How spots are formed

According to Study.coms post on patterns in nature, pattern is defined as, “a consistent form, design, or expression that is not random”.  The patterns that are favoured by natural selection will become common across a species, but how do these patterns come about?

Six spot burnett moth Zygaena filipendulae showing spots

Alan Turing explored this problem in “The Chemical basis of morphogenesis” in 1952.  He discovered that chemicals moving across embryonic cells cause patterns.  There are activators (which increase the amount of two chemicals which mix together to create dark pigment).  And there are inhibitors (which decrease the concentration of the two chemicals, prohibiting production of pigment.)  When this occurs in alternating areas you see spots.   The colour is produced by melanophore or chromatophore cells.  This is known as the Turing Model, and has been explored repeatedly since the 1950s, notably by Jeremy Green in Developmental Biology in 2015. For more on the Turing Model click here.

Why are spots formed?

As discussed in my overview of pattern in nature, patterns are formed for a variety of reasons.  Some are used to protect from predation and camouflage.  Some are used to hide predators.  Some trick potential predators into avoiding an animal which resembles another species that has dangerous traits or an unpleasant flavour (Batesian mimicry).  Patterns can be used to attract mates or frighten off competition looking to steal your mates or territory.  So why do fish wear spots?  Below are some examples.

Wasp beetle showing Batesian mimicry.  It is harmless but resembles a wasp which puts off potential predators.

Trout and spots

The Brown trout Salmo trutta are covered in beautiful black and red spots, outlined in white.

Brown trout Salmo trutta

There are various reasons for this design.  The spots become brighter during mating which suggests they play a role in mate selection, and fish flash their colourful spots at potential competitors for females in lateral and frontal displays (Tim Travers 2014).

Close up of Brown trout pattern

They also help camouflage the fish, breaking up their outline from above and blending in with both reflected light and the speckled stones of shallow stream beds.

Brown trout swimming, seen from above

Tim Travers also suggests that the trout’s environment has led to the spots.  Evolving in crystal clear cold and glacial water, markings are visible to potential mates and rivals and therefore worth investing in.

Brown trout Salmo trutta sketch

Salmon and spots

Another spotted fish is the Salmon, Salmo salar.

Life cycle of the Salmon

Compared to similar fish in the Salmo family, such as Brown or Sea trout, the Salmon is relatively clear of spots.  However, they appear on the youngest fish, the parr, as red dots on the flanks and black dots on the back and dorsal fin.

Salmon parr

The next life stage, the smolt, has less spots, only a few on the back and gill cover.

Salmon smolt

The final stage sees the adult female hen salmon with lots of dark spots, and the male, in breeding colours, sporting red and brown and black dots.

Hen salmon

Male, or cock salmon also develop spots at mating time.  These are a complex network of red and black dots, overlaid on other blotches of colour.  Some anglers call the pattern a “tartan” because of its complexity.

Cock salmon

For more on the lifecycle of salmon look at my earlier blog or the Atlantic Salmon Trust’s page.

Salmon spots on wild vs farmed fish

There’s interesting research that suggests farmed salmon are up to 7 times more spotty than wild salmon.  As these patterns are laid down during the early smolting stage and are stable throughout a lifetime, seeing how spotty a river fish is can be used to figure out whether it is wild or an escaped animals (How does a salmon get its spots 2018 Jorgenson, Solberg and Glover).  The same consistency of pattern allows researches to identify individual fish, and could lead to less invasive and stressful forms of research on wild populations (FishBio 2018).

Puffer fish and spots

Pufferfish and box fish are often covered in little spots.  I could not find research pointing to what function these markings serve, they could be for communication, warning, mate choice, but are probably not a form of camouflage.  Perhaps it relates to the toxicity of some species and their ability to puff up by inhaling water if attacked?

Starry puffer Arothron stellatus

Sometimes these can be concentric circles of colour. In Diffusiophoresis-enhanced Turing patterns 2023, Benjamin Alessio explains how these spots are formed.  Based on the Turning model, diffusiophoresis shows how moving molecules bring other nearby molecules along with them.  If these molecules are colour-producing chromatophores, you  get different areas of colour.  This research was done on the Ornate box fish, a close relative of the puffer fish.

Turbot

Turbot are another spotted fish.  They are members of the flat fish family and have replaced their scales with skin and bony bumps called tubercles.  Turbot are able to change colour, literally changing their spots.  The skin has chromatophores producing black, red and yellow pigment.  Although these cells are in the same position, they can be turned on and off, allowing the fish to change colour in a matter of minutes or in some species, seconds.

