I’ve elected to treat this presentation as a parade, honoring the 1 January Rose Parade in Pasadena (with great sadness over current circumstances). There is, of course, a theme, which for this parade is “What’s the Big Idea?” Each idea we float comes with a sponsor, a Plant Family, setting the stage for February, when the presentation focuses on getting to know plant families.
Slides include a lot of written content, which from my perspective is not a good way to make a presentation. But I decided to include major points in the images so as to make this post more useful in refreshing your memory. So let the parade begin.
Our first idea, brought to you by the Lentibulariaceae (Butterworts and Bladderworts), emphasizes that plants are ALIVE. This becomes a critical issue in that “plant blindness” is a real phenomenon; many people don’t “see” plants as more than a backdrop, the surround of their lives. In some ways, living plants are given no more credence than plastic and artificial specimens we encounter in impossible settings (a cave-like bar) and even as stand-ins for the living (lawns in Las Vegas.)
Our sponsor panel showcases Utricularia inflata, the Floating Bladderwort, which makes a splash in still waters, particularly semi-shady borrow ditches along lumber roads in Pine forests, as well as a photo of a Utricularia colony in Camel Lake (Liberty County). The flower to the right is Pinguicula lutea, a spectacular Butterwort common along seepage zones.
The star-like rosette of a seedling Pinguicula pumila sounds lyrics of ‘Born Free’ as reminder that living beauty surrounds us, leading to a summary of what it means to be alive.
The bullet points describe life, but many subtleties do not make the list. One absolute is that cell sizes are limited. Yes, there are multi-nucleate cells of Valonia (a marine alga) large enough to hold in your hand, and people cite Ostrich eggs as the largest single cells. Additionally, each cotton “fiber” is a single-celled trichome formed in the epidermis of a cotton seed, and linen fibers are bast cells averaging 25 millimeters (an inch) in length. Generally, however, cells are much smaller, size is limited because organic reactions occur quickly and over incredibly short distances. Taiz et al (2018) highlight this point by describing diffusion rates. A molecule of glucose might diffuse the width of an average cell in 2.5 seconds, while calculations suggest 32 years are required for the same molecule to traverse a meter of water. Size matters.
The Mint family (Lamiaceae) sponsors our second floated idea, showcasing their zygomorphic (strongly bilaterally symmetrical), tubular flowers. The message here focuses on characteristics particular to plant cells that impact plant overall biologies and strategies.
The cell wall is a complex “fabric” extruded by each cell as microfibers spun out like an external cage, something like a cacoon. The webbing consists of cellulose macromolelcules, each made of 3,000 or more glucose units linked by a particular bond (1, 4 beta). Especially in woody plants, plant cell walls can thicken additionally, and are even impregnated with compounds that make them yet stronger (like lignin) or waterproof (like suberin). Cellulose is vaunted as the world’s most abundant macromolecule, with some specialists estimating this substance accounts for around 40% of accumulated biomass. It shouldn’t surprise you that cellulose has been vital to human civilization as a source of fiber, construction materials, tools, and even fuel.
The structure of cellulose was first determined by French chemist Anselme Payen in 1838, leading to its use in manufacturing celluloid, an early commercial plastic polymer. Realizing celluloid was manufactured by treating cellulose with nitric acid, and then dissolving the nitrocellulose in camphor might raise suspicion the polymer is highly flammable, a reality that proved fateful for early photographic films. But safer products would come along, such as cellophane, a polymer generated by dissolving cellulose in alkali (mercerization). Rayon, the first industrial textile fiber (called artificial silk), is made from cellulose and has been manufactured since 1894. Given the need for cellulose as a raw ingredient, it should be no surprise that the largest rayon manufacturer today has major production facilities in Mobile, Alabama.
