Tiny Plants: Duckweeds

Obviously, a series about tiny plants must begin with duckweeds – a group of aquatic plants that holds records in a number of categories including smallest flowering plants, smallest vascular plants, and smallest fruits. They are so small, in fact, that they don’t even have true stems or leaves, but rather are composed of undifferentiated vegetative tissue known as a thallus. Some species have one or a few tiny rootlets; others form no roots at all. However, what they lack in their hyper-diminutive size, they make up for in their ability to form massive colonies, creating dense mats that can take up serious square footage in a pond or lake. Depending on the species present, a single square yard of a duckweed colony can contain hundreds of thousands of individual plants.

Five genera make up the duckweed subfamily (Lemnoideae): Spirodela, Lemna, Landoltia, Wolffia, and Wolffiella. This group used to be considered the family Lemnaceae, but has since been placed in Araceae – the arum family. While they are considered flowering plants, not all species of duckweeds produce flowers, and those that do, do so only rarely. They mainly reproduce asexually through a process called budding, in which growth occurs at the base of the thallus (or frond) and eventually splits off from the parent plant. This process happens fairly quickly, which is why duckweeds are able to create substantial colonies.

 

Duckweed mats form atop the still waters of lakes and ponds, but can also form in very slow moving rivers and streams. Their presence is an indicator of high levels of minerals and nutrients, which is why they are commonly seen in agricultural and industrial wastewater ponds. Nutrients are absorbed through the underside of the thallus, so the rootlets of duckweeds likely function more for stabilization than for nutrient uptake. As duckweed mats expand and grow dense, they shade the environments below them. John Eastman writes about this phenomenon in The Book of Swamp and Bog: “Thick blankets of duckweed can shade pond bottoms, preventing adequate photosynthesis and making life difficult or impossible for submersed plants and animals…however, this is often a problem of only intermittent duration.” One potential benefit of such dense mats is that they can kill off mosquito larvae. Eastman points out that for this to be the case, the duckweed may need to be accompanied by other surface dwelling plants in order to create dense enough shade.

duckweed 1

Duckweeds overwinter by forming turions, small buds that act as storage organs. Eastman explains the process:

These tiny, kidney-shaped buds detach and immediately sink to the bottom, where they remain all winter. In the spring, each turion expels a gas bubble, which causes it to rise to the surface, where it rapidly develops into a new duckweed thallus. Turion formation requires a combination of bright sunlight and high water temperature.

Duckweeds colonize new areas either by moving downstream (if they have that option) or by finding themselves attached to the fur, feathers, or feet of animals that unwittingly transport them. The common name, duckweed, is likely derived from the fact that it is a major source of food for waterfowl. It is high in protein and rich in nutrients, especially when you factor in all the tiny critters growing on and among it. Muskrats and beavers occasionally eat duckweeds as well. Despite losses from herbivory by these creatures, being made mobile by their moving bodies is a major boon.

A collection of various duckweed species - photo credit: wikimedia commons

A collection of various duckweed species – photo credit: wikimedia commons

Duckweeds are also consumed by various species of fish, which is why they are commonly used as a food source in aquaculture. Frogs and other amphibians as well as various aquatic insects and microinvertebrates also consume duckweeds. The diversity of small animals and protists that use duckweeds and the environments they help create is incredible. Eastman writes:

Duckweed mats host a large variety of small fauna that feed, lay eggs, or shelter amid the plants. Many of them secure themselves to the thallus rootlets or undersides, where they snare and capture passing food organisms or particles. Protozoans, rotifers, insect larvae, and crustaceans are often abundant.

Humans have also been known to eat duckweeds. Duckweed farming is not a simple procedure, but a highly nutritious food source is the result when it can be done. A simpler alternative is to use the harvest as animal feed. Duckweeds are also used in bioremediation and are being considered as a source of biofuel.

Depending on the species, an individual duckweed can vary in width from 10 millimeters to less than 1 millimeter. They truly are tiny wonders of the plant world, and it is worth getting down to their level for a closer look (hand lens recommended).

Additional Resources

Field Trip: Bruneau Dunes State Park

One of the aims of American Wetlands Month is to encourage people to get out and visit nearby wetlands. I accepted this challenge by visiting the small lakes and marshes of Bruneau Dunes State Park which is located about 20 miles south of Mountain Home, Idaho (or, 70 miles from my house).

