Nature's Crayons

I promise this is the last post on plant pigments!  It's a short one, too.  I just want to take advantage of the last of the glorious fall colors. 

The first thing I noticed at the outdoor classroom this week is that the pond has turned brown.  The brown color is from tannins in the oak leaves that have fallen into the pond.  Our pond water has basically turned into oak tea.  The mosquitofish in the water don't seem to mind.  They are a very tolerant species.  High concentrations of tannins in water can alter the water chemistry, changing the types of organisms that can live in the water.  If we had fragile aquarium fish in our pond, we would want to change the water, but our organisms (fish and snails) are adapted to a wide variety of water conditions, including tannins.

Tannins from oak and maple leaves have turned the water brown.

The next thing I noticed at the classroom was leaves of every plant color you can think of.  See if you can name the pigments in the leaves from our classroom.  Here's a reminder of the plant pigments:

• Chlorophyll = green
• Tannins = brown
• Carotene = orange
• Xanthophyll = yellow
• Anthocyanins = red and purple

Xanthophyll in a maple leaf.

Tannins in a maple leaf.

Chlorophyll in magnolia leaves, xanthophyll in the leaf petioles.

Anthocyanins in sourwood leaves.

Chlorophyll and anthocyanins in oak leaf hydrangea leaves.

Anthocyanins, carotene and xanthophyll.

Anthocyanins, carotene and xanthophyll.

These pictures are just the tip of the iceberg.  When you walk through the outdoor classroom this week, see how many differently-colored leaves you can find.  Bring your fall Crayons if you like, and draw what you see.

Winter, Spring, Summer, Abscission

It's happening everywhere right now!  Plants are chopping off their own organs, and they are piling up in yards all over town!  How come no one is worried about this epidemic of leaf death??!!  Well, it happens every year, so I'm pretty sure the plants are going to recover.  Still, why on earth would plants get rid of their most important organs?  That's what we'll address in today's post.

Closeup of leaf abscission zone on sourwood.

In the picture above, you can see the color difference between the pale pink of a leaf petiole (technical term for a leaf stem), and the bright red of a sourwood twig.  The line between those two differently-colored plant parts is called the abscission (ab-SIZH-uhn) zone. 

Fresh leaf scar where the abscission zone dissolved and the leaf fell off.

This time of year, the layers of abscission zones are changing.  One layer is hardening and filling up with a corky substance called suberin.  Suberin is waterproof and heals what would otherwise be a wound where the leaf falls off.  The leaf scar in the picture above is dry and not losing sap because suberin has sealed the wound.  The second layer in the abscission zone is made of thin-walled, weak cells that self-dissolve when the plant is ready to shed its leaves.  Abscission zones are usually quite noticeable this time of year on any plant that is in the process of losing its leaves.  Take a look at the next two pictures and find the abscission zones.

Sourwood leaves and petioles (stems) about to undergo abscission.

The abscission zone is at the base of the leaf petiole where it attaches to the twig.

It is extremely unusual for living organisms to shed any part of themselves except for the production of offspring.  Some lizards have tails that fall off to distract predators, and many plants lose their leaves in the fall - but I can't think of other examples of falling-off body parts.  Of course, most organisms constantly rebuild their outer-coverings and some organisms can replace body parts that are bitten off, but voluntary amputation is strange, indeed! 

The loss of body parts comes at a huge cost.  Plants work all summer to catch enough sunlight to grow more leaves and get bigger, and leaf abscission every fall would seem to waste that energy.   But as with the lizards that lose their tails, there are also benefits.  Lizards' bodies escape to live another day and regrow another tail.  Plants benefit from shedding leaves by not having to maintain those leaves during the winter.  Leaves are tender tissues that would become disfigured and die when frozen.  Try putting some lettuce leaves in the freezer over night and then take them out to thaw.  You will notice they turn to mush when they return to room temperature.  In order for plants' leaves to survive winter, they would have to be tough, like holly, magnolia or spruce leaves, which take much more energy to produce.  Plants with leaves that survive freezing grow more slowly than ones that shed their leaves.

Dogwood with remnants of chlorophyll along veins and lots of anthocycanins (red pigment).