Juvenile Turbot turbot Scophthalmus maximus 

They are also remarkable in that their bodies twist as they develop, meaning the adult has one eye which has migrated 90 degrees around its body.  This allows the fish to be incredibly flat.  Adult fish flap to stir up sand, and once a sprinkling of this lies on top of the spotted fish, it is indistinguishable from the sandy bottom of the sea floor.  Turbot spots make this fish a master of camouflage.

Adult turbot Scophthalmus maximus

For more on flatfish camouflage, have a look at Changeable Camouflage: How well can flounder resemble the colour and spatial scale of substrates in their natural habitats? by D. Akkaynak et al 2017 in Royal Society Open Science.

Sketch of the Plaice Pleuronectes platessa another colour-changing flatfish species

Leopard shark spots

The Leopard shark is also known as the Zebra shark because it has stripes when it is young.  These morph into spots as the shark ages.  It is thought that these different stages allow the markings to fufill different functions.

When young, the stripes break up the outline of the baby shark.  Lots of striped sharks together are confusing for a predator meaning it is less likely to fix on one individual animal.  This is known as the Predator dilution effect.  The markings could also send a message to territorial fish, informing them that a baby shark is in no way a threat and therefore is not worth fighting.  It could even be a form of Batesian mimicry as the stripes resemble those on venomous sea snakes. (The Sandy Zebra Shark: A new colour morph in Copeia by Dahl 2019)

Zebra or Leopard shark Stegostoma tigrinum

The shark undergoes ontogenetic change before adulthood.  This means a change in appearance which is genetically linked to the age of the animal.  The adult shark emerges with distinctive spots.  Because this change occurs at sexual maturity, it’s been suggested that the spots may be involved in mate choice and breeding. (A Zebra that changes its spots by Sophie Maycock 2020).

Conclusion

This is the very tip of the iceberg when considering spotted fish.  Stingrays, Zebrafish, Triggerfish, Grouper, Guppies, Cichlid, and Surgeonfish can all be covered in dots.  It is much easier to find out what a fish with spots looks like than it is to untangle why it wears this livery.  Whether monotone or multicoloured, single spots or concentric rings and circles, one thing is certain.  The patterns on fish are stunning, and a real joy to illustrate and research.

For a whole lot more on colouration in fish, read Price et al’s overview in Pigments Patterns and Fish Behaviour in Zebrafish 2015.

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How are spots formed?

Spots in plants are caused by areas of darker pigmentation, usually red anthocyanins.  Plants sometimes have paler spots on their leaves which are caused by an absence of chlorophyll and are discussed in my blog on Variegation.  This blog will focus on a few species with spots as I could never hope to cover all the spotted plants in one blog (or one lifetime!).  The spots seen on fungi relate to their anatomy rather than the chemistry of their colour.

Orchids

Many orchids have dark spots on their lowest petal, the labellum.  The labellum is the landing pad for potential pollinators and its shape plus these markings attract insects.  Most orchids are pollinated by beetles and hymenoptera.  These insects assume they will access nectar produced at the labellum base and in the spur behind the flower, but in many cases Dactylorhiza orchids are food-deceptive, luring the pollinators in (and being pollinated) without giving them a nectar reward. (First Nature)

Diagram showing the position of the labellum

Orchids: Early Marsh Orchid

One orchid that does this is the Early Marsh Orchid Dactylorhiza incarnata ssp coccinea.  Each flower has a pattern of spots on the labellum, guiding the potential pollinators to the pollen-producing heart of the flower.

Early Marsh Orchid Dactylorhiza incarnata ssp coccinea

Plants growing in areas with less nectar-producing neighbours, such as heaths and bogs, do better with their trickery than those surrounded by flowering plants who deliver on their visual advertising. (Dactylorhiza incarnata and deceptive pollination by Lammi and Kuitunnen 1995 in Oecologia)

Orchid flower of Early marsh orchid Dactylorhiza incarnata ssp coccinea

Orchids: Common spotted orchid Dactylorhiza fuchsii

The Common spotted-orchid appears early in the year and not only has spotted flowers but also spotted leaves.  These are not always present, in plants with paler flowers these are less likely to appear.  There is variation in the leaves, both in the intensity of the colour and the number and shape of the spots.  In some plants, there will be a paler area within each spot, giving the plant a leopard-like appearance.  The spots are created by the purple anthocyanin which may also flush the stems and leaf tips red.  The spots run cross-ways to the longitudinal veins.

Common spotted orchid Dactylorhiza fuchsii

Heath spotted orchid Dactylorhiza maculata and Southern Marsh Orchid Dactylorhiza praetermissa are closely related and may also have spotty leaves and flowers.