Conferring rigidity to plant cells, cellulose walls allow very distinct biological and developmental strategies requiring internal water pressure (turgor) for leaves and herbaceous stems to remain fleshy and functional. A fallout of cell wall stiffness is the sessile lifestyle of plants; they don’t move around. No muscular tissue systems have evolved (though we find motor cells based on water movement and polysaccharide-based contractile cells), at least nothing like protein-based muscle, which would be useless given the limited flexibility of woody stems. Harnessed by their cellulosic straight jackets, we discover that when plant cells divide, there’s no pinching from the side as in animals cells, rather a pre-emptive plate forms early, setting a border wall between between the future daughter cells.
Many plant cells mature as functional units that are dead. Xylem tracheids and vessel elements harden up and hollow out, fibers achieve strength by thicking cell walls to the point of starving out their living core of cytoplasm.
Plants are not the only kinds of organisms that photosynthesize, but they are the most prominent in terrestrial landscapes, shaping our habits and creating our habitats. We use the term autotroph for “self-feeding” green plants, which applies to nearly all wildflowers. But nothing is absolute. Some of Florida’s wildflowers are saprophytes (obligately dependent on rotting materials), and a few are parasitic (like Dodder), taking carbohydrates and nutrition from other living plants. Many more are photosynthetic, but opportunistic (particularly in the Orobanchaceae) – tapping into roots of other plants to siphon off useful materials.
As “primary producers”, green plants feed and outfit humans and other animals. They are the foundation of the food web, with an astonishing capacity to colonize barren landscapes, bringing prospects of food, shelter, materials, and even altering soils.
With primary growth generated by meristematic tips, plants are linear and polar; growing tips know what’s up and what’s not, leaving a linear trail of compact cells to elongate and differentiate, guided by genetic instructions and environmental cues (see Big Ideas IX and X). Every aspect one associates with plants is the gift of special cells and tissues. Water flows through xylem cells and sugar solutions move through phloem tissue. Hardness relates to fibers, succulence comes with parenchyma, greenness means cells are photosynthetic, starchiness means cells are packed with amyloplasts. Essential oils, latexes, and secondary compounds form in specialized cells. Surface features such as plant hairs & scales (trichomes), root hairs, glandular cells (usually trichomes also), and guard cells (that create and manage stomata) form in epidermal tissues. Reproductive cells that begin as spores are generated by fertile tissues in anthers and ovules.
The Daisy family, or Composites, sponsor our third Big Idea, partly because many people interpret these as among the most recent (read “advanced”) flowering plants. The Asteraceae is certainly the largest family, but defining characters make it clear this is a solid evolutionary clade. You can know an Aster by its fruit, or by its heads.
In future presentations we’ll investigate family characters and terminology, but for the moment I need to explain that a standard term for the “head” of flowers that characterizes Composites is “capitulum”, and the fruit structure these flowers produce (a 1-seeded, indehiscent, inferior nutlet, or achene) is technically called a cypsela.
Perhaps one of the most astonishing conclusions of contemporary biological and evolutionary science is that cellular life (those life forms with membrane-bound nuclei) surviving today is practically singular in origin. Over three billion years ago, some ancestral cell co-opted other cellular forms adept at processing energy (mitochondria) and harvesting light (plastids). We think of those independent contractors as “endosymbionts”, or formerly free-living, specialized cells that were engulfed by some nucleus-bearing cell. Through incorporating those specialists, this super-cell acquired the mitochondrial capacity to process energy and chloroplast ability to generate glucose through light-harvesting, and thrived. That singular skill set persisted and succeeded, giving rise to the millions of kinds of nucleus-bearing organisms on earth today. You are welcome to disagree, but this understanding is baked into the concept of Eukaryota, the “Domain” that includes all animals, plants, fungi, seaweed, and many unicellular organisms. We interpret this Domain as a natural tree of life, branches of which trace their origin to a single ancestor. The shared genetic codes and biochemical processes confirm those relationships in absolute terms.
