Carnivorous plants on North Morar

Carnivorous plants on North Morar

Part 1: introduction

On July 3rd 2022 I had a walk from Mallaig to the peak of Càrn a' Ghobhair in North Morar in the Scottish Highlands. My route took me north along the coast and around Cruach Mhalaig, then inland across the moors to a scramble up to Càrn a' Ghobhair's summit and then down to Loch Eireagoraidh and westward back to Mallaig via the north of Loch an Nostarie. Distance-wise, the hike wasn't particularly big, nor was there much elevation gain, but this is one of my favourite places. Most amazingly, I managed to find a whole seven species of carnivorous plant growing here.

I'm going to describe the species taxonomically, rather than chronologically through the adventure like I normally do, but I still want to relate it all back to my finds here (though my photos of carnivorous plants are from my sightings of them around the UK). The deviation from my usual style might make this a bit of a heavy read, but it's a really interesting topic I promise. I want to start with a description of this gorgeous part of Scotland.

1.1: what is North Morar?

North Morar is an area in the Highlands of Scotland, in the northwest of the Lochaber region, being very remote in comparison to Lochaber's main town: Fort William. Despite being remote, North Morar is a well-visited area due to the famous Jacobite Steam Train, which became especially famous after its use in the Harry Potter Movies around Glenfinnan, and which terminates in Mallaig, the main settlement on North Morar. This thin strip of land lies between Loch Morar, the UK's deepest lake, and Loch Nevis, a sea-loch branching inland like a fjord from the Sound of Sleat in the west. Due to this, North Morar is very nearly an island, being attached to the mainland by two thin stretches of land. To the west, Loch Morar runs into the sea via one of the UK's smallest rivers, the River Morar, via less than 1km before its estuary. Meanwhile, to the east, cutting off western North Morar from the eastern section, is a small glen between Loch Morar and Loch Nevis, about 1km long, known as Glen Tarbet - tarbet is a Scottish Gaelic word referring to thin/short stretches of land between two water bodies, similar to the Greek-derived English word 'isthmus'.

While North Morar is a small area, I still find that it encapsulates what Scotland is to me, in its landscape, wildlife, and history.

North Morar is a low-lying area. West of Glen Tarbet, its highest point is just 548m above sea level (less than the UK's popular definition of land having to be over 2,000ft [610m] to count as a mountain). However, due to its high latitude up in the Scottish Highlands, and exposed position against the Sound of Sleat towards the open Atlantic Ocean, and between two large water bodies, the environment on North Morar is comparable to upland, mountainous areas elsewhere. Some species I would normally see way over 600m can grow at near sea-level here, and the glacial landscape abundant with glacial erratics and steep rocky slopes, with scattered lochs and peat bogs on the moors make this area as mountainous as any other in Scotland as far as I'm concerned.

Aside from a few small trails into this area that tourists to Mallaig occasionally take for a short hike, North Morar's uplands are generally empty, and it is very easy even on a warm summer's day to walk for miles without seeing anyone, or any sign of human activity bar the notable deficit of trees, felled centuries ago. I've done a few decent sized hikes here so far, and some small strolls, with weather varying from blue skies with little fluffy clouds, to the kind of pouring rain shower that gets you soaking wet before you can even get your coat on, and thick fog that you can barely see a few metres through.

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1.2: geology and landscape

First, I'll talk about the physical attributes of North Morar. While I won't go into details on the Caledonian Orogeny and other major events that led to Scotland's form and geology today, I'll go over some of the more basic and local aspects of the land.

The rock here is very ancient, even by rock standards. Sediments were laid in shallow waters here over 800 million years ago in the early Cambrian Period. Many centuries and a lot of pressure turns this to sedimentary rock such as sandstone, but this rock has been through a lot more throughout its lifetime than to leave us with just sandstone today. Various periods of strong tectonic (and therefore seismic and volcanic) activity have changed this rock through time; most notably, the Caledonian Orogenic Event, a continental collision which forced rocks together under extreme temperatures and pressures and formed an ancient mountain range. Such stresses on the rock changed its form from basic sedimentary sandstone to metamorphosed rocks known as psammites and pelites, becoming similar to schist and gneiss in places.