Heath spotted orchid Dactylorhiza maculata

Orchids: Bee orchid

It would be hard to find a spottier orchid than the Cycnoches guttulatum.  This epiphytic plant attracts the Orchid bee Euglossa cybelia and glues its pollen-filled pollinium onto the insect, ensuring cross pollination with other plants of the same species.

Orchid bee Euglossa cybelia with Cycnoches guttulatum orchid

Perforated St Johns wort Hypericum perforatum

St. John’s wort is also spotted, but this is not to do with pollination.  The little “holes” that pepper the leaves of this plant are glands which contain a cocktail of hypericin and other chemicals.  These are thought to dissuade insects from eating the leaves.

The flowers also have spots, or little dots.  These are black, and appear of the edges of the petals.  You can also see them on the calyx edges, and they appear in many Hypericum species.

Slend St. John’s wort Hypericum pulchrum

Foxglove Digitalis purpurea

Nectar guides appear on flowers to guide pollinators to the centre of the flower.  Many are invisible to us as they operate within the spectrum of light that bees and butterflies use, which includes UV light.  You can see these if you shine a UV torch on open flowers at night.  However, some flowers have spotty nectar guides that are easy for us to see.   One example of this is the Monkeyflower Mimulus bolanderi, another is the Foxglove.

Foxglove Digitalis purpurea

Nectar guides radiate outward from the nectar reward and the high contrast also helps attract potential pollinators.  Foxglove are interesting as they have a guard system to help keep out insects who would like to take their nectar but would be unable to carry pollen and help in pollination.  At the throat of each flower there are a few stiff bristles which prove no problem to bees and bumble-bees but deter smaller insects.  In fact, the hairs might help bees scramble into the flower.

Flower of the Foxglove showing the nectar-guide spots

Another way foxglove select their pollinator is by having the nectar reward at the very base of the flower.  This means only long-tongued bumblebees such as the Garden bumble bee Bombus hortorum can access it.  However, some bees bypass the security system by chewing holes in the base of the flower and stealing the nectar.  For more on Foxglove pollination, check out Ray Cannon’s blog.

Foxglove Digitalis purpurea flower with White tailed bumble bee Bombus leucorum

Research proves that nectar guides are important.  When covered up, the scent and shape of flowers still attracted pollinators.  But there was a significant reduction in the percentage of those who inserted their proboscis to access nectar and then to pollinate the flower. (Dennis Hansen 2011 Proceedings of the Royal Society B: Floral Signposts)

Lamiaceae: Skullcap

The Lamiaceae or nettle and mint family also have clear spotty nectar guides on their lower petals.  This can be seen clearly in the Skullcap Scutellaria galericulata.

Skullcap Scutellaria galericulata

In cross section, you can see the position of the pollen-laden anthers, directly above the spotted landing pad on the lower corolla lip.  In many of these flowers, the weight of the visiting insect will cause the flower to rock forward and deposit pollen on its back.  (For a more detailed look at the mechanics of these levers take a look at Floral Construction and Pollination Biology in Lamiaceae by Claßen-Bockhoff in the Annals of Botany 2007)

Cross section of Skullcap Scutellaria galericulata

Lamiaceae flowers are pollinated by bees 66% of the time; but ants, hawkmoth, flies, and butterflies also play a part. (Shrishail Kulloli in Nectar guides in Lamiaceae, Current Science 2011).

Lamiaceae: White deadnettle Lamium album

The White dead nettle also has small spots on its lower corolla lip.  In this case they’re green dots against white.

White dead nettle flowers Lamium album

White dead nettle also attract pollinators with scent, oil, lipids and polyphenols. (Lamium album and nectar guides by Aneta Sulborska-Rozycka et al 2023 in Micron).

Fungi: Fly agaric Amanita muscaria

It feels wrong to put a fungus in at the end of a blog about flowers as they are a whole other kingdom.  However, one HAS to include the Fly agaric in a blog on spots.

Fly agaric Fly agaric Amanita muscaria

The distinctive white spots on the cap of this iconic fungus do not seem to have any purpose, or not that I found literature on.  They are remnants of the universal veil, a white sheath that covers the fungus’ fruiting body as it grows from the ground.  The toadstool breaks through the sac, and small warts of white tissue remain.  These may wash off in the rain.

Fly agaric Amanita muscaria cap

Fly agaric are poisonous and packed full of hallucinogenic chemicals.  However, the red colouration doesn’t seem to suggest toxicity in fungus.  The Ox tongue fungus Fistulina hepatica and Crimson waxcap Hydrocybe punicea are both red and edible (the latter is rare so please don’t eat it).