The many life forms we know today trace their metabolic existences though more than 3-billion years of continuous service. Each life that exists (every human, insect, wildflower, and buffalo) is a morsel of life everlasting, at least life that has endured more than 3 billion years.
Sarracenias have long been known for trapping insects that decompose to yield nitrogen-rich compounds available for intake. Recent studies suggest varying levels of engagement, with our local Sarracenia flava and Sarracenia rosea relying on breakdown by micro-organisms living in traps, while other Sarracenia species have been shown capable of exuding proteolytic enzymes (Koller-Peroutka et al, 2019), which appears to give those species added capacity to absorb larger molecules. These recent revelations remind us many mysteries of Florida’s amazing plants remain unresolved.
The first modern list of elements was published by Lavoisier in his 1789 Traité élémenaire de chemie (Elements of Chemistry in a New Systematic Order containing All the Modern Discoveries, English translation 1790), considered the first modern chemistry text. Lavoisier described elements as substances that could not be broken down further, but could be employed to generate all other compounds. His list of 33 elements included 22 you’ll find in a modern periodic table. The other 11 that made his list included light and materials such as charcoal and silex (ground stone). By 1869, Russian scientist Dmitri Mendeleev, using the 63 elements then known, was prescient in organizing that knowledge as a modern take on a Periodic Table and first statement of a Periodic Law, a formulation that actually predicted future discovery of elements clearly missing from the progression. Today we recognize 94 elements that occur naturally (including the ten unstable elements) and others we can generate for brief existence.
Plants utilize 19 core elements, which stand out in this edited version of the Periodic Table. A few slides ahead you’ll find a list that indicates the general roles these elements fill in plant biological reactions. Setting aside Carbon, Hydrogen, and Oxygen, Taiz et al (2018) sort the remainder into four Groups: 1. Nutrients that are part of carbon compounds (N, S), 2. Nutrients important in energy storage and structural integrity (P, Si, B), 3. Nutrients that remain in ionic form (K, Ca, Mg, Cl, Mn, Na), and 4. Nutrients involved in redox reactions (Fe, Zn, Cu, Ni, Mo). Note: Three others (Aluminum, Cobalt, and Selenium) have been isolated in some plant studies and may prove to be important for certain plants. But we also know Aluminum is toxic to most plants, competing with other metals such as Magnesium.
The following slide repeats information given in the first presentation, basically providing students a memory device to recall the 19 elements important to plants.
The slides above and below are duplicates, laying out crucial roles of various elements. However, in the second version I’ve color-coded information that adds two groupings. The blue text reminds us that Carbon, Hydrogen, and Oxygen are plundered from air and water, while the gold text segregates important nutrients included in standard fertilizers (the well-known N:P:K ratio). Those elements tend to be highly mobil and easily leached from soils.
A return slide from the previous presentation, the following chart simply reminds us that over 90% of a plant dry weight is carbohydrate (principally cellulose and starches). Note the next element in abundance (after Carbon, Oxygen, and Hydrogen) is Nitrogen, a component of all amino acids and therefore characteristic of proteins (which includes enzymes).
Big Idea V is co-sponsored by the Irises and Violets, families with personal stakes in our perception of the spectrum (i.e. the rainbow.) The genus Iris and its eponymous family Iridaceae borrow their name from iris, Latin for ‘rainbow.’ Viola has ownership here because Isaac Newton determined there are 7 hues in the spectrum, adding the color Violet to the extreme side of Blue. This, of course, gives us the ROYGBIV memory device, though like Pluto, many people are not convinced Indigo merits inclusion. My own thoughts are that Newton considered Green as the center of our visible spectrum, and felt we should recognize as many hues on the blue side as on the red. There’s something compelling about symmetry.