In much of North Morar these rock layers are at an angle such that the ones exposed at the surface further east underly those to the west, and this seems to be associated with the landscape we see today. The large area of bogs and lochs around Loch an Nostarie is formed of the Lower Morar Psammite (and quartzite) formation, while the higher-lying, more mountainous area to the east of here, with the highest peak west of Glen Tarbet - Càrn a' Gobhair, is made from the rocks underlying this formation, known as the Basal Pelite (and psammite) formation (photo 5 looks over the flatter western moorland to the mountainous east). Along with this, much later volcanic activity, associated with the opening of the Atlantic around 60 million years ago, lead to a variety of dykes forming as lava welled up via pre-existing faults in the rock. These thin sections of volcanic rock can be seen in the landscape via gullies and crags which form from erosion at the sharp margins between the dykes and surrounding rocks, though this isn't particularly noticeable on North Morar.

The Cretaceous volcanism is, however, visible in the views from North Morar. looking westward are three very distinct sites on the ocean: An Sgurr on the Isle of Eigg (photo 6), the mountains of the Isle of Rùm (photo 7), and the Cullin mountains of Skye (photo 8). An Sgurr is made up of columnar volcanic pitchstone from when lava flowed down an ancient valley. The surrounding softer basalt has since eroded, leaving behind the unique ridge shape that is basically an inverted valley. Rùm and the Cullin, on the other hand, are basically extinct volcanoes, with Rùm in particular still looking rather volcano-like at sunset.

While geology inevitably affects the landscape, North Morar, much like most of northern Britain, has been heavily affected by glaciation over the past few million years. At such high latitude, northern Scotland held onto its ice sheets for longer than the rest of the UK, with over 1km of ice overlying the landscape just 11,000-10,000 years ago. This landscape of ice and snow nurtured glaciers of immense size, which flowed at unperceivable rates down into the sea, gouging out vast trenches that we now call U-shaped valleys, often filled with lochs. The larger glaciers carve the valley bottom down to below sea level, leaving behind sea lochs such as Loch Nevis bordering North Morar to the north. Meanwhile other large glaciers which didn't carve to the sea as entirely, leave behind deposits of everything they've scraped from the landscape in terminal moraines, such as what can be found at the western end of Loch Morar, helping to separate it from the sea. Such gouging by glaciers has also left Loch Morar with incredible depth, being the deepest lake in the UK, and 17th deepest in the world. After the last ice age, not only did the melting glaciers leave behind a landscape of fjords and lochs partially separating North Morar from neighbouring land, but the great weight that was lifted from the land here has also since led to it raising higher (over 20m in places) out of the sea. This is known as isostatic rebound, and has caused part of the coast of North Morar to contain short cliffs, with little water-worn caves and even rounded pebbles, despite being far out of reach from the tides today.

The land on North Morar itself has also been heavily affected by ice, with smaller glaciers carving steep-sided valleys with lochs such as around Loch Eireagoraidh, and depositing large glacial erratic boulders all over, along with boulders fallen from crags.

Part 2: Carnivorous plants

Now that I've done a quick overview of North Morar's physcial geography - a coastal area with craggy hills and glacial valleys, formed of low-grade metamorphic sandstone-based rocks, I can't wait any longer to describe my favourite finds from the area - the carnivorous plants.

This landscape of glacial basins, atop not-so-porous rocks in comparison to others such as limestone, coupled with North Morar's very rainy position on the western coast of Scotland (and oceanic climate), promotes boggy conditions. Small lochs fill with sediment, and mosses such as Sphagnum species retain huge quantities of water, allowing vast bogs to form. The soil is so sodden in places that bacteria and other decomposers can't function due to lack of oxygen (anoxic conditions), leading to a build-up of a plant-based soil known as peat. Such environments are harsh for plants to grow in, with acidic conditions, and low nutrients (particularly nitrogen, which is usually fixed by bacteria) for growth.