The park is known for its enormous sand dunes, claiming the tallest single-structured sand dune in North America which measures about 470 feet. The dunes began forming about 15,000 years ago during the Bonneville Flood. After the flood receded, the dunes continued to grow due to their unique location – a basin in which strong winds approach from both the northwest and the southeast, carrying sand from the surrounding steppes and keeping the dunes in place.

Two small lakes and a marsh are found nestled among the dunes, and the Snake River flows just north of the park. Apart from the dunes and the wetlands, the park also includes desert and prairie habitats and is situated in an extensive conservation area called Morley Nelson Snake River Birds of Prey. If that’s not enough, Bruneau Dunes State Park is home to a public observatory, where visitors can view the night sky and learn more about the stars and our place in the universe.

A marshy entrance to Dunes Lake

A marshy entrance to Dunes Lake

Climbing the sand dunes (and, if you’re up for it, sledding down them) is understandably a popular activity at the park. I spent a decent amount of time on top of the dunes, partly because the view was great and because the mosquitoes seemed to be absent up there. Yes, when visiting a wetland, you are advised to carry mosquito repellent, otherwise the cloud of mosquitoes that will undoubtedly surround you will make for an unpleasant experience. They will also make it difficult to stand still long enough to take a decent picture.

On top of a small dune looking across lake to large dune.

On top of small dune looking across lake to large dune

On top of large dune looking across lake to small dune.

On top of large dune looking across lake to small dune

Traversing the spine of a brontosauras (aka sand dune).

Traversing the spine of a brontosaurus (a.k.a. sand dune)

On top of the sand dune looking down at the lake and marsh.

On top of sand dune looking down at the lake and marsh

The marshes and shores around the lakes were populated with numerous wetland plants, including swamp milkweed (Aesclepias incarnata), duckweed (Lemna minuta), cattails (Typha sp.), and various rushes, sedges, and grasses. Native shrubs were also present, however the dominant woody plants were (unfortunately) introduced species: Russian olive (Elaeagnus angustifolia) and saltcedar (Tamarix chinenesis).

An entrance to the marsh

An entrance to the marsh

Flowers of bullrush (Schoenoplectus sp.)

Flowers of bulrush (Schoenoplectus sp.)

Russian olive (Eleagnus angustifolia)

Russian olive (Elaeagnus angustifolia)

Saltcedar (Tamarix chinensis)

Saltcedar (Tamarix chinensis)

Despite being there to explore and celebrate the wetland, the plants in the adjacent area (which appeared to be growing in almost 100% sand) continued to draw me away. Some I recognized easily, while others I could only identify to genus or couldn’t identify at all. Some notable observations included low lupine (Lupinus pusillus), sand-dune penstemon (Penstemon acuminatus), pale evening primrose (Oenothera pallida), and species in the genera Astragalus, Erigeron, and Eriogonum. Two bunchgrasses were particularly common throughout the area: Indian ricegrass (Achnatherum hymenoides) and needle and thread grass (Hesperostipa comata).

All of these plants are worthy of being photographed; however, the wind makes that difficult to do. Idaho is a windy state, and an area composed of wind-formed sand dunes is particularly windy. Between swarms of mosquitoes and consistent wind, capturing decent photos was a challenge. Aside from those minor nuissances, I had a very enjoyable time and hope to visit again soon.

Phacelia (Phacelia hastata)

Silverleaf phacelia (Phacelia hastata)

Nakedstem sunray (Enceliopsis nudicaulis)

Nakedstem sunray (Enceliopsis nudicaulis)

Have you visited a wetland this month? Or do you plan to? Share your adventures in the comments section below.

Botany in Popular Culture: Saga of the Swamp Thing

From the swamps of Louisiana comes a fictional character that is entirely composed of vegetation, has the appearance of a monster, and the consciousness of a human. He is called the Swamp Thing. Created by Len Wien and Bernie Wrightson, the Swamp Thing made his first appearance in the ninety-second issue of House of Secrets in 1971. He was then given his own series, which after 19 issues was handed off to up and coming author, Alan Moore.

Moore was an established comic book writer in the United Kingdom, but this was his first time writing for an American imprint. The work Moore did on Swamp Thing left a lasting impact on the comic book industry and helped establish Moore as one of the greatest comic book writers of all time. While Moore wrote more than fifty issues of The Saga of the Swamp Thing, I am narrowing this post down to the first volume, which compiles issues 20 – 27.