Plants have many ways to minimize the costs of losing their leaves.  They move all available nutrients out of their leaves and down into their roots to save the food for the next growing season.  Leaves fall near the plant that grew them and decompose, releasing their nutrients into the soil and further increasing the amount of nutrients recovered by the plant.  In this way, deciduous plants grow their own mulch.  Some plants, like walnut trees, even deposit compounds in their leaves that suppress the growth of competitor plants as the leaves decompose throughout the winter and spring. 

Rainbow of fall colors.

As leaves senesce (slow down and die) in the fall, they turn the variety of amazing colors we are so familiar with.  Plants' normal color is green, due to the most important compound in the world: chlorophyll.  Chlorophyll is the substance in plants that allows them to absorb sunlight and use the energy from sun to make food, a process called photosynthesis.  In the fall, chlorophyll breaks down, revealing other colorful substances plants use for photosynthesis: xanthophyll (ZAN-tho-fill), a yellow pigment, and carotene (CARE-oh-teen), an orange pigment.  As temperatures drop, some plants make anthocyanin (AN-tho-SIGH-uh-nin), a red pigment that helps the plants store sugars for winter.  Some plants reveal tanins (TAN-ins) in their leaves in the fall.  Tannins are brown in color and are thought to be waste molecules produced by plants.  They have a bitter flavor, though some tannins are pleasant, including the ones found in tea leaves.

Leaf scar on a buckeye showing scars where the leaf veins were sealed off with suberin.

So leaf abscission is a trade-off that works in parts of the world with four seasons.  Plants in the tropics and plants in colder regions keep their leaves.  Tropical plants don't have to deal with cold, so they don't shed their leaves unless there is a yearly dry season.  Plants nearer the poles of the planet don't have a long-enough growing season to start from scratch every year, so they have to grow slowly and produce evergreen leaves and needles.  We lucked out, and we get to see the beautiful fall colors that accompany leaf abscission.

Green Algae

The school where I work has an outdoor classroom that invites nature into our urban schoolyard and creates a peaceful outdoor space for students to learn about life.  We have trees, wildflowers, and a pond, each hosting their share of associated organisms.  I'll be doing some nature blogging about the outdoor classroom for use by teachers at our school, and I'm posting the first outdoor classroom blog post here:

Welcome!  I'm excited about starting an outdoor classroom blog.  I can't wait to see what we find in our little urban nature oasis.  The subject of our first post is green algae.

If you look under the surface of the pond, you see a very busy ecosystem indeed!  There are plants, fish and insects, and those are just the visible organisms.  There are way more microscopic organisms than big ones, which I'll save for a future post.

Green algae growing just below the surface of our pond.

The strangest macroscopic (big enough to see) organism is the filamentous green alga that forms clouds of soggy green cotton candy.  But what on earth are green algae?  They seem a lot like plants: they photosynthesize, they have cell walls, and they have chloroplasts (green structures that photosynthesize).  There are also some features of green algae that we don't usually associate with plants: they live entirely under water; they don't form roots, leaves or stems; and some of the microscopic ones can swim!  Scientists have wavered a bit about whether algae are actually plants or protists.  The discovery of how to sequence DNA has allowed algal geneticists to confidently classify green algae as plants, though the other colors of algae (red, brown and blue-green) are not classified as plants.  I have had to re-learn my green algae taxonomy!

Interconnected strands of green algae pulled up from under the surface.

Our green alga (alga, hard g, is singular, and algae, soft g, is plural) is a filamentous type, meaning it grows in long strands.  The filaments (strands) of green algae are only one-cell thick, which is surprising considering how tough they are.  Each algal cell is cylindrical like a soup can, and the filament is arranged like an infinite strand of soup cans glued end to end.

Green algae out of the water.

The color of green algae comes from the pigment chlorophyll, just like in other plants.  Chlorophyll is the molecule that can catch light to allow plants to use its energy to build food.  Green algae cells contain structures called chloroplasts that hold the chlorophyll plus all the other machinery needed to conduct photosynthesis.  All plants' cells contain chloroplasts.