It is interesting that such a stark colouration on a toxic fungus seems to have no link to warning colouration.  Such a pattern on a beetle, fish, or butterfly would probably be a warning of toxicity.

Completed illustration of Fly agaric with materials

Conclusion

This whistle-stop tour of spotted plants and fungi has shown that the most common reason for spots on plants it as a nectar guide for pollinators.  However, some spots are glands and others, such as the warts of Fly agaric, appear by chance.

Whatever their purpose, the spots that we find on plants and fungus are both stunning and a treat to illustrate.

The post Spotted Plants and Fungi appeared first on Lizzie Harper.

I love geraniums, and am especially fond of the variegated leaves some types have with their circles of cream, green, and red. I think a geranium like this one is my favourite house plants which shows leaf variegation.

Ninety percent of all wild geraniums come from South Africa, and they’re hardy plants (although frost can kill them). There are loads of different types available from garden centres, and those whose leaves are striped with white and red areas are called Zonal geraniums (or Pelargoniums).  However, it’s tricky to tell geraniums and pelargoniums apart, as this blog from NZ Stuff explains.

This step by step blog follows on from my blogs on pattern.

Geranium and pelaronium sketchbook study

When I was researching why some plants have warning colouration, I found that flower petals of these Zonal geraniums paralyze the Japanese beetle Popillia japonica, a common garden pest in the US.  They do this by by mimicking insect neurotransmitters.  Thinking back to my blog on stripes, perhaps our striped leaf is a form of warning colouration?

On with the illustration.  The plant used in this step by step is Geranium “Mrs. Pollock”.

Choosing and Drawing a leaf

When you choose your plant, make sure it’s one with plenty of leaves, and with distinct markings that you can illustrate.  It might help to take the leaf off the plant so you can examine it better.

First step is to draw up the leaf in pencil.  Begin by drawing a rough suggestion of the leaf shape, and use the leaf veins as guides.

Rough outline of Pelargonium leaf

Work into the line drawing, looking for the shapes of each leaf lobe, and for the wide teeth on the leaf edge.  Plot in the lines where the red anthocyanin pigment first appears, and where the green pigment area ends.  A quick sketch so you don’t lose track of what colours go where can be helpful, and can be rubbed out later.

Look closer at the veins and draw the side veins.  You’ll be leaving these as white for a while, so feel free to give them a touch of thickness by using two pencil lines instead of one if it helps.

Detailed pencil drawing of Pelargonium leaf

Variegation: Adding greens

Now mix up a soft green. Daniel Smith Spring green, Cobalt blue, and a touch of Naples yellow works well.  Using little brush marks and looking at the leaf, start painting in the darker areas of green.  Look for patterns in the way the shadows fall.  Having a good strong light helps with this, a daylight lamp behind the left shoulder works wonders.  There are deeper greens down where the radial veins meet, and on the right hand of the central vein.  It’s a bit darker on the underside of the branching veins.  Let the paint dry.

Deep greens are added to the leaf

Make a tint of your green by diluting it with clean water.  Lay this on top of the painting, making sure to leave the veins as thin unpainted areas.  Leave paler areas in the middle of each leaf section, but try to blend the green in with the little brush marks. Ideally, it’s an easy visual transition between the pale and darker green.  Don’t worry about your pencil lines, you can rub them out later.

Main greens are completed

Variegation: Adding Cream

Mix a pale yellow. Naples yellow plus a dash of Pale cadmium yellow is the right sort of thing.  Keeping it dilute, pick out the edges of the leaf and the same shadows cast by the veins as before.  This area of leaf isn’t white, despite having no green cholorphyll.  Background pigments like carotenoids and flavonoids give that creamy colour.  Again, be sure to leave the white of the paper for your highlights.

Cream margins are added

Blend these areas of cream into the rest of the leaf margin with a tint of your yellow mix.  Once that’s dry, mix up more of your pale yellow and paint it over the entire leaf, including the veins.  Let it dry.  Using light pencil, you can draw in outside edges of the red, if you’ve not already done so.  It’s easier to see what’s going on now there’s some colour down.

Geranium leaf plus pencil guide to red areas

Variegation: Adding reds

Time for the red anthocyanin pigments.  This is a tricky colour to mix; it’s somehow crimson and bright orange-red at the same time.

We also have to be incredibly careful not to allow the addition of the red on top of the green to make a muddy mess, so go carefully.  Try mixing Alizarin crimson, Opera rose, and Cadmium orange.  Keep experimenting with your mix til it matches the reds on the leaf.