SwampFix

When Moore inherited the character, the Swamp Thing was thought to be (and also thought himself to be) the vegetable form of Alec Holland, a scientist who blew himself up while experimenting with a bio-restorative formula he was developing. Because Moore had some plot lines to dispense of before he began his own telling of the story, it only made sense to have the Swamp Thing killed off in the first issue so that he could reveal who or what he really was.

The beginning of issue #21 finds Dr. Jason Woodrue examining the Swamp Thing’s corpse. Woodrue is a villian that goes by the name Floronic Man and is himself a plant-human hybrid. The men who killed the Swamp Thing got Woodrue out of jail so that he could help them do an autopsy. During the autopsy, Woodrue makes a startling discovery: “We thought that the Swamp Thing was Alec Holland, somehow transformed into a plant. It wasn’t. It was a plant that thought it was Alec Holland! A plant that was trying its level best to be Alec Holland.” In the explosion, Holland’s body was completely incinerated, but due to the help of the bio-restorative formula that followed Holland into the swamp, the swamp plants fashioned themselves into a new creature with the form of a man and the consciousness of Holland.

swamp thing 1

The bio-restorative formula is key because it allows the Swamp Thing to regenerate. Woodrue knows this and takes advantage of it. He moves the Swamp Thing’s resting body back to the swamp. Conveniently he finds Abby Cable there, one of the Swamp Thing’s good friends. Woodrue informs her that the Swamp Thing is not Alec Holland, news that is difficult for her to take. As the Swamp Thing awakens, he must also come to terms with the fact that he is not who he thought he was. Meanwhile, Woodrue/Floronic Man harvests and eats a tuberous growth protruding from the Swamp Thing, which enhances his powers to control plant life.

swamp thing 2

Floronic Man is upset with animal life, particularly humans for the collective destruction that they have caused plant life. He is determined to take revenge for the harm that has been done to “The Green.” He causes plants to grow up rapidly and consume buildings and cars and wrap around humans to kill them. Amidst his mayhem he explains his vision of “another green world, as there was at the beginning, before the beasts crawled up out of the oceans. Those long, green centuries where no bird sang, where no dog barked. Where there was no noise! Where there was no screaming meat!!”

The Justice League is called in, but there isn’t much they can do. This is a job for the Swamp Thing who, while wandering through the swamp coming to grips with his new identity, senses trouble in The Green. He then realizes that Floronic Man must be involved, at which point he arrives on the scene and gives Floronic Man a good beating and a stern talking to.

Floronic Man is obsessed with the idea of plants taking over and destroying all other life. He has clearly gone mad, threatening to make the plants “pour out oxygen” so that “all the animals will die.” He is convinced that only plants will remain and that “it’s the only way to save the planet from those creatures.” The Swamp Thing rhetorically asks, “And what will change the oxygen back into the gasses that we need to survive when the men and animals are dead?” That seems to shut Floronic Man up. Schooled by logic, he slowly loses control of the plant life he had recruited to do his dirty work, at which point the Justice League swoops in and picks him up. The Swamp Thing retreats back to the swamp, embracing his new identity – elated to be alive and feeling at home in the swamp.

The final three “chapters” of the book are focused more on Abby. The Swamp Thing is around, and he definitely shows up for some fight scenes, but Moore seems to be working on developing Abby’s character. After all, she and the Swamp Thing have a future together. In one fight scene, a demon rips the Swamp Thing’s arm off. At which point, the Swamp Thing nonchalantly picks up his arm, reattaches it, and resumes fighting the demon.

swamp thing 3

Throughout the book, Moore’s writing and storytelling is exceptional. A brief recap such as this cannot do the book justice. Moore’s prose must be read to be truly appreciated. The Swamp Thing is a fairly minor character in the comic book world, and one of the very few that brings botany to the forefront. Thanks to Moore and the artists that worked with him, Saga of the Swamp Thing gives this great character the exposure and legacy it deserves.

