you found the blog fascinating and informative.

      With best wishes,

      Alan

      Reply
  6. Stephen Burchett says

    16 July 2020 at 4:58 am

    Hi Alan, a great blog, informative and beautifully illustrated. Liked how each item led on to a new story of the natural history in the region.

    Reply
    • Alan Watson Featherstone says

      16 July 2020 at 10:38 am

      Hi Steve,

      Many thanks for the feedback – I’m glad you liked the blog.

      With best wishes,

      Alan

      Reply

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Primary Sidebar

My TEDx talk – Restoring the ancient Caledonian Forest.

TEDx TEDx – Restoring the Caledonian Forest

Recent posts

  • A shieldbug extravaganza, part 2
  • A shieldbug extravaganza, part 1
  • Life on a spear thistle
  • A twinflower day
  • Unseen biodiversity of Glen Affric, part 3

News

  • ‘A Rewilding Journey’ workshop scheduled for 28 August – 4th September 2021
  • Interviews for the Accidental Gods podcast series
  • Beavers are still facing an uncertain future in Scotland
  • The Nature Talks: Reconnecting People and Planet Now More Than Ever
  • Trees and Bees Conference 19 March 2021

I’m speaking at…

  • Online presentation to the Elders Action Network, 6th June 2021 – 6 June 2021
  • A Rewilding Journey: Rewilding the World and Ourselves – 28 August 2021–
    4 September 2021

Over on Twitter…

Alan Watson FeatherstoneFollow

Alan Watson Featherstone
AlanWatsonFeat1Alan Watson Featherstone@AlanWatsonFeat1·
14h

Even if there were no other valid & compelling reasons for Scotland to become independent, this alone would be sufficient cause. Additional nuclear weapons being installed in Scotland without public knowledge or consent is an outrage against democracy.

The Ferret@FerretScot

In 2018 @NukewatchUK estimated three new #nuclear warheads arrived at Coulport on the Clyde. Then nine in 2019, and 13 in 2020.

https://theferret.scot/sleekit-increase-trident-nuclear-warheads/

Reply on Twitter 1383173344225267720Retweet on Twitter 13831733442252677204Like on Twitter 138317334422526772016Twitter 1383173344225267720
AlanWatsonFeat1Alan Watson Featherstone@AlanWatsonFeat1·
23h

From Siberia to the Amazon & Borneo, forest fires are a major cause of the biodiversity crisis, often for agriculture. "in India most of such fires are deliberately caused by people mainly for agricultural purposes" We need planet-friendly agriculture! https://www.bbc.co.uk/news/world-asia-india-56671148

Reply on Twitter 1383041402414727168Retweet on Twitter 13830414024147271683Like on Twitter 138304140241472716816Twitter 1383041402414727168
AlanWatsonFeat1Alan Watson Featherstone@AlanWatsonFeat1·
23h

This is an excellent article about @royhdennis in the Guardian today. I've known Roy for many years & he's one of those rare people who just gets on & does inspiring, positive work for nature, not letting bureaucracies & mainstream inertia stop him. https://www.theguardian.com/environment/2021/apr/16/conservation-legend-roy-dennis-were-facing-an-ecological-crisis-but-its-exciting-too

Reply on Twitter 1383037091907518471Retweet on Twitter 13830370919075184711Like on Twitter 13830370919075184717Twitter 1383037091907518471
Load More...

Copyright © 2021 Alan Watson Featherstone | Wikipedia | LinkedIn