I looked at the algae from our pond using a microscope that magnified what I saw by a factor of 100.  In the picture below, you can see the cell wall between adjacent algal cells, just above the pointer.  Cell walls are rigid structures made of cellulose (a strong, rigid molecule), and they give plant cells their shape.  Paper is made by starting with plant material and getting rid of everything but the cellulose, meaning that paper is essentially squished, dried plant cell walls.

The pointer rests on a filament of green algae.  A broken alga releases its cell contents. 100x

Another interesting thing in the picture above is the broken cell.  A chloroplast is slipping out of the broken plant cell in the center of the picture.

Below is another view under the microscope, with one normal filament and one filament with shrunken cell contents.  The chloroplasts and other structures have been compressed into a central structure in each cell.  The strange filament may be undergoing reproduction or it could be stressed, but either way, you can see the beautiful cylindrical shape of each individual cell.

Shrunken cell contents in the lower filament allow you to see the cell walls.  The round object is an air bubble. 100x

In our pond, the algae seem to be growing quickly.  There is ample sun for food, plus decomposing leaves and insect/fish excrement providing nutrients, the equivalents of vitamins in our food.  When you see a pond with lots of algae in it, you can assume that there are a lot of nutrients in the water, either from natural sources or from pollution.

Why Do Sunflowers Follow the Sun?

Blooming sunflower.

It feels good to look at, doesn't it?  Something about bright yellow and radial symmetry is so pleasing to the eyes and mind.  Perhaps the visual buzz we get from gazing on sunflowers is due to the arrangement of the flower parts in what is known as Fibbonaci spirals, which I will not attempt to explain to you, but which you can learn about here in a fascinating animation.  No matter how much you understand Fibbonaci spirals, sunflowers are captivating.

The top picture shows a recently-opened sunflower inflorescence, or group of flowers.  Each dot in the face of the sunflower is actually a single flower, and the picture above shows sunflowers at the stage of pollination.  After pollen has been transported from the male parts of the flower to the female parts of the flower, the female parts of the flower begin to grow into what we know of as sunflower seeds.  In the two photographs below, you can see a mature sunflower inflorescence transitioning to sunflower seeds.

Sunflower finishing blooming and turning to seed.

Sunflower seeds not yet turned black arranged in a Fibbonaci spiral, allowing for maximum packing of seeds.

Above, you can see whitish green sunflower seeds packed together with their pointy end in.   The Fibbonaci spiral arrangement allows the plant to pack as many seeds as possible into the space available.  As this sunflower matures, the seeds will turn striped white and black like what we're accustomed to seeing in the grocery store or birdfeeder.  For a more detailed description of sunflower floral structures, see my older post on aster-type flowers, written when I wrote catchier though less-internet-searchable titles for my posts.

Sunflowers also do that amazing sun-following trick that makes these plants seem to possess some mystical powers.  Well, if you'd like to maintain your sunflower mysticism, I suggest you skip the rest of the text in this post and just look at the pretty pictures.

Sunflowers facing the sun.

What's really going on here is something called heliotropism, and lots of plants do it.  Heliotropism means moving toward the sun.  If you've ever repositioned yourself periodically during an afternoon of misguided youthful tanning in order to get even sun exposure on all parts of your previously cancer-free skin, you've done heliotropism yourself.  The puzzle with sunflowers is, why do the flowers need to face the sun?  To even out tan lines? To look good in a white dress?  To appear thinner?  To fit in with their friends?  Read on.

The truth is, the stems of all actively growing sunflower parts - flowers and leaves - grow to face the sun in order to maximize photosynthesis.  During the day, the stems elongate on the side away from the sun, tilting leaves and immature flowers toward the sun throughout the day and ending up facing west at sunset.  When there's no light (so...night time), the other side of the stem grows, pushing the leaves and flowers back to the east where they will be facing the sun at sunrise.  Growing leaves and immature flowers are green and actively photosynthesizing, and heliotropism provides them with 10-15% more sunlight than just sitting still.

Take a look at the picture below.  On the right, you can see an immature sunflower inflorescence covered in green bracts, which are obviously photosynthesizing since they are filled with chlorophyll and appear green.  The younger sunflower has immature leaves held up and facing the sun as well.  The lower leaves on the younger sunflower, as well as all parts on the older sunflower, have matured, and though they are generally facing up, they are not facing the sun.  The older sunflower is drooping from the weight of the developing seeds.