For more authoritative reviews, check out the following links:

Ethnobotany: Cattails

“If you ever eat cattails, be sure to cook them well, otherwise the fibers are tough and they take more chewing to get the starchy food from them than they are worth. However, they taste like potatoes after you have been eating them for a couple weeks, and to my way of thinking are extremely good.”  – Sam Gribley in My Side of the Mountain by Jean Craighead George

franz

Illustration by Franz Anthony (www.franzanth.com)

Ask anyone to list plants commonly found in American wetlands, and you can guarantee that cattails will make the list nearly every time. Cattails are widespread throughout the Northern Hemisphere. They are so successful, that it is hard to picture a wetland without them. In her book, Braiding Sweetgrass, Robin Wall Kimmerer discusses this well known association:

Cattails grow in nearly all types of wetlands, wherever there is adequate sun, plentiful nutrients, and soggy ground. Midway between land and water, freshwater marshes are among the most highly productive ecosystems on earth, rivaling the tropical rainforest. People valued the supermarket of the swamp for the cattails, but also as a rich source of fish and game. Fish spawn in the shallows; frogs and salamanders abound. Waterfowl nest here in the safety of the dense sward, and migratory birds seek out cattail marshes for sanctuary on their journeys.

The two most abundant species of cattails in North America are Typha latifolia (common cattail) and Typha angustifolia (narrow leaf cattail). T. angustifolia may have been introduced from Europe. The two species also hybridize to form Typha x glauca. There are about 30 species in the genus Typha, and they share the family Typhaceae with just one other genus. The common names for cattail are nearly as abundant as the plant itself: candlewick, water sausage, corn dog plant, cossack asparagus, reedmace, nailrod, cumbungi, etc., etc.

Cattails have long, upright, blade-like leaves. As they approach the base of the plant, the leaves wrap around each other to form a tight bundle with no apparent stem. As Kimmerer puts it, this arrangement enables the plants to “withstand wind and wave action” because “the collective is strong.” Flowers appear on a tall stalk that reaches up towards the tops of the leaves. The inflorescence is composed of hundreds of separate male and female flowers. Male flowers are produced at the top of the stalk and female flowers are found directly below them. In the spring, the male flowers dump pollen down onto the female flowers, and wind carries excess pollen to nearby plants, producing what looks like yellow smoke.

After pollination, the male flowers fade away, leaving the female flowers to mature into a seed head. Just like the flowers, the seeds are small and held tightly together, maintaining the familiar sausage shape. Each seed has a tuft of “hair” attached to it to aid in wind dispersal. In The Book of Swamp and Bog, John Eastman writes about the abundant seeds (“an estimated average of 220,000 seeds per spike”) of cattail: “A quick experiment, one that Thoreau delighted to perform, demonstrates how tightly the dry seeds are packed in the spike – pull out a small tuft and watch it immediately expand to fill your hand with a downy mass.”

cattails bunch

cattail fluff

Because cattails spread so readily via rhizomes, prolific airborne seeds mostly serve to colonize new sites, away from the thick mass of already established cattails. The ability to dominate vast expanses of shoreline gives cattails an invasive quality that often results in attempts at removal. Various human activities may be aiding their success. Regardless, they provide food and habitat to numerous species of insects, spiders, birds, and mammals. A cattail marsh may not be diverse plant-wise, but it is teeming with all sorts of other life.

Ethnobotanically speaking, it is hard to find many other species that have as many human uses as cattails. For starters, nearly every part of the plant is edible at some point during the year. The rhizomes can be consumed year-round but are best from fall to early spring. They can be roasted, boiled, grated, ground, or dried and milled into flour. Starch collected from pounding and boiling the rhizomes can be used as a thickener. In the spring, young shoots emerging from the rhizomes and the tender core of the leaf bundles can be eaten raw or cooked and taste similar to cucumber. Young flower stalks can be boiled and eaten like corn on the cob and taste similar to artichoke. Pollen, which is high in protein, can be mixed with flour and used to make pancakes and baked goods, among other things. The seeds can be ground into flour or pressed to produce cooking oil.

Cattail leaves can be used to make cords, mats, baskets, thatch, and many other things. Kimmerer writes about the excellent wigwam walls and sleeping mats that weaved cattail leaves make:

The cattails have made a suburb material for shelter in leaves that are long, water-repellent, and packed with closed-cell foam for insulation. … In dry weather, the leaves shrink apart from one another and let the breeze waft between them for ventilation. When the rains come, they swell and close the gap, making the [wall] waterproof. Cattails also make fine sleeping mats. The wax keeps away moisture from the ground and the aerenchyma provide cushioning and insulation.