Today, of course we understand the visible spectrum is a narrow set of bands in a much broader, unseen spectrum of electromagnetic radiation ranging from gamma rays (at the shortest, most energetic end) to radio waves (longer, less energetic waves). In our visible spectrum, at the more energetic end, Violet gives way to Ultraviolet, then x-rays. At the less energetic extreme of visible light, wavelengths longer than Red are perceived as heat, termed Infrared, passing then to yet longer microwaves and radiowaves. Colors of the visible spectrum, so central to living organisms, are simply slithers in the spread of electromaganetic waves continually bombarding us, representing energy levels sufficient to drive organic reactions yet short of the power inherent in Ultraviolet and xRays, energy levels known to destroy organic molecules.
The presentation poses Isaac Newton’s explanation of the spectrum as a first secret, with the second secret related to the concept that plants are green because they harvest red and blue light waves more diligently than green. This underlies so much of our perception of the world. Our eyesight evolved in a green world, an energetic by-product of photosynthesis – the visible light that is reflected and transmitted once chlorophyll and its associated array of light-harnessing antenna pigments have harvested the blue and red wavelengths. Green, logically, is the color humans perceive best; we are told it’s possible to discern over a million shades of green. It is the backdrop to our lives, and the reason red stands out so naturally (artists call red the complement to green because the two colors do not share any adjacenct shades).
The slide above, recalled from the first presentation, focuses on the nature of sunlight vis a vis photosynthesis. A figure in the following slide graphs sunlight striking a given leaf area from the perspective of total sun energy delivered to earth, energy that made it through the atmosphere to the leaf, and energy captured in the leaf to drive photosynthesis. One way of interpreting this graph is to focus on the space between the two absorption peaks (the blue lines) for plants. Light under the red line and outside (above) the blue line is the visible light that passes through or reflects from foliage, therefore what we “see” when we look at plants. Thus light reflected or transmitted by a leaf is perceived as overwhelmingly green.
The next slide parses that same information from a different perspective. Of total solar energy striking a leaf, 50% is not absorbed, 15% is reflected or transmitted (mostly green), 10% results in heating, and 25% is metabolized. The result is that 5% of energy striking a leaf may be converted to carbohydrates (where it is chemically stored). Because heat is both useful and potentially detrimental, I include heat with metabolism from the same viewpoint as the CFO of a major corporation would hype the level of business by posting gross sales. That is, 35% of energy striking a leaf is taken in and used in some way. Subtracting the direct costs (heat, metabolism), the Net Profit is 5%, which is the standard income anticipated from most institutional endowments. You can look at photosynthesis as the Earth’s endowment, supporting all life.
The final set of slides explains that photosynthesis is not the only way plants interact with light. And pure sunlight is not the only “quality” of light plants use. Think of plant canopies as filters. Light transmitted to the ground level has been filtered, and is now richer in the green spectrum as compared to full sunlight. That means plants in the shade of canopies cope with strikingly different conditions. Shade-loving plants manage this deprivation naturally.
Plants that live both in full sun and in shaded areas may show differing growth forms, due not simply to lower energy levels of light, but potentially to the changed color balance. This will sometimes relate to the ways blue light and red light act as environmental cues. Red and far-Red light impact levels of phytochrome pigments, which have regulatory roles in controlling growth and flowering. Only recently, since 1993, have botanists identified blue light receptors and begun to appreciate regulatory roles for blue light, impacting activity such as stomatal opening and even flowering (Huq, Lin, & Quail, 2024). Much remains to be learned in these regards, but the lessons are clear: Plants not only harvest light for energy, but respond to light through many significant pathways that predict seasonal growth and flowering, fine-tune productivity, and regulate senescence.
The Pickerelweeds have been chosen to sponsor Idea VI due to their intimate relationship with fresh water. It’s a small family, represented in Florida by two (or three) genera with three species, including the native Pontederia cordata an elegant, tropical-seeming element of many watery edges. As behaved as P. cordata seems, its near relative, Water Hyacinth (variably listed as Pontederia crassipes or Eichornea), is an aggressive floating plant, native to South America and problematic in fresh waterways worldwide. Plants of all species appear to produce heterostylous flowers.