Plants have adapted in a variety of ways to cope with such a lack in nutrients, including the most famous solution: carnivory, also called zoophagy. This allows plants to gain nitrogen and other recourses absorbed from animals, rather then the soil, while still being able to use the sun for photosynthesis.

In the UK, three main carnivorous plant groups are found natively: the butterworts, the sundews, and the bladderworts. Of these, and excluding hybrid species, North Morar harbours both of the native butterwort species (P. grandiflora is native to Ireland, but though to be introduced in its few British sites, and it is speculated that P. alpina's one site may also be due to introduction), all three native sundew species, and at least one of the bladderwort species. Along with this, there are other carnivorous plants native to the UK, though they are less well-known and their form of carnivory less widely-recognised, such as another species I'll describe from North Morar later.

Butterworts

While there are exceptions, the following is true for most butterworts, including those native to the UK:

butterworts (genus: Pinguicula) are plants which grow from a central bud above poorly-developed roots. Their leaves generally grow outward and lie flat against the ground once fully developed, forming a rosette. These leaves are fairly rigid and succulent, and are often a bright yellow-green colour, or may have a pinkish tinge. It is the yellowish colour, along with the greasy appearance due to the mucilage described in a bit, that may give butterworts their name; like fatty, greasy butter the 'wort' part is found commonly in plant names and is basically an Old English word meaning 'plant'). The Latin 'pinguis', meaning fat also relates to this, and was later incorporated into the genus name for butterworts: Pinguicula.

The undersides of the leaves are smooth (glabrous), while the upper sides of the leaves, ignoring the mucilage, would appear to be coated in tiny hairs, made up of a stalk cell per hair protruding from the leaf, capped with secretory cells. The few secretory cells atop the large stalk cells form what are known as peduncular glands (a peduncle is a stalk that holds something, normally a flower or inflorescence, though not in this case), and they secrete a thick, gluey (mucilaginous) substance that forms tiny droplets atop each stalk, giving the leaves a wet appearance. This look may attract insects in search of water (the leaf colouration may also aid in attracting prey), and the droplets are definitely capable of ensnaring small invertebrates, who get stuck on the leaves. The insects will die from their respiratory spiracles getting clogged by the mucilage (which is produced in excess upon contact with the insect, releasing additional mucilage that was stored in reservoir cells at the base of the stalks), suffocating them (if they don't die from exhaustion trying to get away first).

In order to absorb the nutrients from the trapped insects (and also pollen and other protein-rich plant parts which may fall on a butterwort leaf, making them omnivores), butterworts need to digest them. The mucilage from peduncular glands does contain small amounts of digestive enzymes, but these aren't intended to fully digest the animals. Instead, the small amounts that are digested from this provide the plant with an initial boost in nitrogen, which is detected by the plant and triggers enzyme release by sessile glands that lie flat on the leaf below the stalks. It is these enzymes that digest most of the insect's body, with, for example, esters, phosphates, and proteins being digested by esterase, phosphatase, and protease. This breaks them into smaller components that can be absorbed into the plant through holes in its outer cuticle layer (cuticular holes), usually leaving behind the hard-to-digest exoskeleton of the insects, made of chitin, on the leaf's surface. These cuticular holes would normally be bad for a plant, as the cuticle helps to contain water within them so preventing desiccation, but the boggy and humid habitats that promotes carnivory anyway, also means such drying out isn't a huge issue in their natural environments.

Despite the predatory tendencies of butterworts, they still form symbiotic relationships with insects to help them in pollination in reward for nectar. Butterwort flowers are held on stalks relatively high above the leaves to avoid having potential pollinators subsequently die to the plant. The flowers are commonly between violet and white in colour, depending on species, and have five petals, often arranged unevenly around the flower (three clustered on one side, two on the other), in a similar fashion to other species in the Lamiales order, which includes mints and similar herbs, along with bladderwort.

Common Butterwort (Pinguicula vulgaris)

Vulgaris literally means 'common' (which is unfortunately where we get the word 'vulgar' from, referring to things that are only for common people). This butterwort is the most common of the UK butterwort species, and among its most common carnivorous plants. It is found in peat bogs and similar habitats through most of the UK, only becoming somewhat rare in central and southern England. As such, this is a species I come across frequently. Common butterwort has recognisable yellowish leaves that curl upwards at the margins, and deep purple flowers. It is harder to find in winter; found only as a hibernaculum, a large dormant bud that will regrow into the butterwort in the coming spring.