The fluffy seeds make great tinder for starting fires, as well as excellent insulation and pillow and mattress stuffing. The dry flower stalks can be dipped in fat, lit on fire, and used as a torch. Native Americans used crushed rhizomes as a poultice to treat burns, cuts, sores, etc. A clear gel is found between the tightly bound leaves of cattail. Kimmerer writes, “The cattails make the gel as a defense against microbes and to keep the leaf bases moist when water levels drop.” The gel can be used like aloe vera gel to soothe sunburned skin.

Eastman rattles off a number of commercial uses for cattail: “Flour and cornstarch from rhizomes, ethyl alcohol from the fermented flour, burlap and caulking from rhizome fibers, adhesive from the stems, insulation from the downy spikes, oil from the seeds, rayon from cattail pulp, …” To conclude his section on cattails he writes, “With cattails present, one need not starve, freeze, remain untreated for injury, or want for playthings.”

Additional Resources:

Happy American Wetlands Month!

To kick off this year’s American Wetlands Month, I am reposting something I posted three years ago. I have updated the links and added a few more resources. In celebration, all Awkward Botany posts in May will have something to do with wetlands. An underlying goal of American Wetlands Month is to encourage people to get out and visit wetlands in their area and find out what they can do to help conserve them. Hopefully this series of posts helps to further that aim.

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“May is American Wetlands Month! No matter where you live, chances are there’s a wetland nearby that provides important environmental benefits to your community. Wetlands support diverse fish and wildlife species, filter pollutants from rain water runoff, help recharge groundwater supplies, prevent flooding and enhance property values.” – Earth Gauge (A program of the National Environmental Education Foundation)

Wetlands are ecosystems that are characterized by their vegetation (aquatic plants), their soils (formed during anaerobic conditions caused by being flooded or saturated with standing water), and, of course, their state of being largely saturated with water either seasonally or permanently. Examples of natural wetlands include bogs, fens, marshes, and swamps. Wetlands can also be constructed by humans for the purpose of collecting storm water runoff from urban areas in efforts to reduce the risk of flooding and avoid overwhelming municipal sewer systems during large rainstorms.

Wetlands are the most threatened type of ecosystem on earth, and we are losing them at a steady clip. Major threats to wetlands include land development, pollution (agricultural, commercial, residential, etc.), and the introduction of invasive species. Considering the benefits we receive from having wetlands around, it is imperative that we protect them. Earth Gauge offers some suggestions on how to do so.

wetland benefits

Speaking of wetlands, one of my favorite wetland plant species is marsh marigold (Caltha palustris). It is in the buttercup family (Ranunculaceae) and is common throughout the Northern Hemisphere. I became familiar with this plant when I was volunteering at a wetland in Edwardsville, IL. Perhaps you’ve seen it growing near you.

Marsh Marigold (Caltha palustris) - Photo taken at Idaho Botanical Garden.

Marsh Marigold (Caltha palustris) – Photo taken at Idaho Botanical Garden.

Additional Resources

What Is a Plant, and Why Should I Care? part two

“Organisms green with chlorophyll appeared pretty early in Earth history, diversified, and adapted to oceanic, coastal, and finally terrestrial environments. As this took place, the Earth turned green.” – Joseph E. Armstrong, How the Earth Turned Green

world turned green

The Earth not only turned green, but the composition of its atmosphere dramatically shifted. Thanks in part to photosynthesis, Earth’s atmosphere went from having virtually no free oxygen to being composed of about 21% oxygen. The increasing availability of oxygen helped facilitate the evolution of more and more diverse forms of life. Had photosynthesis (specifically oxygen-producing photosynthesis) never come about, the Earth would not be anything like it is today.

There are organisms in at least three taxonomic kingdoms that have the ability to photosynthesize: Bacteria, Protista, and Plantae. A book itself could be written about how photosynthesis developed and how it differs among organisms. The important thing to note in a discussion about plants is that the type of photosynthesis that occurs in cyanobacteria is the same type that occurs in the chloroplasts of plants and green algae. Additionally, pigments called chlorophyll are only found in cyanobacteria and the chloroplasts of plants and green algae. As Joseph Armstrong puts it in How the Earth Turned Green, “evidence strongly supports the hypothesis that chloroplasts were free-living photosynthetic bacteria that became cellular slaves within a host cell.”

In Part One, we established that green algae are closely related to plants, and that a subset of green algae colonized the land and evolved into modern day plants. Plants are green because of cyanobacteria via green algae; however, cyanobacteria are not plants, and green algae may or may not be plants depending on your preference. Classification is not nearly as important as determining evolutionary relationships.