Starting on the inside edge of the red pigments, use tiny outward-pointing brush strokes.  Before these fully dry, go over them with a slightly paler, wetter red.  Be super careful not to let the red get muddy. Pull this scarlet out over the variegated pale margin, making sure it’s paler than the crimson you first applied. Let this dry and very carefully outline the vein edges in red.  Your leaf may well look a bit rubbish at this stage, but don’t panic.

Geranium leaf plus reds

Variegation: Adding shadow

Mix up a darker green, perhaps by adding purple to your existing green mix.  Pop a watery tint on this on top of the whole green area, including over the red areas.  Be careful not to mix the red and the green.  Let it dry fully.

Using a green darkened with blue or purple, pick out your darkest areas of green leaf.  The base of the leaf and right hand side of the central vein are darker, and there are tiny darker areas by the other veins.

Look for darker regions at the creamy edge.  With a delicate touch, pick these out with a mix of your pale yellow and a dash of green.  Using this to clarify the leaf edges helps pull the illustration into focus.

Once it’s dry, use a soft eraser to rub out the pencil lines.  Some watercolour papers handle this better than others, you can be quite vigorous with Fluid 100 HP and not harm the painting.

Geranium leaf with shadows added

Conclusion

Illustrating different colours on one leaf is not impossible, and feels far more frightening than it turns out to be.  Variegated leaves are beautiful, and well worth further examination.  Once you’ve given this leaf a whirl, a whole load of new subjects become available, and many are houseplants that can be painted year round.  For more on leaf variegation, check out my blog.

The post Geranium Variegated Leaf Step by Step appeared first on Lizzie Harper.

One of the things in nature which is worth taking a really close look at is pattern.  Spots, stripes and splotches decorate loads of living things; from beetles to reef fish, snakes to zebras, orchids to sunflower seeds.

Peacock Pavo pair with male tail on display

They have always amazed and delighted me, and I’ve recently looked a little further into them.

Ladybird Coccinella septempunctata

What are patterns for?

Patterns serve lots of different functions in nature.  They can provide camouflage, which works for predators as well as for prey.  This is true for plants as well as animals (Plant Camouflague by Niu and Sun, 2018)

Nightjar Caprimulgus europaeus settled camoflauged on the ground

They can be vigorous warnings, advertising toxicity.  The Monarch butterfly is toxic thanks to the milkweed its caterpillars feed on, and its colouration ensures any predator foolish enough to try and eat it once would not repeat the experience!

Monarch Danaus plexippus butterfly

Patterns can be used to attract mates (just think of the shimmering tail of a peacock), to mimic poisonous animals, and to guide animals to food sources.  IN certain habitats, such as coral reefs, many of these tactics are used at the same time making for a panoply of patterns and colour.

Red sea coral reef scene showing patterned clown fish, star puffer fish, and squirrel fish

Pattern variety

There’s variety in the patterns, and plenty of overlap.  Lots of spots can merge together into a loose stripe, as with the toad below.

Even slugs can have spots, as this Green cellar slug Limacus maculatus shows.

Green cellar slug Limacus maculatus

Stripes on plants can widen into blotches. In plants, spots and stripes can fall under the umbrella term of “variegation”, pale markings on leaves where there’s no green pigment.  Some animals and plants sport stripes and spots, and one flower is even decorated with chequer-board markings!

Variegated Yellow Archangel Lamiatrum galeobdolon subsp argentum

Plants show a wide range of patterns on their leaves, stems, flowers, seeds, and fruit.  There’s always a reason behind the spots, stripes and splotches; not only how they come to be there, but why they exist and persist across the generations.

Pattern and latin names

Although many people freeze when shown a scientific or Latin name, they can be really helpful in giving clues about the organism you’re looking at.  When it comes to patterns, anything with “zonatus” or “versicolor” in its Latin name is likely to be striped.

Turkey tail fungus Trametes versicolor

Anything including the word “maculata” will be spotty (see the slug above, Limacus maculatus), and a plant whose name includes “variegatum” will almost certainly be (you guessed it) variegated.

Lords and ladies Arum maculatum

Conclusion

So whether its spots or stripes, blotches or chequerboards, patterns are everywhere in the natural world.  Used for attraction, protection, hunting, warning…the purpose is endless.  And the result is a world full of stunning, patterned organisms.

The post Patterns in Nature: A quick overview appeared first on Lizzie Harper.

Many of the patterns you see on plant leaves, especially on garden and house plants, are caused by variegation.

Variegated leaves have areas of paler yellow or white on them, and vary widely form species to species, and between individual plants.  Some variegated leaves even have dark red or scarlet areas. So what’s going on to cause these markings?