Young sunflower parts following the sun, old sunflower parts stuck in place.

So just-opened sunflowers like the gorgeous ones in the vase below (if they weren't cut off from their stalks) are still growing some, so they still face the sun.  As soon as they mature, they usually end up facing east and staying there.

Bouquet of sunflowers

Gettin' Twiggy With It

A trip to the Chicago Botanic Garden this morning provided me with much blog fodder for this and the next few posts.  Spring is early this year, bringing a bounty of beautiful sights to the Botanic Garden. 

Greenish yellow weeping willows and orange willow shrubs on the left side.

Many trees and shrubs have responded to the spring weather, even if they haven't leafed out yet, by becoming quite colorful.  Their twigs have begun to manufacture photosynthetic pigments near the surface of the bark, making for yellow, orange, red and green twigs.  Forget everything you ever learned about plants - they photosynthesize using bark! (OK, don't forget anything, but you can add on.)  The picture above shows a lovely spring scene with willow trees and shrubs revealing their spring pigments.

Crimson tipped shrub willows.

The brilliant colors of the shrub willows drew me in for a closer look.  Up close, they have yellow stems with bright red tips.  The greenish yellow of the lower stems is probably a mix of chlorophylls and xanthophylls (here is an explanation of pigments in this earlier post).  The red is likely due to anthocyanins, but there is almost certainly chlorophyll also present in the twigs masked by the stronger red pigments.

Willow twigs with crimson tips.

Red is a common pigment 'choice' for plants that are active in cold weather.  The red may act to filter out some excess light and act as a sunscreen for the plant.  Plants can't photosynthesize as quickly when it's cold out, and too much light can overload the slow system.  Red pigments also tend to absorb more heat than other pigments, and even a tiny increase in temperature can increase the rate of photosynthesis.  In this crimson-tipped willow, the narrow tips would be especially likely to freeze, so red pigments there could help them be more active in the cold.  Alternatively, since this plant is growing in a botanic garden, it is likely the product of selective breeding for aesthetically pleasing but physiologically useless traits - so the colorful twigs could just be pretty and not useful at all.

Red dogwood twigs.

Above you can see entirely red twigs of a shrubby type of dogwood.  I can attest that many types of dogwood twigs are often red in the wild as well as in botanic gardens.  People and nature seem to favor red twigs for winter growth.  The overall effect (below) of these red twigs is startlingly beautiful.

Dogwood shrubs.

Many plants opt for green chlorophyll for winter twigs, as seen this variety of rose-related shrub below.  These stems can actively photosynthesize any time the temperature and light are favorable.  The tough, thick stems are able to survive freezing where leaves cannot.  When the temperatures rise to predictably non-freezing levels, these roses will leaf out and photosynthesize in earnest for the growing season.

Rose stems.

When we came to Chicago in October, forecasts said it would be the worst winter ever.  Instead, it's been a record-breakingly warm winter.  Spring seems to be competing to outdo winter's numbers.  It's been 80 degrees for days now.  Plants that use temperature as a trigger to emerge from winter's dormancy are already leafing out.  Those that use day length as the gauge for the start of spring still look like they should for this time of year - leafless and grey.  I suspect the day-length strategy will work better this year, since Chicago has been known to have freezes into April.  Trees that leaf out early stand a good chance of having to grow new leaves after their first ones get frozen off.  Late leaf growth combined with twig pigmentation is a good strategy for climates with unpredictable spring temperatures.  Using twigs to photosynthesize can give a tree a good head-start on the growing season without the risk of having tender plant parts frozen off.

Fun With Flamingos

I get a little taste of home when I walk through the Lincoln Park Zoo on my walking route because the zoo has flamingos.  Unlike Tennessee flamingos, these ones actually move and are not made of plastic.  I noticed them in October when the weather was nice, and I kept seeing the birds on my walks as the fall progressed.  I assumed they kept the birds out because the winter has been so mild thus far.  Well, yesterday I walked the zoo in 20 degree weather with sleety ice forming crusts all over every surface, and the flamingos were still out by their pond!  I realized there must be a few things I don't know about flamingos, so I did some research.