The figure above brings home a remarkable contradiction. Water is the most abundant liquid characterizing so much of the Earth’s surface, while it is relatively limited on a universal scale. The figure represents all of Earth’s water as a sphere hovering over Kansas. A much smaller sphere, mounted over Kentucky represents the volume of fresh water on the planet. The two spheres constitute the medium that makes life possible, reminding us that though seemingly everpresent, water is a precious resource.
The slide above lists many ways water serves plant life, while the statement below focuses on the simple fact that plants use more water than animals. It is the force that vitalizes and flows through them.
The next Big Idea to float past you relates to Plant Life Cycles. Before molecular biology became the dominant field in plant biology, descriptive botany was dedicated to Systematics, Anatomy, and Morphology. The Morphologists, working almost completely with visible features, made incredible gains in understanding plant biologies through painstakingly charting and comparing life cycles and structural homologies (same derived organs that may prove adapted to differing tasks). A consistent set of observations related to Plants (in fact to all life) established sequences we observe in sexual life cycles. Once Anatomists developed enough information concerning nuclear chromosomes, it became apparent that all organisms evidencing sexual reproduction pass through a stage in which cells have a single set of chromosomes and an alternating phase during which cells function with two sets. The single-set phase is termed “haploid” and the two-set phase is “diploid.” In studying Mosses and Ferns, we can identify two distinct, free-living plant bodies, a small flap of green tissue that is the haploid plant, called the Gametophyte (because this plant produces the sexual cells, the gametes) and a diploid phase called the Sporophyte (because this phase generates cells that undergo reductive division (meiosis) to produce spores, which grow into Gametophytes. Complex? Yes – Convoluted? No.
The rotate (round and radially symmetric, i.e. actinomorphic) flower of our favorite Rosegentian is here to chart this cycle for wildflowers. Details of this same story are related in the general notes, so we will just outline the most basic process here. A seed, which began development as a single, diploid cell called a zygote, matures and germinates. The seedling progresses through vegetative growth, a matter of days for some herbs and as much as 20 years for a White Oak, leading to development of flowers. Flowers will form anthers and carpels (ovaries), which we interpret as the male and female roles respectively. Anthers might be borne in the same flower as carpels, in separate flowers, or either on separate plants.
Regardless, the anthers produce spores that are haploid, each of which will grow into a tiny, non-green plant that is a pollen grain. This is the male Gametophyte, and each grain is armed with two sperm nuclei, ready to mate. In a carpel, an ovule forms, inside which a female spore (a megaspore) develops into a microscopic, totally imbedded and dependent haploid organism we consider the female Gametophyte. This “plant” generates an egg. Union of a sperm nucleus with the egg nucleus is “fertilization” and forms the zygote, which holds a set of chromosomes from the sperm and a set from the egg; the zygote, therefore, is the first diploid cell of a new generation. That’s it. The sperm cell and the egg cell did not “come to life” because they were living through the entire experience. From this perspective, the cell structure, cytoplasm, plastids, and chromosomes that make a Sabatia today have existed (and yes, they have experienced great change) for over 3 billion years.
The figure above illustrates a fern life cycle, which makes it easier to appreciate the reason Morphologists were able to imagine alternating generations. The diploid plant, the archetypal fern, produces specialized structures (sori) on leaves. We call this plant the sporophyte because the sori generate spores (which have a single set of chromosomes). Each spore, given the right circumstances, germinates and becomes a tiny independent plant (shown in the diagram as a green, heart-shaped plantlet) we call the Gametophyte, because this is the plant that will produce the gametes (i.e. the sperm and egg cells).
Given time and persistence, you can compare the fern life cycle to that of the un-named, imaginary flowering plant below (in a figure from Taiz, et al). I created an orange dotted surround to indicate which stages one should imagine as the gametophyte phases.
Below, the Sabatia flower volunteered to dress up as the wildflower life cycle, beginning with the stigma pointing toward fertilization and stepping around the phases in clockwise manner.