Around North Morar this species is easy to find, in boggy areas, especially on soil rather than among Sphagnum, though it can thrive on both. Even small patches of soil on rock with a wet flush over it will do, with a preference for areas that aren't too crowded by larger bog vegetation.

Pale butterwort (Pinguicula lusitanica)

If, like common butterwort, pale butterwort's scientific name meant the same thing as its English, it would be Pinguicula pallens. Instead, 'lusitanica' is a description of this species' unique distribution. Lusitania was an ancient Roman Province that mostly includes modern-day Central and Southern Portugal on the Iberian Peninsula, named after the Lusitani people. It has since been used to refer to a seemingly random assemblage of plants known as the Lusitanian Flora, all linked by their similar and confusing distributions. There are fifteen plants officially listed as part of the Lusitanian assemblage, all seemingly endemic to the Iberian Peninsula and southwestern Ireland. Such a distribution is hard to explain, and there are many theories suggesting that the Irish ones might have survived in sheltered pockets through the last Ice Age, or that very early human activity back in the Bronze Age may have led to their transport over the sea on badger pelts and other trade items, though the topic is up for debate. Pinguicula lusitanica isn't in this core group of Lusitanian plants as its distribution is a bit more extensive, but it follows a similar pattern. This species' distribution extends from the Iberian Peninsula and Ireland to include Morocco to the south, along with western France, Northern Ireland, southwestern England (around Cornwall), and western Scotland, suggesting to me that the distribution of Lusitanian Flora might be natural rather than human-induced, with species such as the pale butterwort having spread further over time in comparison to other species with a Lusitanian distribution.

Pale butterwort is easily distinguished from common butterwort by is pale pink flowers with a yellow centre, who's five petals are spread a little more evenly around the flower, each with a two-lobed tip, similar in shape to typical primrose flowers, though they usually droop downwards so it is hard to tell. When not flowering, pale butterwort forms smaller leaf rosettes than common butterwort, unable to get much growth in as it often dies after just one year. The leaves also have a purple-pink tinge to them, with notable darker veins, unlike common butterwort's bright yellow-green. The leaf shape is also different, often appearing more rounded at the tip because the margins roll greatly upward and inward revealing the smooth underside and providing a succulent rim to the leaf surface even more so than with common butterwort. When this species does push through the winter, it does so in its normal leafy form, with no hibernaculum.

I didn't find this species on my first trip on North Morar, but on my second time I found it to be quite abundant in patches, from the coastal valley just up from Mallaigmore, to the banks of Loch Eireagoraidh and north of Loch an Nostarie. It is often harder to find than common butterwort, not just because it is rarer and smaller, but also because it is much happier growing among other peat bog vegetation such as grasses and small sedges, often being hidden from view until you're very close.

Sundews

Sundews (genus: Drosera) are a group of carnivorous plants in the Droseraceae family, which also includes Venus fly-traps and waterwheels (which are also carnivorous and have a similar trap mechanism to Venus fly-traps). They come in a variety of different growth forms, but many of them are endemics from Australia, while the northern temperate, and subtropical sundews are more uniform. The leaves of these plants are held on petioles (stalks), with the petioles being much longer and clearer compared with butterworts whose petioles are often unnoticeable, appearing as though the leaf sprouts directly from the centre of the plant. However, similarly to butterworts, sundew leaves are coated in glandular tentacles. While butterworts' hairs are small, mostly made up from an elongated stalk cell, sundew tentacles are multicellular, even incorporating plant vascular tissue through the centre of the tentacle, allowing resources to be circulated through the tentacle so they can easily grow much larger than butterwort hairs. These tentacles even vary in length across a single sundew leaf, with short central tentacles on the leaf surface, transitioning through larger outer tentacles to the very long marginal tentacles, which extend from the sides of the leaf, flexing backward a little, allowing increased reach and a larger trapping area. A peduncular gland (the whole tentacle - stalk and gland, is known as a stalked gland) surrounds the tip of each tentacle, secreting mucilage in what appears like drops of morning dew, which gives sundews both their English name (plants which retain dew even in the sun), and their scientific name: 'drosos' (δρόσος) being Greek for 'dew'. Invertebrates are attracted to the refreshing-looking, sweet secretions, and possibly also the reddish colour of the tentacles (though some studies suggest this isn't the case), and subsequently get stuck and proceed to die from exhaustion in trying to escape, or asphyxiation as mucilage clogs their spiracles. Then, similar to how butterworts do it, sessile glands on the leaf's surface (and also on the surface of the tentacle stalks, since they are multicellular), release digestive enzymes, breaking down the insect's components to be absorbed into the leaf.