Tropical Paradise

 The Lincoln Park Zoo's flamingos are Chilean flamingos.  These birds survive high in the mountains of Chile where the temperatures can get down to -22 degrees F at night.  When the weather gets that cold, they stay near hot springs so they don't freeze solid, but these guys can handle some serious cold even without hot springs.

Flamingo with black flight feathers

 Flamingos' reddish coloration comes from carotinoid pigments in the food they eat, which is mainly red algae.  They filter the red algae out of wetland water, and they can feed in fresh to salty water, unusual for a land creature since salinity is so difficult to deal with.  Adults grow longer and stronger flying feathers that are black in color, and the displaying flamingo in the picture above is showing off his fine but clipped black flight feathers.

One of these is a flamingo.

 Flamingos are not born with a curved beak.  While it looks like they have run into a brick wall, flamingos' beaks actually turn down naturally as they begin to feed independently.  The downward curve allows them to filter algae out of the water.  Baby flamingos have a straight beak for sucking crop juice from their parents' throats.  Crop juice is a liquid that is nutritionally similar to mammal milk.  Both male and female adult flamingos make crop juice to feed their babies.  It is produced in an organ that is an offshoot of their digestive tract, and the parents hork it up to feed their little ones.  I don't know what sounds less appetizing - milk from glorified sweat glands like we have or regurgitated milk.  The best part about flamingo milk: it's RED!

Posing for the camera.

 Flamingos have red 'knees', but their 'knees' are actually ankles.  From those red bulges in the photo above down to the ground is all foot.  I should say, the bones below the red bulges are homologous to the foot bones in all other vertebrates with feet.  They have the same number and arrangement of bones in their feet as we do, but some of their bones are longer, shorter or fused or vestigial to make a flamingo foot.  Flamingos have true knees also, but they are too high to see and covered by feathers.  When flamingo legs bend, it appears they bend the wrong way, but when you take into account that the major joint in their legs is the ankle, they are bending the way any ankle bends.

Grooming seems to be a major activity.

 The flamingos at our zoo spend a large amount of time grooming themselves.  It's fascinating to watch because it reveals the musculature they must have to control their feathers.  The birds can raise some or all of their feathers with muscles that attach to the base of the feather under their skin.  They can willingly control these muscles so their feathers puff up or lay flat on demand.  Humans have similar muscles that connect to each hair, but they are not voluntary.  You can feel the muscles contract when the hair stands up on the back of your neck or when you get goose bumps.

More grooming with fluffed up feathers.

Turnips

Turnips are ridiculously under-appreciated.  They are the easiest vegetable to grow.  They are marvelously delicious.  They produce anti-cancer compounds and their nutritional profile is similar to broccoli even though they look more like potatoes.  Their greens are the richest-tasting greens of all cooking greens.  To top it all off, they are in my favorite vegetable genus, Brassica.

The picture below is of an enormous purple turnip at the Chicago Botanic Garden, a fabulous botanic garden with an extensive fall vegetable section.  This turnip is pure white on the inside (I assume - I didn't cut it open), and it should also be white below the soil.  Sunlight causes the root epidermal cells to become pigmented in this variety of turnip.  The pigment seen here is an anthocyanin, but some turnips have a green suntan from chlorophyll production. 

A gigantic turnip!

The turnip in the portrait above, since it's very large and pigmented, is likely to have some zip to its flavor, much like a radish.  The greens will be piquant as well, like mustard greens.  The root would be delicious cooked in a stew with other vegetables, and the greens could be tamed by throwing out the first round of steaming or boiling water if necessary. 

My favorite turnips are Hakurei turnips, which are pure white regardless of sun exposure, smaller, and not hot.  They are sweet and fruity and even the greens can be eaten raw.  You can find them at farmers' markets in the fall and spring.  Their texture is divine when cooked - smooth and silky, and I like them sauteed or cooked into soups.  It's absurd to think of eating turnips without the greens in my book, so I always get the roots cooking while I prep the greens.  Then I cook the greens with the roots for the last few minutes for a great combination of flavors and textures.  YUM.