Variegated zonal geranium leaf Mrs Pollock

Variegation happens when cells in the leaves end up without plastid pigments, which normally provide the green chlorophyll we see in most leaves.  This occasionally occurs in the wild, and can be triggered by too much cell oxidization. Without the green chlorophyll masking them, we see other yellowish pigments, or just the white of a colour-less leaf.

Variegation in the wild

It’s pretty rare in the wild because leaves that aren’t full of chlorophyll can’t photosynthesize properly.  This means they can’t produce the sugars the plant needs to survive.

Wild cyclamen Cyclamen hederifolia, Lesser Celendine Ficaria verna, Lungowrt Pulmonaria officianalis and Milk thistles Silybum do show variegation.

Cyclamen hederifolia sketchbook study

Variegated patches might help protect leaves from UV rays, help in pollination and seed dispersal, and be used to keep a plant’s temperature stable (Thermal Benefits From White Variegation of Silybum marianum Leaves. Shelef, 2019)

Lungwort Pulmonaria officinalis

Variegated Houseplants

Variegated garden and house plants are much more common.  They originally come from cuttings of wild plants, and are propagated over the generations because of their pretty leaf markings.

Hosta showing variegated leaf on the right (from The Garden Forager by Adele Nozedar)

You can get variegated forms of tons of common plants; hollies with white leaf margins, big waxy hosta leaves striped white, Hebes edged with cream, Geraniums with rings of colour on their leaves, Periwinkles Vinca, Salvias, Yuccas showing sword like striped leaves, big leaved rubber trees Ficus, Peace lilies Spathiphyllum, Calathea with their white blotches, Chameleon plants Houittuynia with leaves flushed crimson…the list goes on and on.

Chameleon plant Houttunyia cordata

Often these variegated forms originate from wild plants that come from plants from across the globe, and get planted wherever gardener’s want them, and conditions allow them to grow.

Reverting to the wild

However, if you put them in shaded and nutrient-poor parts of your garden, they’ll often revert to having green leaves as they struggle to produce the energy they need.  If you try to grow variegated plants from seed they too will mostly revert to type.  Having big blotches on your leaves that can’t produce sugars is not efficient, so in most cases (and certainly in temperate climates where water loss and sun damage aren’t big issues) plants will avoid variegation unless conditions are so good they allow the luxury of having inefficient foliage.

Types of Variegation: Blister

There are different forms of variegation.  Some leaves will have blotchy white marks as a result of damage cause by mosaic viruses.  These tend not to be propagated or grown by gardeners.

Blister variegation happens when there are little air bubbles between the surface and the body of the leaf.  These look like white or silvery areas.  This is what causes the pretty spots on Begonia leaves, and the stipes of the Aluminium plant Pilea cadierei  Wild flowers with this variegation are few and far between; the spotty leaves of Lungwort, the variations on Cyclamen leaves, and the white areas on Milk thistle leaves (where these blisters follow the lines of the leaf veins) come to mind.

Begonia Begonia pearce

Why use Variegation?

Some researchers have suggested these blotches might be a form of mimicry, making the plant look like it had already been attacked by leaf-miners. Leaf miners looking to lay their eggs would avoid such a plant, so the trade off between not being eaten and not being able to produce sugars in the white blotches paid off. (Leaf variegation in Caladium steudneriifolium (Araceae): A case of mimicry?, Soltau 2009)

Another suggestion is that white spots, stripes and blotches could act as a warning to animals thinking of eating them.  Lots of cacti, Aloes, and Euphorbia have impressive spines and these markings. (Aposematic (Warning) Coloration in Plants Lev-Youdun 2009)

Prickly pear Opuntia ficus-indica

In hot climates, the white areas of variegated leaves may help handle the fierceness of the sun, and with water retention.  It’s no surprise houseplant cultivars come from these regions.

Types of Variegation: Pigmentary

Pigmentary variegation happens when a leaf has areas without chlorophyll; or with another, stronger pigment such as anthocyanic (which cause pink and purple colours).  The Coleus houseplant is a good example of this, bright green leaves blotched with pink areas, then a darker purple where the two pigments overlap.

Coleus and other red-flushed plants

In wild flowers, one of the commonest plants to show this effect is the clover.  Look closely at a Red clover leaf Trifolium pratense.  There are much paler areas on each leaf, like arrow-heads.  These are distinct and occur on most of the plant’s leaves.