We talked earlier about nutrition, but rootage is not completely restricted to acquisition of water and nutrients from the soil. In this context, rootage refers to being stationary, staying put. Except for some exuberant growth forms: (1) a few floating examples, or (2) the capacity of stems to vine and conquer space, or (3) rhizomes and tillers that might move growing points some distances, and (4) the production of separable vegetative plantlets, an individual plant is fixed in place, sometimes described as sessile. That means a plant, to survive, must be competent to cope with regular changes, such as seasonal climate regimens, as well as episodic challenges – a new exposure or threat due to sudden or gradual changes in the habitat (growth or destruction of a canopy, climate change, invasion by competitors, change in grazing, spread of disease, etc.) In the notes, we discussed strategies plants may employ to survive change.
Change comes, however, and plants can’t relocate, or can they? The possibility to move on, or to expand territory is vested in each life cycle with production of seed. Dispersal of progeny is the crucial strategy afforded to plants, and almost every plant has its own system. Some dispersal mechanisms promote long-distance dispersal, others having more limited effect. But given a few hundred generations, which becomes easy when the scale is geologic time, plants have gotten around.
This emerges as a point many people fail to appreciate, a concern relevant to long-term survival of diverse plants species. Before the wholesale impact of modern settlement, industry, and equipment, there were no new serious impediments to the ways in which plants might disperse and establish in appropriate habitats. We have eliminated most native habitats with construction and agriculture however, and remaining native sites are now segregated as disjunct parcels. Moreover, change in climate, which is admittedly a normal trend, has accelerated alarmingly. Shifts in global temperature (warming) are documented through Earth’s history, but normally those changes occurred over millenia, not in the brief course of two centuries, and not in response to human activity. Moreover, radical climate shifts people cite as natural do not mean those changes would be desirable for human life today. A sudden global episode of volcanic activity, though natural, would also prove disastrous for native plants as well as cultivated crops, not even to mention human activity. Over a few hundred million years, plant biodiversity would recover. But humans might not be around long enough to celebrate that genesis. The means we have inherited (or assumed) the reins over climate change (natural or human-induced) and will be forced to accept responsibility to manage (as best as possible) global climate in the future. It isn’t plausible that several billion people with technical capabilities would sit around and watch as climate shifts to extremes that make Earth uninhabitable, regardless as to the cause.
Returning to the topic of seed dispersal, expanding population footprint and establishing new outposts is crucial to persistence of plant species, and to evolution of variability. There’s no rest for the weary. Persist or perish.
The sponsors for our Rooted theme, Orchids, are experts in getting around. Their tiny seed are so small as to take to the wind, or even hitch-hike in mud or debris with which they might be transported by wading or fur-bearing animals who frequent similar habitats. In Apalachicola National Forest, my observations lead to speculation that dispersal of Platanthera chapmanii (Chapman’s Orchid) benefits from timing of mowing along the main highway. For decades, the Forest Service has restricted mowing along AR 65 to a single width most of the year, allowing a broader swath to be cut in late fall. By then, seed of the luxurious and diverse wildflower flora along this corridor has matured and perennials have died down for the cool season. Something in this formula appears to support an expanding population of Platanthera chapmanii, which first established as a very restricted colony I observed in 1975, and today spreads along a full half-mile of the greenway, with additional newly established colonies showing over a 7 mile segment. This spread is crucial, since other populations I had observed in open woodland throughout the forest have dwindled, even disappeared with increased density of canopies and understory.
Establishment of a new orchid population is not easy. An orchis seed differs from most other plant seed in lacking a developed embryo and harboring insignificant reserves. Germination depends on the seed landing in a microhabitat where the right soil fungus can immediately establish a symbiotic connection. Advantages of light, highly portable seed are easily compromised by the challenges of establishment. But it works for Platanthera chapmanii, at least in the Panhandle region and in nearly extinct populations in the East Texas Big Thicket as well. Once established, plants appear to persist over several years, sending up one (sometimes two) new flowering stems each summer.