Along with their impressive tentacle and mucilage-drop size for catching larger and more prey, most sundews are also capable of moving their tentacles to bring an insect in towards the centre of the leaf, and in contact with as many stalked glands as possible. Some butterworts can also do something like this, bending their leaf margin inwards slightly by thigmotropism, a directional growth movement in response to touch stimuli to bring more glands in contact with the insect, but it is a much lesser effect. Sundews, on the other hand, rely on thigmonasty, a response to touch which induces movement not by growth, but by other changes, such as how a decrease in turgor pressure on one side, and increase on the other, can cause cells to shrink and swell, allowing features to bend at a much faster rate than with thigmotropism. Tentacles can bend around prey in less than a second in Dorsera glanduligera, and while the UK species are much slower than this, it is still notable speed for a plant. Many sundew species are even able to bend and curl their leaves to further surround prey to maximise contact for increased digestion and absorption rates. The exact mechanisms for all these thigmonastic responses in sundews are not fully known, and there are likely many, but one mechanism found within the tentacles' bending is as follows:

mechanical stimulation by touch onto a tentacle causes electrical action potentials to be fired off, which travel down the tentacle and are terminated before they reach the rest of the leaf. As action potentials reach cells on the far side of the tentacle from the touch, they affect auxin, a plant hormone, which induces protons to be pumped out from within the cell though the cell membrane and into the cell wall, reducing the pH of this area to make the wall of the cell more acidic such that a type of protein in the walls known as expansin changes shape, relaxing and allowing for an increase in cell volume via osmosis and turgor, swelling the cells on this side and so bending the tentacle in the opposite direction, towards the touch.

As with butterworts, sundews also develop flowers that are pollinated by insects and held high above the leaves to avoid predating their pollinators. These flowers aren't solitary like in sundews, but rather grow as an inflorescence along a stalk, with each flower bud along the stalk opening after the last, and so increasing how long the plant is in flower for. Flower stalks may also branch into two separate inflorescences, which mirror each other and look very cool. The flowers are usually white or pink (all UK species are white) and small, with 5 petals and radial symmetry most of the time, like a fairly 'normal' flower. Also similarly to common butterwort, temperate sundews form hibernacula over winter, which appear not like a bud, but rather as a knot of tightly curled young unfurled leaves.

Round-leaved sundew (Drosera rotundifolia)

Among the most common and widespread carnivorous plants in the northern hemisphere, round-leaved sundew can be found across much of northern Europe, through Russia, to Japan and Korea, and over much of North America. It is widely distributed in the UK, often in mountainous areas, but also just wherever peat bogs form, especially on Sphagnum mosses, and is the UK's most common sundew species. Round-leaved sundew is a small plant with a rosette growth form that has a diameter between 3 and 5cm, lying largely flat against the ground, and with rounded leaves held on the petioles that are often less than 1cm in diameter. These rounded leaves give the species both its English and scientific name (rotundifolia - think 'rotund foliage', means round leaf).

Drosera rotundifolia, while small and common, has played a large role in our understanding of carnivorous plants. It is the first plant to be truly confirmed as carnivorous following a series of studies by Charles Darwin, which he published in his book: Insectivorous Plants in 1875. The studies here helped him with his theory of natural selection as he paid attention to the adaptations that have allowed carnivorous plants to survive in harsh conditions, although he did write in 1860 that 'at the present moment, I care more about Drosera than the origin of all the species in the world.'