Red clover Trifolium pratense

You can mostly tell if a leaf is variegated, or if the blotches are caused by a deficiency in some nutrient or mineral.  The edges of variegated areas are sharply defined, and an individual leaf will not re-gain its’ green-ness if you change the soil conditions.  It might start growing new leaves which aren’t variegated, but leaves which are variegated remain so through their life – the missing plastid pigments can’t re-grow.

Autumn leaf colour and Variegation: The same source at work

It’s worth remembering that this effect, the lack of green chlorophyll, is exactly the same as what happens in autumn.  Leaves are normally green, but chlorophyll is broken down by deciduous trees as the colder weather approaches. The risk of damage outweighs any benefit a tree may get from keeping hold of photosynthesizing green leaves through winter.

Sycamore leaf Acer pseudoplatanus

What’s left?  The other pigments, many of which have been there round.  Yellows remain, caused by carotenoids and flavonoids (including one, lutein, which is what makes egg yolks golden!).  Oranges caused by other Carotenoids like beta-carotene (which also give carrots their colour) also remain.

These do get broken down as winter comes, but far slower than the chlorophyll.  Around now, trees also start producing the reds of anthocyanin.  Surprisingly, even now no-one really knows why this red pigment appears so late on in leaves, some suggest it might be protective.

Conclusion

Although variegation in the wild is not unheard of, it’s unusual because of the biological cost.  This isn’t true for house plants, hence the amazing variety of leaf colour we see.

Understanding what causes variegation also helps us know more about the chemistry and botany of leaves, which (one hopes) will end up with us admiring then even more.

The post Variegation: Patterns on leaves appeared first on Lizzie Harper.

Stripes are seen across the animal and plant kingdoms.  Although the first stiped animals you think of may be zebra and tigers, there are lots of striped beetles, snakes, birds, and loads of stripy fish.

Stripes for Camouflague

Stripes are a brilliant way of providing camouflage.  They break up the edges of an organism, making it harder to see against the background.  A baby tapir, rootling in the scrub of a forest will be almost invisible as patches of sunlight and dark shadow fall on its’ back.  If you see one in a different environment its’ stripes seem startling.

Likewise, a large predator like a tiger appears invisible as its stripes mimic the vertical lights and darks of the grass it uses as cover before it attacks.

Sketch of Tiger Panthera tigris , the first striped animal many people will bring to mind

Stripes as Camouflage: Breaking up the edges

Stripes are common on coral reef fish, where they not only break up the fish’s outline but can also dazzle and confuse potential predators.  Couple striking stripes with the surprise of flashing a big eye-spot, as many Butterfly fish do, and predators won’t risk an attack.

Snakes are often prey, and species with long stripes on their body use these to confuse predators.  The stripes flicker as the snake whisks away, and escape occurs before the predator can figure out where the edges of its’ prey are.

Variable kingsnake Lampropeltis Mexicana thayeri

Stripes as warnings of toxicity

Animals use stripes to signal their toxicity and to warn off predators. The most iconic example is the skunk with tis clear black and white stripes, but unpalatable caterpillars, cone shells, and stinging insects like bees and wasps also use stripes as a warning.

White tailed bumble bee Bombus leucorum

If a predator does happen to take a bite out of these creatures, they may well become ill or get stung.  Next time they see that distinct pattern, they’ll avoid it.  It’s interesting that so many insects sporting warning stripes are yellow and black.

Common wasp Vespa vulgaris

Colorado potato beetles (and many other beetles) have clear stripes.  They’re avoided by birds as they taste bad, another example of stripes being a warning to predators.

Colorado potato beetle Leptinotarsa decemlineata

Stripes for Mimicry

Stripes are used by mimics, harmless animals that “dress up” like toxic ones in order to avoid being eaten.  This is known as Batesian mimicry.  There’s a harmless British beetle, the Wasp beetle Clytus arietis which not only has yellow and black stripes, but also moves and behaves like a wasp.

Wasp beetle Clytus arietis

Another mimic happens when nestlings of the Cinereous mourner bird Laniocera hypopyrra hatch.  They’re orange and have odd, adapted feathers.  They move their heads slowly from side to side, and this makes them look a whole lot like some rather toxic caterpillars that inhabit the same Amazonian jungle. (Morphological and Behavioral Evidence of Batesian Mimicry in Nestlings of a Lowland Amazonian Bird, Londono et al 2015)

One plant uses stripes to mimic the damage done by leaf-miners.  The Milk thistle Sibilum maritum has white stripes following the lines of its’ leaf veins, caused by variegation.  These give off a message that the leaves are infested with leaf miners, and the adult flies avoid laying their eggs there, put off by the “competition” already within the leaves (Aposematic (Warning) Coloration in Plants, Lev-Yadun 2009)