And it is at flowering that plants have their second opportunity for dispersal – not seed dispersal, but dispersal of genetic material through elaborate pollination mechanisms. This dispersal functions to maintain genetic variability within populations. Given capacities of the principal pollinators, Papilio butterflies, one might speculate a healthy distribution, even when populations are dispersed over several acres.
In orchids, and other plants that develop elaborate pollination mechanisms, the often highly specific relationships with pollinators can generate opportunties for speciation. Some variable structure or character (fragrance, color, etc.) or visitation by a newly acquired pollinator can, over generations, result in mechanisms that segregate subunits of a population such that a new form, with its own pollination system, might be isolated from reproducing with the main fold. This is one manner in which new species could emerge, an example of what has been called biological species.
The photographs below show floral structure (the column) of Platanthera chapmanii. In the second set of images, you can see a pollinium extracted from an anther sac, attached to a pine needle by its own sticky pad (the viscidium). Below that photo is an image of Papilio visiting a P. chapmanii inflorescence; the pollinia attach to the butterfly proboscis just as they did to the pine needle. Positioning of viscidia, location of the stigma, and length of the spur mean that Platanthera chapmanii has succeeded in establishing populations basically distinct from its near relatives (and putative parents) Plathantera cristata and Platanthera ciliaris.
The ninth Big Idea is sponsored by the Grass family (the Poaceae), selected due to imagery in Walt Whitman’s Leaves of Grass editions.
“The grass is phủed over by the light and shade of the trees, it yields to the feet to be trampled upon, yet it is always coming back” Song of Myself
“I believe a leaf of grass is no less than the journey-work of the stars” Song of Myself
In the first lesson on basic botany, we discussed primary plant growth from shoot and root tip meristems. Understanding this format is key to appreciating plant structure. The points above make it clear that stems act like stems, and roots act like roots. Regardless how they appear on the outside, it is the internal anatomy and regulating hormones that determine growth patterns. Generally, stem tips grow up and root tips grow down in response to gravity. It’s amazing, actually. But some stems grow out horizontally, neither down nor up. Perhaps they follow the soil surface, but at some point, they know to turn upward.
Grass tillers are keen in this regard. Bunching grasses send out very short tillers (rhizomes) that turn up very quickly, keeping growth tight, in a bunch. In Wiregrass (Aristida), growing tips remain close to the soil surface, while long, needle-like leaves ply upward and own the forest floor. With these clumping grasses, only the flowering stems stand tall. Others wander, like Seaoats (Uniola), sending out runners that conquer a bit of territory before turning upward to make vegetative culms that support inflorescences. And then there are the runaways, such as weedy Bamboos and Johnsongrass (Sorghum halepense) that can tiller great distances, making them potential nuisances.
Grasses aside, all plants are directional divas. Each bud, each leaf, every flower element, even future roots have an appointed place and time. The plan may change given circumstances, water availability, light intensity or quality, damage from insects or herbivores, intentional pruning or harvesting,etc….. But baked into each genome is a basic blueprint and the capacity to detect what’s up, what’s down, which side is next, where there are resources, and even what conditions the changing seasons will bring. Plants are programmed.
Plants are not only programmed, they operate through repeating segments that we call phytomers. The shape of a phytomer might be very different at differing stages of growth, and in vegetative versus flowering growth, but throughout the many repetitions, shoot growing tips make only stems and leaves (as node/internode segments) while root growing tips only make roots.
In particular circumstances, tissues will “dedifferentiate” and generate new root or shoot growing tips. We excuse these instances by calling them “adventitious” growth. They aren’t breaking the rules, rather demonstrating a wonderful power of certain plant cells called “totipotency” – the ability to back up and re-invent yourself, even turning into a growing point.