So, again, what is a plant? K. J. Willis and J. C. McElwain offer this summary in their book, The Evolution of Plants: “Plants are relatively simple organisms with a common list of basic needs (water, carbon dioxide, nitrogen, magnesium, phosphorous, potassium, some trace elements, plus various biochemical pathways necessary for photosynthesis). This list has remained almost unchanged from the first land plants to the present.” In Part One, we also listed three major features that all plants have in common: multicellularity, cell walls that contain cellulose, and the ability to photosynthesize.

Photosynthesis is a big one, because it means that plants make their own food. They are autotrophs/self-feeders/ producers. This sets them apart from heterotrophs, organisms that consume other organisms in order to obtain energy and other essential nutrients. Plants are at the bottom of the food chain, providing energy and nutrients to all other organisms that either directly or indirectly consume them. In Armstrong’s words:

“Eating and being eaten is a fact of life, a process by which the light energy captured by green organisms is passed through a series of consumers, a food chain, before eventually being lost as heat, which dissipates. Everything else is recycled with the able assistance of decomposers, primarily fungi and microorganisms, heterotrophs who obtain their food from dead organisms or their metabolic wastes. A large part of ecology concerns such trophic or feeding interactions, the energy transfers that result, and the cycling of biogeochemicals, the elements of life.”

Their ability to photosynthesize, among other things, gives plants a prominent role in the world’s ecosystems. Much more will be said about that as we continue, but first there are a few other things about plants worth mentioning.

Plants exhibit modular growth. While animals generally produce all of their body parts early on in life and rarely reproduce new body parts in replacement of lost ones, plants can continue to reproduce and replace body parts. Even at maturity, plants maintain embryonic tissues, which allows them to regenerate body parts as needed. This is one reason why so many plants can be propagated asexually via stem, root, and/or leaf cuttings. Roots can be encouraged to grow from unlikely places, and a whole new plant can be produced as a result.

Plants are generally stationary. Rooted in place, they must obtain everything necessary for life, growth, and reproduction by accessing whatever resources are in their immediate vicinity. Roots search the soil for water and other nutrients, and leaves harvest sunlight and carbon dioxide to make sugars. Relationships are maintained with soil fungi to aid in the search for water and nutrients, but otherwise, plants are largely on their own. Since they cannot run or hide, they must stand and fend for themselves when insects and other herbivores come to devour them. They have adapted a variety of chemical and physical defenses to address this.

Despite being largely immobile during their juvenile and adult phases, plants can actually be incredibly mobile during their embryonic stage (or in other words, as seeds/spores/progules). Employing biotic and abiotic resources, seeds and spores can potentially move miles away from their parent plants, enjoying a freedom of movement they will never know again once they put their roots down.

It is estimated that the total number of plant species on the earth today is around 400,000. (For reference, see this BGCI page and this Kew Gardens page. See The Plant List for up to date plant species names.) The first land plants evolved around 450 million years ago. It wasn’t until around 160 million years ago that the first flowering plants appeared, yet about 90% of the plants in existence today fall within this group. How many tens of thousands of species of plants have existed on Earth throughout history? I don’t think we can say. So many have come and gone, while others have radiated into new species. Exploring life that currently exists on this planet is an enormous pursuit on its own; add to that the exploration of life that once existed, and your pursuits become endless.

Sticky purple geranium (Geranium viscosissimum) one species of around species of extant flowering plants.

Sticky purple geranium (Geranium viscosissimum) is just one of more than 350,000 species of extant flowering plants.

At the close of the first chapter of his book, Armstrong highlights eight major historical events that have brought us plants as we know them today: “the origin of life itself, the development of chlorophyll and photosynthesis, the advent of the eukaryotic (nucleated) cell, the development of multicellular organisms, the invasion of land, the development of vascular tissues, the development of seeds, and the development of flowers.”  Consider that a brief synopsis of all we have to cover as we continue to tell the story of plants.

What Is a Plant, and Why Should I Care? part one

I want to tell the story of plants. In order to do that, I suppose I will need to research the 4 billion year history of life on earth. And so I am. Apart from satiating my own curiosity, studying and telling the story of plants advances me towards my goal of creating a series of botany lesson themed posts. Botany 101 and beyond, if you will. An ambitious project, perhaps, but what else am I going to do with my time?