Turnip and greens, Brassica rapa.

 To grow turnips, just sow a thick line of seeds and cover them with a little soil.  As the turnips grow, you can thin the young plants by collecting some greens before the roots start to fill out.  In just a few weeks the turnip roots will grow and you can harvest them as you need them for several weeks.

Turnips and butterhead lettuce.

Turnips are members of the genus Brassica, which is a group of unassuming weedy-looking plants with fast growth rates and fantastic variation in growth forms.  Each brassica species modifies a different plant part to store energy, usually in response to humans breeding the plants to make agricultural varieties.  Turnips store energy in their roots (as do rutabagas), and the rest of the plant looks pretty normal.  Other brassicas put lots of energy into leaves (cabbage and kale), leaf stems (bok choi, seen below), flower buds and stems (broccoli and cauliflower), leaf buds (Brussels sprouts, seen below), stems (kohlrabi), and seeds (canola, mustard).  It's fascinating to me that these plants are so closely related with such striking similarities in leaf and flower structures but with such vast differences in other plant parts.

Brussels sprouts, Brassica oleracea var. gemmifera.

Bok choi, Brassica chinensis.

Brassicas generally are quite nutritious and low in calories.  Consuming these vegetables regularly appears to have a protective effect against many cancers, though the mechanism is not well understood.  For optimal amounts of the cancer-fighting compounds, eat these vegetables raw or lightly steamed, not cooked into oblivion.  Some brassicas contain bitter compounds detectable by a subset of the human population.  These people can't enjoy the wonderful flavors of brassicas because they find them to be too bitter.  Also, children are better at tasting bitter compounds than adults, which explains why they more commonly dislike vegetables. 

Pigment Pondering

No pictures today, which is ironic considering it's a post about plant pigments.  Think of it as an exercise for the imagination.  I promise pictures for next time, but today interesting fonts and colors will have to suffice to spice up the text. 

The previous post (which had lots of pictures), described the amazing plant pigment called betalain, found in Celosias and beets (and bougainvillias and cacti).  Very strangely, betalains have never been discovered in the same plant as today's pigment, anthocyanins.  Anthocyanins are the workhorse, common pigments, and betalains are the superhero pigments.  But anthocyanins are not without some amazing characteristics.  Come along and find out.

Anthocyanins are a group of molecules that are usually red, but sometimes they are blue, orange or even yellow.  They share a similar chemical structure and method of production in plants, and they are everywhere.  Every time you look at a plant and see red, unless you're angry or it's one of the plants with betalains mentioned above, you're looking at anthocyanins.  Red fruit, red leaves, red stems, and red flowers are all due to anthocyanins.

In plants, anthocyanins have many functions.  They can act as sunscreen, which is why immature leaves are often reddish.  Some trees' leaves produce anthocyanins in the fall to protect the dying leaves while their nutrients are recovered by the parent plants.  Anthocyanins are major antioxidants in plants, and they protect the plants' DNA from other types of radiation in addition to UV light.  Flowers use anthocyanins to attract pollinators.  Fruits use anthocyanins to attract dispersers.  Plants that grow amongst snow produce anthocyanins because they help the plant stay warmer and grow faster. 

Some anthocyanins change color with a change in pH.  The one in red cabbage turns red in acidic solution, blue at a neutral pH and greenish-yellow at a basic pH.  You can experiment with this at home with a red cabbage, some vinegar, some water and some baking soda.  The anthocyanins in some hydrangeas are red when the soil pH is around 6.5, and they are blue when the pH is a little lower, around 5.5.  The reason for the hydrangea color change has to do with the increased solubility of aluminum in very acidic soil.  The aluminum is used to make anthocyanins when it's present, which accounts for the blue color.  When aluminum is not available at a higher pH, the anthocyanins are made using iron.