The Bromeliad family has been chosen as sponsor for our final Big Idea. These plants, considered relatives of grasses, sedges, rushes, and cattails, defy the norm for their Order. They produce flowers that are individually showy, their ovaries are inferior (unlike the superior ovaries of the other families), they are mostly natives to the New World tropics, and more than half of the species are epipytic. These are the free spirits of the Grass world.
Their presence reminds us that all of the planning and investment a parent makes will not assure the offspring reach an assumed potential. The stage is set, with furnishings and accoutrements, the script (a genotype codified for thousands of years and well-rehearsed) is unchanged. But you can’t count on the auditorium – the walls, ceiling, lighting, or audience. That environment, normally predictable, can vary. And the next generation, the offspring, have to improvise. Even identical twins may find different solutions when on stage. This is nurture. Nature is limiting, but nurture is defining.
In plants we speak of the genotype as though it is software – instructions coded in DNA and transcribed to molecules that make things happen. Under perfectly controlled circumstances the outcome might be predictable, but nothing is “perfect” in that sense. There are as many possibilities in how instructions are interpreted by an individual as there are changes in circumstance. The fallout, the way a given individual develops, is the phenotype. The range of possible outcomes is termed Phenotypic plasticity.
Plasticity is crucial as it plays out between individuals. But we begin to see the range of possibilities even within a single plant. The illustration above shows leaf samples I collected last year (2023) from individuals of four white-flowered native shrubs, Cyrilla, Cliftonia, Clethra, and Itea. You might argue that in a single plant, or branch, instructions would not prescribe differences between something wrote, like a simple leaf, but take a moment to compare leaves of a tree that developed in full sun as compared to shade leaves on the same tree. The shade leaves are predictably broader and thinner in texture. Environment has a real impact on plant growth.
Below is a more controlled set of examples, illustrating differences between plants grown in sun versus shade.
In 2020, Drew Hiatt and Luke Flory (University of Florida) published results of comparative studies they conducted with six native herbs that grow in the same habitats as the invasive grass, Imperata. Their goal was to determine the range of plasticity plants expressed under differing conditions, principally in full sunlight as compared to the shade of a forest.
Their results remind us location makes a difference. Below I cropped out their photos of Helianthus angustifolius (the pair on the left) and Coreopsis floridana (the pair on the right). Within each pair, the plant grown in full sun is on the left, and the shade-grown plant is on the right. Sun plants are typically more stout and compact as compared to the same plant grown under shade (which isn’t simply less light, but also light of differing “quality”.)
Below is a summary index to the Ten Big Ideas. I hope these overarching concepts bring more meaning to your study of Florida’s native wildflowers.
Citations:
Huq E, C. Lin, and PH Quail, 2024. Light signaling in plants-a selective history. Plant Physiol. 2024 Apr 30;195(1):213-231. doi: 10.1093/plphys/kiae110. PMID: 38431282; PMCID: PMC11060691. https://pmc.ncbi.nlm.nih.gov/articles/PMC11060691/
Koller-Peroutka, Marianne, Stefanie Krammer, Anselm Pavlik, Manfred Edlinger, Ingeborg Lang, and Wolfram Adlassnig, 2019. Endocytosis and Digestion in Carnivorous Pitcher Plants of the Family Sarraceniaceae, Plants 8:367-376 https://pmc.ncbi.nlm.nih.gov/articles/PMC6843295/
Dupont, Corentin, Bruno Butais, Jean-Marie Bessiere, Claire Vilement, Tom Hattermann, Doris Gomez, and Laurence Gaume, 2023. Volatile organic compounds influence prey composition in Sarracenia carnivorous plants, PLOS ONE (Public Library of Science) https://doi.org/10.1371/journal.pone.0277603
U.S. Forest Service Web Page, Fern Reproduction https://www.fs.usda.gov/wildflowers/beauty/ferns/reproduction.shtml
Link to this Page: https://botanyincontext.com/ten-big-ideas-annotated-slideshow/