So what is a plant anyway? We all know plants when we see them, but have you ever tried to define them? They are living beings, but they are not animals. They are stationary – rooted in the ground, usually. Most of them are green, but not all of them. They photosynthesize, which means they use water, carbon dioxide collected from the atmosphere, and energy harvested from the sun to make food for themselves. No animal can do that (okay…a few sort of can). They reproduce sexually, but many can also reproduce asexually. They are incredibly diverse. Some grow hundreds of feet into the air. Some barely reach more than a few centimeters off the ground at maturity. They have discernible parts and pieces, but they can also lose parts and pieces and then grow them back. There aren’t many animals that can do that. They have been on this planet for hundreds of millions of years, colonizing land millions of years before animals. Plants helped pave the way, and if it weren’t for plants, animals may not have stood a chance.

I don’t mean to pick on animals, it’s just that for a long time, humans grouped living things into just two kingdoms: Plantae and Animalia. Stationary things that appeared to be rooted to the ground or some other surface were classified as plants. Green things that lived in the water were also considered plants. Thus, lichens, fungi, algae, and everything we consider to be a plant today were placed in kingdom Plantae. Everything else was placed in kingdom Animalia. This, of course, was before much was known about microorganisms.

Dichotomous classification was reconsidered as we learned more about the diversity of organisms in each kingdom, particularly as the theory of evolution came into play and microscopes allowed us to observe single celled organisms and chromosomes. Eventually, fungi was awarded its own kingdom, which includes lichens – organisms composed of both fungi and photosynthetic species but classified according to their fungal components. Most of the algae was placed in a kingdom called Protista, a hodgepodge group of unicellular and unicellular-colonial organisms, some of which are animal-like and some of which are plant-like. Two kingdoms were also formed for prokaryotic organisms (organisms with cells that lack membrane bound organelles): Bacteria and Archaea.

Illustration of one current itteration of kingdom classification system (illustration credit: wikimedia commons)

Taxonomic kingdoms as we currently consider them (illustration credit: wikimedia commons)

In short, the answer to what is a plant seems to be whatever organisms humans decide to put in kingdom Plantae. One problem with this answer is that some chose to include certain species of algae and others don’t. But why is that? It has to do with how plants evolved and became photosynthetic in the first place.

Microorganisms developed the ability to photosynthesize around 3.5 billion years ago; however, the photosynthetic process that plants use today appeared much later – around 2.7 billion years ago. It evolved in an organism called cyanobacteria – a prokaryote. Eukaryotic organisms were formed when one single cell organism was taken inside another single cell organism, a process known as symbiogenesis. In this case, cyanobacteria was taken up and the eukaryotic organisms known today as algae were formed. The incorporated cyanobacteria became known as chloroplasts.

Not all algae species went on to evolve into plants. A group known as green algae appears to be the most closely related to plants, and a certain subset of green algae colonized the land and evolved into modern day plants (also known as land plants). That is why some taxonomists choose to include green algae in the plant kingdom, excluding all other types of algae.

Common stonewort (Chara vulgaris, a species of green algae (photo credit: www.eol.org)

Common stonewort, Chara vulgaris, a species of green algae (photo credit: www.eol.org)

The term land plants refers to liverworts, hornworts, mosses, ferns, fern allies, gymnosperms, and flowering plants – or in other words, all vascular and non-vascular plants. Another all encompassing term for this large group of organisms is embryophytes (embryo-producing plants).

Still confused about what a plant is? Three main features can be attributed to all plants: 1. They are multicellular organisms. 2. Their cell structure includes a cell wall composed of cellulose 3. They are capable of photosynthesis. Many species of green algae are unicellular, which is an argument for leaving them out of kingdom Plantae. Certain parasitic plants like toothwort, dodder, and beech drops have lost all or most of their chlorophyll and no longer photosynthesize, but they are still plants.

Deciding what is and isn’t a plant ultimately comes down to evolutionary history and common ancestry. As Joseph Armstrong writes in his book, How the Earth Turned Green, “Our classifications of human artifacts are totally arbitrary, but to be useful scientifically our classification of life must accurately reflect groupings that resulted from real historical events, common ancestries.”

Obviously this is going to be a multi-part series, so I will have much more to tell you about plants in part two, etc. For now, this You Tube video offers a decent summary.