Oblong-leaved sundew (Drosera intermedia)

Oblong-leaved sundew is also a wide-ranging species, similar to round-leaved sundew, but excluding most of round-leaved sundew's Asian distribution, and stretching down the Americas as far as northern South America. In the UK, this species is widely distributed, but usually much less abundant than round-leaved sundew. I often find it is more capable at growing on bare wet peat when compared to round-leaved sundew's tendency to grow on moss, and as such, I've only seen it on North Morar on bare boggy bits around the path north of Loch an Nostarie. Drosera intermedia has oblong leaves, often described as spatulate, which are small, though the overall plant can be much larger than round-leaved sundew, especially since its petioles hold the leaves semi-erect, rather than flat against the ground as in Drosera rotundifolia. Oblong-leaved sundew was first described in 1798, but I haven't found an online copy of the publication. I think 'intermedia' in the species name (meaning 'intermediate') may be naming this species in reference to its intermediate morphology between Europe's two other sundews, Drosera rotundofolia and Drosera anglica.

Great sundew (Drosera anglica)

For the most part, D. anglica, sometimes also called English sundew in relation to its Latin name, has a distribution similar to that of round-leaved sundew, just a little more restricted and rarer. It was originally commonly associated as one with Drosera intermedia, both under the now unused name Drosera longifolia. Despite being a notably larger plant with longer leaves, and with it being described as a separate species as early as 1778, the collective term D. longifolia was only officially rejected as recently as 1999. Great sundew is the largest of the three European sundew species, with leaves up to 3.5cm long, and held nearly 10cm tall on the most erect petioles. Being the largest European sundew, this species can also feed on much larger insects than oblong and round-leaved sundew, though it still mostly sticks to smaller prey. damselflies, small butterflies, and even some dragonflies have been found caught by a great sundew, immobilized in the sticky mucilage. Drosera anglica is also a particularly good example of thigmonastic leaf movements, as its leaves curl to a great extent around its prey to help further the digestion process.

Genetics:

Interestingly, great sundew has twice as many chromosomes as most sundew species, with 2n=40 (1n=20 for sex cells like pollen). This would suggest that it has arisen as a hybrid species. In most cases hybridisation normally leads to an infertile or otherwise unviable lineage, preventing speciation in this way. However, one form of hybridisation is allopolyploidy, also known as amphipolyploidy, whereby a mistake occurs in meiosis that leads to gametes (sex cells) that retain the full paired genome of the pairent plant (2n) rather than half. These gametes normally fuse with ordinary gametes, leading to a 3n hybrid plant that is infertile, but if two 2n gametes fuse, or further meiosis mistakes occur in the hybrid (first generation hybrids often have relatively high rates of unreduced gamete [2n] formation) to give a similar result, then a new plant can be formed that has paired chromosomes again, though twice as many (4n is called tetraploid, but we still refer to them as 2n, and the parent species may have already been more than diploid anyway, making it some form of polyploidy beyond tetraploid). This new hybrid plant, that has all the genes of both parents and therefore twice as many chromosomes as either individual species, is often larger and more robust than the parent plants, often with intermediate traits between the two, though it doesn't always turn out this way. Hybrids like this also can't breed back with either parent species due to the difference in chromosome number, making them reproductively isolated and therefore an entirely new species. In Drosera anglica's case it is thought that such hybridisation took place in North America between Drosera rotundifolia and Drosera linearis, forming the great sundew whose greater adaptability from D. rotundifolia allowed it to spread much more successfully than its large parent: D. linearis from whom it got its size, now being distributed outside of North America, including on North Morar in Scotland.

On North Morar I have found Drosera anglica growing in peatbogs across the lower basin west of the main hills, often standing in areas too waterlogged for other sundews, holding its stalks high above the water's surface. While it prefers mossy peat bogs like the others, especially similar to round-leaved sundew, great sundew is also more tolerant of calcium, and so may grow in somewhat more rocky areas too. I've not observed this on North Morar yet, but I have seen it growing on damp sandy patches on the banks of the nearby Loch Shiel.