All pigments are molecules that selectively reflect light.  Light coming from the sun, or from a light bulb, is white light, which contains light of all wavelengths.  Pigments absorb white light and hold on to most wavelengths, but a few specific wavelengths are bounced off the pigment.  Whatever those reflected wavelengths are are what your eyeballs detect when you look at the pigment.  Something that's red reflects light with only wavelengths of approximately 700 nanometers (very small).  Something that's violet reflects light with wavelengths of about 400 nanometers (even smaller).  Something that's white is not pigmented - it reflects all wavelengths.  Something that's black is also not considered a pigment - it reflects no light.  That's why looking at something that is black is like looking at a dark room - there is no light coming to your eyes from either.  Black clothes are hotter in the sun than white clothes because the black molecules in the clothes absorb all light that hits them.  The black molecules hold on to the light as heat.  And that is why I'll be wearing a white T-shirt tomorrow on the farm (and I'll bring my camera!).

In Which I Attempt to Fascinate You with a Minor Plant Pigment

The Amaranthaceae, or Amaranth Family, is a somewhat obscure plant family, but you'd never know it on the farm right now.  There are amaranth crops, escaped amaranth hybrids from last year, and native amaranth weeds taking over the farm this time of summer.  It's a colorful explosion of dramatic bloomers with other meek yet ubiquitous volunteers growing between the rows of actual crops.

The hoop house, a sort of open-sided green house, is bursting with ornamental cock's combs right now.  Cock's combs are in the genus Celosia, and they come in amazing colors: eye-searing red, blazing peach with yellow, glowing whitish-green and orange.  They are such shockingly bright colors due to the fact that they are fluorescent.  Fluorescent colors absorb light energy from outside the visible spectrum (like UV light) and then emit that UV light as visible light...so they do actually glow.  Fluorescence is most noticeable when visible lights are turned off and black lights are shined, but cock's combs are so fluorescent that you notice them in full sunlight.

Hoop house full of Celosias.

A Celosia close-up.  It's even brighter in real life.

Members of the Amaranthaceae and a few other closely-related plant families can fluoresce because they have an unusual class of plant pigments.  Most plants that have red parts use a plant pigment called anthocyanin.  Think maple leaves in the fall and apple skins.  The amaranths use a group of pigments called betalains for all their red and most of their yellow coloration.  Betalains are antioxidants, so they may have anti-cancer properties.  Betalains are also useful as dyes for food and cloth, but I doubt they are what make highlighter pens fluoresce. 

The fluorescence of cock's combs is useful for the plant - it attracts pollinators.  In the hoop house, the peach cock's combs were the hands-down favorite of bees and wasps.  Each plant was swarmed with pollinators large and small.  The peach sector of the hoop house was buzzing, audibly as well as visually, with insect activity.  Good thing I got over my giant ground hornet fear in the previous post. 

Peach Celosia, source.

Amaranths in the U.S. are herbs, though there are some tropical shrubs.  They have tiny flowers, usually clustered all together.  The flower parts are so tiny, they are best seen with a hand lens or dissecting microscope.  Other ornamental amaranths include Gomphrena and Iresine.  Edible amaranth, genus Amaranthus, is used as a grain.  It is an important high-protein cereal native to South America.  Weedy pigweeds, in the same genus as edible amaranth, are found here in the U. S., and though their seeds and leaves are edible, it is much more of a nuisance than a valued crop. 

On the farm, half of our interactions with amaranths involve planting and harvesting the Celosias and Gomphrenas and the other half are killing the pigweeds, spiny amaranths and escapees from last year's crops.  The escaped plants from last year are seeds that have fallen and overwintered in the soil.  They are usually crosses between different types of Celosias, so they have a blend of their parents' traits.  That means they might have unpredictable colors, small flower heads and irregular growth forms.  They don't usually make good cut flowers, and they have to be treated as regular weeds. 

An escaped and hybridized Celosia from last year's crop growing among the zinnias.

And here is your reward (or punishment, depending on your sensibilities) for reading to the end of the post:  Beets are in a closely-related plant family, the Chenopodiaceae, and their red pigment is also a type of betalain.  I have never really noticed fluorescence in beets, but I haven't tried them with a black light.  If you eat a lot of beets, you may have noticed one of the disconcerting properties of betalain.  Betalain is not readily digested by humans, and it either passes straight through the digestive tract or is absorbed into the blood and eventually filtered into the urine.  Either way, the betalains end up in the toilet bowl, the same color as when they were swallowed.