Milk thistle Silybum marianum

A surprising use of stripes is shown by zebra; it’s been shown that these iconic markings don’t confuse predators, but flummox biting horseflies who avoid landing on the stripy surfaces (and biting the zebra). (Benefits of Zebra stripes: Behaviour of tabanid flies around zebras and horses. Caro et al 2019)

Stripes on plants

But why do plants have stripes?  They’re not active predators, lurking in the undergrowth.  They’re not hapless prey, trying to camouflage themselves in the shadows.  Although there’s some suggestion that plants do use pattern as a warning, this tends to be spots rather than stripes.  There is one example of a plant that uses warning stripes.  In Israel the same Milk thistle Silybum marianum is banded with white stripes and the wider the stripes, the stronger the prickles. (Local loss of the zebra-like coloration supports the aposematic and other visual defense hypotheses in Silybum marianum. Lev-Yadum 2017)

But most plants don’t use stripes for camouflage or warning.  So why stripes?

Stripes on Plants: Nectar guides

Plants need to be pollinated.  What’s more, they need to advertise to pollinators that they need pollinating, and that they have a sugary reward of nectar for any insect willing to do the job.  A really effective way to do this it to have stripes literally pointing to the nectar source, like arrows.

Insects can see ultraviolet rays (which we cannot), and lots of flowers have stripes and colours that only show up in UV light.  Under UV light dandelions have bright “red” centres, attracting bees to the flower.

Dandelion Taxicum officinale

Evening primrose, Hibiscus, and some daisies have evolved blue halos which centre around the middle of the flower and are clearly visible to bees.  Some flowers have very clear stripes when looked at in “bee vision”, like the Meadow Cranesbill.  These are also pointing the way to nectar.  It’s no surprise that these stripes, coming out from the centre of a flower, are known as “nectar guides”.  For mroe on this check out the blog by the No dig Gardener)

Meadow cranesbill Geranium pratense

If you look really closely at most flowers, you may well see these nectar guides.  Sometimes they’re indistinct, and just look like a few dark lines near the centre of the flower; or as paler areas near the centre of the flower, emphasised with stripes.

Detail of Marsh violet Viola palustris showing nectar guides

Violets, cranesbills, pea and bean flowers, Mallow, lupins, and hibiscus are just a few flowers with these clear nectar guides.

Mallow Malvus sylvestris claerly showing nectar guides

Some flowers are striped all over, not just at their throats.  These stripes are often simply the veins of the petals picked out in another colour.  Wood sorrel, Cranberry hibiscus, and the bearded iris all show these markings.

Wood Sorrel Oxalis acetosella

Wider stripes and Flowers

Other flowers have wide stripes of different colours. These tend to be garden plants like Petunias, camelias and tulips, and these stripes are not common in the wild.  One exception is the Candy cane sorrel, Oxalis versicolor whose white petals are edged with a crimson stripe.

Tulip flower Tulipa Bestseller

Plant breeders select for them, and it’s important to remember that function and form get a bit confused once you start looking at human-bred organisms.

Orchids often have elaborate patterns, including stripes.  Unusually, Tiger orchids, Oncidium has stripes which go across its petals, rather than following the veins of the petal.  It makes for a dramatic flower!

Striped leaves

Leaves of houseplants often have white stripes (and other markings) along them.  This is a result of variegation, and is selected for by plant breeders.

Spiderplants Cholorphytum comosum are probably the most cultivated houseplant in the world.  In their native southern Africa, they have pain green leaves.  Other stripy house-plants include Calathea, Sanservia, Bromeliads and Croton.  Many of these are native to hot climates, and the stripes that do occur in the wild could relate to preserving water or reducing heat.

Illustration of ferns and striped Calthea leaves

The leaves of the Zebra plant Cryptanthus zonatus (the English and Latin name give us clues to what’s coming!) have white stripes running across them.  This is much less common than the longditudinal stripes, and is also a result of variegation.

Striped fruit

Fruit can be striped, especially those in the Cucurbitae family which includes melons, squashes, cucumbers and gourds.  These stripes can be quite distinct and variable, and a selection of gourds and melons would make a good still life.

Striped and (an unstriped) Cucumbers Cucumis sativus

Striped seeds

Some seeds are striped.  Sunflower seeds, cannabis seeds, and chickpeas can all be stripy and interestingly, all have non-striped versions too.  Striped sunflower seeds have thicker coats than monochrome black ones, although it’s unclear why this should be.

Conclusion

We live in a stripy world, for all sorts of reasons.  Next time you’re asked to think of a striped animal, consider all the creatures sporting stunning stripes who are not zebra or tigers!

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