Bladderworts

In his book 'Insectivorous Plants', Charles Darwin noted that some carnivorous plants have compartmentalisation in their leaves. Some parts are used in digestion, while other parts help with absorption of the digested matter. He speculated that specialisation to one over the other of these might lead to alternative trap, digestion, and absorption methods, with the other original function being lost completely. This would explain how bladderworts, a relative of butterworts, have evolved to use a completely different trapping method to them. Bladderworts (genus: Utricularia) are very different from their butterwort cousins. Their vegetative parts are not clearly separated into leaves, stems and roots, with many different parts being able to contain photosynthetic pigments, and much of the plant being found below ground or underwater. For the most part, bladderworts can be divided into two major sections: terrestrial and aquatic, though aquatic varieties arose through multiple different co-evolving groups of bladderwort, making it a paraphyletic group. These all contain bladder-shaped traps that give the genus its common English name and also its scientific name (derived from 'uter' - a small leather container, similar to where 'uterus' comes from). These traps are smaller in terrestrial species, being found beneath waterlogged soil where they may catch tiny rotifers and protozoans (microorganisms). Aquatic species have much larger bladders, able to catch larger (though still very small) prey such as water fleas and midge larvae, though even young tadpoles are known to have been caught.

The trapping mechanism via the bladders of Utricularia species are widely credited as the most sophisticated structures in the plant world. These tiny structures are attached to the bladderworts' stolons (these are stem-like) and react to mechanical stimuli from potential prey. The bladderwort actively transports water out of the bladders, causing the walls to be sucked inwards, straining them elastically against their natural bulbous shape. Once no more can be pumped out due to osmotic pressures, the trap is set, with no water being able to get in through the entrance due to its 'door' being stuck to a small mebrane on one side called the velum. However, on the door are small hairs known as trigger levers, and any slight touch to them will move the door, breaking its seal to the velum and allowing water in. The difference in pressure between inside and out (it's basically a vacuum seal) means that water will instantly rush in, with the door flying open, and the bladder trap springing back to its open state, drawing in even more water, all within around 0.01 seconds. If a small creature were to trigger the hair, it would instantly be sucked in with the water and trapped inside the bladder, where it is digested by secreted enzymes. Even larger prey, which don't fit in the trap, may have their tail sucked in, enough to trap them and lead to them getting ingested a bit at time, though they need to be thin enough sticking out of the trap so that it can return to its sealed position to draw them in further.

Bladderworts have some of the most beautiful flowers of all carnivorous plants, held on very thin stalks and with just two large petals, the lower one forming an especially large lower lip. Often the only part above water/ground, these flowers can vary a lot in colour, but all native UK species are yellow, and are often compared to small yellow snapdragons. Bladderworts can self-pollinate, reducing the need for insect attraction so the flowers are often closed, but they can also use insects for pollination too, with large showy flowers, and with no known pattern between when closed self-pollinating flowers grow and when flowers that do open for insects grow.

Bladderworts are widely distributed in the UK, though are sparse in much of England. They thrive in acidic pools of water often around peat bogs, but can withstand higher pHs and be found in much larger water bodies in places. There are acutally seven native bladderwort species in the UK, but they are difficult to tell apart, especially when not in flower. These are: Utricularia intermedia, U. minor, U. vulgaris, U. australis, U. stygia, U. ochroleuca, and U. bremii (see here for some identification information).

Nordic bladderwort (Utricularia stygia)

On North Morar so far, I have found bladderwort in some small pools, barely more than puddles, a little north of Loch an Nostarie not far from the main path. These plants grow in very shallow water in the bogs, already helping to suggest against U. vulgaris and U. australis, which prefer free-floating in larger bodies of water. The relatively few bladders present and flattened 'leaves' coming from the stolons also suggest against the U. minor aggregate, leading to the tentative diagnosis of this bladderwort being part of the Utricularia intermedia aggregate. This is a group of species once all thought to belong to the species Utricularia intermedia but have since been recognised as separate. In Scotland, it turns out that U. stygia and U. ochroleuca are the most common in this group, with U. intermedia from which they were split actually being quite rare. Of these, the National Biodiversity Network shows a record of Utricularia stygia around Loch a' Bhada Dharaich on North Morar, seen by Ian Strachan in 2007, so my sighting is likely also this species, though I can't confirm.

