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.

Botany in Popular Culture: The Sunset Tree by the Mountain Goats

My obsession with plants means that I see botany everywhere – in the music I listen to, the shows I watch, the books I read, whatever. Just a fleeting mention of something plant related in any type of media will catch my attention, no matter how ancillary it is to the major themes. And that is the impetus behind this series of posts about botany in popular culture. Well that and, believe it or not, I do enjoy many non-plant related things, and this gives me an excuse to write about those things on a plant-centric blog.

TheSunsetTreeFrontCover

The Mountain Goats are a folk rock band formed by John Darnielle in 1991. It could be said that John Darnielle is synonymous with the Mountain Goats, as Darnielle is the chief songwriter and at times has been the only member of the band. The Sunset Tree is the Mountain Goats ninth studio album and only the second album featuring songs that are primarily autobiographical. The album that preceded The Sunset Tree, entitled We Shall All Be Healed, was about Darnielle’s teenage years as a methamphetamine user. The Sunset Tree describes growing up with an abusive stepfather. Heavy topics are kind of the Mountain Goats’ thing.

Darnielle’s lyrics are highly poetic and often nebulous – the listener is left to fill in the gaps. Thus, the storytelling in The Sunset Tree isn’t always direct. However, the scene begins to unfold in the second track, “Broom People,” as Darnielle seems to be describing his childhood living conditions: “all sorts of junk in the unattached spare room,” “dishes in the kitchen sink,” “floor two foot high with newspapers,” “white carpet thick with pet hair.” He also sings of “friends who don’t have a clue; well meaning teachers,” and how he would “write down good reasons to freeze to death in [his] spiral ring notebook.”

“Dance Music” reveals more as Darnielle at 5 or 6 years old is getting “indications that there’s something wrong.” As he sits watching TV, his stepfather is yelling at his mom, then “launches a glass across the room, straight at her head, and [Darnielle] dashes upstairs to take cover.” He turns on his “little record player on the floor” and makes a discovery: “so this is what the volume knob is for.”

A similar scene unfolds in “Hast Thou Considered the Tetrapod,” only this time Darnielle is the victim. He arrives home to find his stepfather asleep, so he sneaks up to his room knowing that if he awakes his stepfather, “there will be hell to pay.” But he does wake up, and he bursts into Darnielle’s room to find him sitting with his headphones on oblivious. The beating begins, and Darnielle sings, “then I’m awake and I’m guarding my face / hoping you don’t break my stereo / because it’s the one thing that I couldn’t live without / and so I think about that and then I sorta black out.” Darnielle describes being “held under these smothering waves” by his stepfather’s “strong and thick-veined hand.” But he remains hopeful that eventually – “one of these days” – he will “wriggle up on dry land.”

That sense of hopefulness can be found throughout the album. In “This Year,” Darnielle is a 17 year old longing to break free. The chorus repeats resolutely: “I am gonna make it through this year if it kills me.” In “Up the Wolves,” he assures us, “there’s gonna come a day when you feel better / you’ll rise up free and easy on that day.”

But there is obviously some anger and frustration expressed as well. Later in “Up the Wolves,” Darnielle sings that he’s going to get himself in “fighting trim” and then makes a series of threats: “I’m gonna bribe the officials, I’m gonna kill all the judges, It’s gonna take you people years to recover from all of the damage.” The song “Lion’s teeth” is a revenge fantasy. Darnielle envisions “the king of the jungle asleep in his car,” and since “nobody in this house wants to own up to the truth,” he takes it upon himself to wrestle the beast. He reaches into the lion’s mouth, grabs onto “one long sharp tooth,” and holds on. The chaos that ensues makes him realize he is “gonna regret the day [he] was born,” but since there is no good way to end it, he is determined to “hold on for dear life.”

The mood lightens during the last two tracks of the album. They seem to be about forgiveness, understanding, and letting go. In “Pale Green Things,” Darnielle tells of hearing from his sister that their stepfather had died “at last, at last.” Upon hearing the news, one of the first memories Darnielle has is of he and his stepfather going to a racetrack to watch horses run. In one scene he recalls looking down at the cracked asphalt and “coming up through the cracks, pale green things.”

It’s a poignant ending to an album full of dark memories. It’s also fitting, as it adds to the bits of hope scattered throughout. Seeing plants push up through concrete or sprout up in detritus collected in gutters and corners of rooftops or even just up out of the dirt in the middle of summer when the ground is hot and bone dry, all of these moments are testaments to the tenacity of living things. Life can, rightfully so, be described as fleeting, short, and fragile – easily snuffed out and erased. But the struggle for life is also fierce, enduring, and relentless. Darnielle’s story is one example of that.

sedums in a hole 2

The “pale green things” that Darnielle saw also symbolize the struggles of the little guy, the underdog, the downtrodden – a tiny, fragile plant pushing its way past solid, suffocating asphalt. It’s a common theme in Darnielle’s music – his latest album is called Beat the Champ, for example. His song “Wild Sage” is also a sign of that ongoing theme.

I work with plants all day, and I am continually awed by them. Daily I am stopped in my tracks, practically forced by some plant to admire one or more of the fascinating features it displays. It doesn’t surprise me that Darnielle would use “pale green things” to express hope and resiliency. Every day I find some kind of hope in plants, that whatever tough thing we are going through, we can one day “wriggle up on dry land” – pale green things pushing up through asphalt, wild sage growing in the weeds.