Irish Plant Carnivores

Round-leaved Sundew aka Common Sundew (Drosera rotundifolia), Killarney National Park. The leaves bear numerous modified stalks or "tentacles" tipped with clear droplets of sticky dew giving rise to the common name.

Not surprisingly, Charles Darwin made the first scientific study of carnivorous plants.  He began his 1875 pioneering work, entitled the "Insectivorous Plants", with a detailed examination of Drosera rotundifolia (pictured above).  Perhaps the most widespread of Ireland's 3 native Sundew (Drosera species), Darwin stated, "it was soon evident that Drosera was excellently adapted for the special purpose of catching insects." And further, "As this plant is extremely common in some districts, the number of insects thus annually slaughtered must be prodigious"!

All Sundew species included here (and studied by Darwin) share similar characteristics.  Each has leaves that appear reddish due to the presence of numerous stalked glands (or modified hairs). The stalks produce clear, sticky "dew".  The gland tipped stalks (which Darwin referred to as "tentacles") are typically longer and, perhaps, more concentrated on the leaf margins. Presumably this provides a larger trapping zone to aid in capturing prey. Much shorter stalks are found in the center of the leaves (see image below). Darwin found that stimulating a single tentacle (such as with a small piece of meat) caused it to bend inward, while the others nearby remained upright.  However, when the meat reached the leaf itself adjacent tentacles often "pour forth an increased amount of secretion" that becomes highly acidic.  Overall, Darwin believed, "the absorption of animal matter from captured insects explains how Drosera can flourish in extremely poor peaty soil".  

Round-leaved Sundew (Drosera rotundifolia) with digested prey remains at Bray Head, Ireland. The blackened insect remnants no longer produce enough stimulus to keep the tentacles pressing inward; according to Darwin these remnants will "be blown away by a breath of air" and the stalks will then re-secrete dew and be ready to clasp a new object once a new droplet of dew has formed. 

Drosera rotundifolia is the smallest of Ireland's sundews, and Great Sundew (Drosera anglica) is the largest. As the images below show, Great Sundew's leaves are much more elongated, to approximately 1" in  length, but share similar "tentacle" characteristics including the lengthier gland-tipped stalks around the margins, and reduced stalks mid-leaf. 

Great Sundew (Drosera anglica) with captured and partially digested prey. The longer stalks along the top of the leaf are bent downward and inward holding the prey, and bringing the item into contact with the smaller glands on the leaf front surface which are believed to produce digestive enzymes (See Lloyd, 1942, Carnivorous Plants). 

Great Sundew (Drosera anglica) with captured Mayfly. Unlike the previous image, the Mayfly is held against the back of the leaf, and digestion may not be possible due to the lack of necessary glands along this surface.

Great Sundew (Drosera anglica) - Note: back of leaf appears smooth & green, although minute glands are present barely visible to the naked eye. By far the longest and most well developed "tentacles" originate from the leaf margin where they aid in trapping.  

Great Sundew (Drosera anglica) has relatively large size and aggressive "tentacles" that, perhaps, enable it to catch larger prey items, such as the MayFly shown in the image above.  But in other respects, Darwin's study concluded that "the tentacles of Drosera anglica behave like those of Drosera rotundifolia."

The final of Ireland's 3 sundews is called Drosera intermedia. As the species name suggests, it lies between the other two in terms of leaf size, and shares characteristics of both species.  One trait thought to be indicative of Drosera intermedia is the branched, leafier stem, as shown in the image below. Assuming my ID is correct, nearly all individuals of this I observed were growing in open, shallow water "bog pools".  

Oblong-Leafed Sundew (Drosera intermedia), along Bog Road, Ireland

Patch of Oblong-Leafed Sundew (Drosera intermedia) in bog pool along Bog Road, Ireland

The second major group of carnivorous plants I include here are the Butterworts.

Butterworts (Pinguicula species) trap insects with "flypaper-like" basal leaves, which lie flat on the ground. There are 3 native, extant Butterwort species in Ireland. A 4th species, Alpine Butterwort (Pinguicula alpina), is considered extirpated, having not been found in Ireland since approximately 1912. I was lucky enough to see each of the extant species.

Butterwort leaves (presumably P. vulgaris) with partially digested prey items. All Pinguicula species share characteristic  compact, basal leaves like these, with some variation in size, and sometimes in color. They are invariably slightly incurved along the margins which Darwin believed helped prevent insects from being washed away by rainwater.

As the previous image shows, a number of different insects can be found attached to Pinguicula leaves. Darwin summarized numerous instances of insect capture on Pinguicula vulgaris (image below) and found that the glands secrete acid which "has the power of dissolving animal substances" and absorbing the result.  He said, "there can be no doubt that it profits by its power of digesting and absorbing matter from the prey which it habitually captures in such large numbers."  Interestingly, Darwin believed Pinguicula vulgaris also draws nourishment from pollen, leaves, and other plant parts adhering to its leaves, making it in part a "vegetable feeder."!

Large Flowered Butterwort (Pinguicula grandiflora), Killarney National Park, Ireland. In Darwin's time this species was considered a"sub-species" of P. vulgaris. 