A carnivorous liverwort?

All the species mentioned previously are what are generally recognised as all the carnivorous plant species in the UK (excluding protocarnivorous plants). However, the world of bryophytes (mosses, liverworts, and hornworts) is often overlooked and dismissed. Bryophytes are non-vascular plants, lacking many of the features later-evolving plants gained that allow larger/taller growth and better desiccation protection. As such, these ancient plant lineages are often small and restricted to damper areas. Despite this, bryophytes are by no means rare or lacking in diversity and complexity. Over 1,000 species can be found in the UK alone. In fact I found nearly 150 species within walking distance of my home in Lancashire over the course of around 3 years, and over 20 species within four hours in a woodland in Cornwall.

Of the bryophytes, two liverwort genuses in the UK, Colura and Pleurozia are known to have unusual water sacs in their leaves, which were often interpreted as being for water storage. There were some ideas about carnivory as an alternative function as early as 1893, but this wasn't confirmed until a Colura species from Kenya was studied in 2000 (see here), making it the first known carnivorous liverwort, and the first known carnivorous bryophyte. This provoked a later study in 2005 into carnivory in the Pleurozia genus (here). The species studied was Pleurozia purpurea, which can be found on North Morar, and was studied from specimens collected around Scotland.

Purple spoonwort (Pleurozia purpurea)

Purple spoonwort grows as branching, worm-like shoots with leaves pressed against the stem. These often lean or are held diagonally with a drooping tip, with a pair of larger leaves drooping over the upper side, and tiny pear-shaped leaves forming sacks on the underside on the stem. The colour is often quite striking with this species, and while it can be greenish, it may also vary from a deep purple to a bright red-orange colour. In the UK, this bog and mountain species is distributed entirely in Northern Ireland and North and West Scotland, with no records from England or Wales. The whole species is sterile, spreading only via vegetative propagation and unable to form spores, though tubular organs thought to be sterile perianths can be found. As such, its wide-ranging distribution in oceanic northern Europe, Bhutan, China, western Canada, and Alaska is thought to be a relict distribution.

Small sac-like leaves for water storage are known from a variety of liverworts, such as the scaleworts (Frullania). However, Colura and Pleurozia are unique in having a moveable lid on their sacs, comparable to the lid of bladder traps in Utricularia. The pear-shaped water sacs of purple spoonwort are only open via a tiny round gap, just 300 micrometres (0.3mm) in diameter, at the base of a concave depression on the ventral side of the leaf that forms the sac. Here, a valve of dead cells is fixed to some living basal cells that form a hinge, allowing the dead cell valve to be moved to block-off the hole and close the sac, opening inwards with a similar mechanism to Utricularia. Experiments using the ciliate Blepharismas americana (a microorganism) showed that multiple ciliates could enter the sacs when introduced with the liverwort, and that none of them ever escaped the sac, showing it is effective as a trap. There was also evidence in experiments that the ciliates are attracted to the liverworts and then get trapped, further suggesting that carnivory is the main function of the sacs, although there are a variety of somewhat unrelated reasons that could also lead to ciliates being attracted to the liverwort. Along with just the ciliates used in the experiment, spoonworts cultivated in sphagnum rather than in sterile conditions, and those taken directly from the wild were found to have many more species abundant in their leaf sacs, further suggesting carnivory just based on abundance, and also included much larger species such as tardigrades, copepods, and even small mites. The extent of zoophagy in these liverworts is still debated, but whatever the case, it is a fascinating topic to follow.

Part 3: Conclusion

I hope this was interesting to read, I certainly find it interesting to learn and absolutely love going out and exploring to find these unusual species. This one was a little heavy on the biology, and I think in future I'd like to stick to my more chronological story-telling style, like bringing you along on my adventures, but I'll see what happens. I'll keep the conclusion short since everything else was so long. Basically: thanks for reading!