Pale Butterowrt (Pinguicula lusitanica) near Bray Head, Ireland. The most different of the Irish Butterworts, with the much smaller almost transparent basal leaves and the pure white flowers.

Common Butterwort (Pinguicula vulgaris) near Famine Village, Ireland. I'm basing the tentative identification of this on the non-overlapping lower petals. 

A final look at Butterwort, this image taken near Caragh Lake, Ireland has a much paler petals than typical Large Flowered Butterwort.

You could spend your life searching for these species in their native habitats and it would not be a wasted life. 

For Peat's Sake: Turbary Rights & destruction of human created ecosystems?

I was lucky enough to be able to explore some very interesting habitats in western Ireland. Exactly what to call them, is unclear to me.  However, I believe the example shown above, could be referred to as a "Blanket Bog".  The Cottongrass (Eriophorum sp), drew me to the site, and initially suggested wetness (given my previous assumptions) but many examples I traipsed across were surprisingly dry.  The example shown below, was dramatically wetter, much more sphagnum moss was evident at the surface, pockets of almost open water were present, and the surface was really unstable and even dangerous to walk across. I think of this habitat as a "quaking bog".  In an upcoming post, I intend to show some of the interesting plant species I observed in both situations. From hereon, I lump both of these together as "peatlands" or bogs.

An example of early bog mapping in Ireland
(https://www.bordnamonalivinghistory.ie/maps/history-of-maps/)

The extent of Irish bogs was unknown until the early 1800's when a nationwide mapping effort began (image right) with the clear intention to make these areas more useful or productive.  But it wasn't until the 1930's, that Ireland's Department of Industry and Commerce began to actively plan for the development and use of these otherwise "worthless" landscapes.

A Turf Development Board was  established with the goal of developing a turf industry and operating & draining bogs. These efforts proved fortuitous during WWII, when turf became an essential alternative fuel source when coal imports were heavily diminished. Thousands of acres of bogs were eventually drained and actively harvested, sometimes with workers in on-site residential camps. Today at least one "semi-state" run corporation continues industrial-sale harvesting of peat , supplying an estimated 12% of Ireland's electricity  (https://www.sciencedirect.com/science/article/abs/pii/S0264837712000129).  This corporation just announced plans to cease all peat harvesting by 2028 (https://www.irishtimes.com/news/environment/bord-na-m%C3%B3na-not-climate-change-deniers-over-impact-of-peat-1.3696808)

In the meantime, turf cutting also continues for personal uses. The image below shows recently cut and stacked turf for use by a single family.

The right to take or cut turf is considered a "common right" or "turbary right" that involves a complex legal system that has led to many disputes.  The gentleman I spoke with about the operation above indicated his family had been cutting turf in this area (or exercising his turbary rights) for several generations. I came to see this much like a family woodlot maintained for cutting firewood in other areas of the world. Undoubtedly, dried peat or "turf" remains a primary fuel source for some Irish households. During my visit, it was not uncommon to smell peat fires burning in the morning and evening. I found published estimates of the number of households relying on turf ranging anywhere from 1 - 20% of Irish households.
(https://www.sciencedirect.com/science/article/abs/pii/S0264837712000129) (https://www.livescience.com/38498-ban-on-turf-cutting-peat.html)

I observed numerous "small scale" harvest operations, such as those above, with turf either being harvested or being laid to dry.  And then, I finally came to understand some of the unusual patterns I had been noticing and couldn't previously understand, in places where the harvest was not so recent. (see below).

Historic, subtle evidence of turf cutting near Caragh Lake, Ireland. 
Green arrows indicate approximate boundaries of former cuts

Historic evidence of turf cutting near Ballycroy National Park, Ireland.
Green arrows point to remnant former surface height

Most instances of both current and former harvest I observed were like those above, with regular harvest boundaries and harvest depths. Most also appeared to have more peat depth available to harvest in the future. However, a few other sites were very irregularly cut for reasons unclear to me, such as the deeply incised bog surface near Kerry, Ireland (note stacks of drying turf, and patches of Cottongrass, see below).

A few other examples had been extracted to depth exposing stump fields. These "stump fields" presumably represent woodlands that were destroyed by humans several thousand years ago.  Although the pattern of landscape change may vary locally, region-wide , "various evidences indicate that most of the areas now covered by blanket bog once carried woodland in the first half of the Holocene.  (http://www.paper.edu.cn/scholar/showpdf/NUz2ANxIMTD0YxeQh)

What caused the loss of the historic forests whose stumps are now exposed? 

According to the paper cited above (and numerous other sources), Neolithic farming & burning practices (between 4,000 - 5,000 years ago) were responsible for the initial decline and loss of woodland. This means early humans with stone tools (and fire) began extensively clearing forest. By the early Bronze age the job was essentially finished! 

Over the generations that followed, the bogs developed and blanketed over vast areas formerly occupied by forests.  In the end, "increased human activities" were the major cause of blanket bogs establishment! Thus, these bogs are "anthropogenic communities" created by the Irish ancestors.  I can't think of many other examples where a truly man-made vegetation type has become the object of conservation interest.

  

How much should we be concerned about  destroying something we previously created?