By Sue Kusch
Aside from the bean growing experiments in primary school and the occasional plant part identification ditto sheet, many of us have not had any formal botanical education in botany. This is remarkable given that plants are the foundation of life for all animals, providing habitat, food, and medicine. Nature should be the core foundation of our formal educational curricula.
Understanding botany – the scientific study of plants, including their physiology, structure, genetics, ecology, distribution, classification, and economic importance – is important to our success in our gardens and more importantly, invites us in to the world of nature and its relationships. This article offers a basic overview of botanical concepts as well as a few hands-on activities for all the learners in the family
All organisms experience a series of developmental changes throughout their lives. A plant’s life cycle includes the following processes: germination, growth, maturity, flower and seed production, and death. Humans can manipulate plants’ cycles by removing flowers (deadheading) so the plant will continue to flower, or extend their cycles by growing them in warmer temperatures.
Many of our favorite food plants like cilantro, basil, lettuce, and tomatoes have annual life cycles: they complete all of their processes in one year.
Plants with perennial life cycles live more than two years, mature over several years, and generally produce flowers and seeds each year of their lives. Perennials enter into a dormant stage during the winter months with non-woody vegetation dying back in autumn and returning in the spring.
Plants that complete their life cycles over two years are called biennials. They produce leaves and roots (which store food) in their first year, overwinter, and then develop a stem, flowers, and seed in the second year. Common mullein (Verbascum thapsus) is a well-known biennial. Parsley(Petroselinum crispum) is also biennial but we treat it like an annual and harvest the entire plant at the end of its first year.
Plant Anatomy – External Plant Structures
Humans have studied the anatomy and physiology of plants for thousands of years and continue to do so as we think more broadly about how plants survive, communicate, and adapt to their environments. We do have a solid understanding of how plants complete their life cycles and how their anatomy is perfectly designed to support their processes.
Plants’ leaves, stems, roots, flowers, fruits, and seeds are called plant organs. Each organ is an organized group of tissues that work together to perform a specific function.
Plant parts are categorized by their function: sexual reproductive parts produce seed and include flower buds, flowers, fruit, and seed. Roots, stems, branch buds, and leaves are responsible for water and nutrient uptake and growth. They are not involved in sexual reproduction but can be used in asexual forms of reproduction like cuttings and grafting.
Have you ever wondered why roots like ginger, turmeric, and ginseng offer such powerful medicine? A plant’s root system is buried in the dark, damp soil surrounded by millions of hungry grubs, fungi, and bacteria, and in order to survive, they had to adapt to co-exist with those organisms. Unable to physically escape, the roots developed an array of chemical weapons that inhibit and fight attacks from soil microorganisms. The root system of a plant is key to its vigor, size, and ability to adapt and respond to environmental stresses.
Roots also learned to play nicely with their shared communities and developed symbiotic (mutually beneficial) relationships with certain fungi, an association called mycorrhiza. Mycorrhizae (meaning fungus and root) aid a plant’s ability to absorb water and nutrients.
The primary functions of a root are to anchor the plant, support its stem, absorb water and nutrients from the soil, and to store food for future growth. In some cases, roots can also be used for propagation. Herb gardeners who moved an established valerian plant and left a small broken-off tip of its taproot in place were probably surprised to see a new valerian plant emerge the following spring.
There are two main root shapes: taproots are singular roots that grow down into the soil and have no or limited secondary branching. The edible part of the carrot is a taproot. Plants with taproots are good anchors in shifting soil and windy locations.
The more common system is a fibrous root, which consists of many-branched roots that grow laterally just beneath the soil surface. If you have tried to remove portions of your lawn you have experienced the strength of a fibrous root system! Plants with fibrous roots are effective at controlling soil erosion.
Both root systems produce root hairs that are delicate growths that help the root to take in water and nutrients. Those little hairs on your carrots? Root hairs.
The health of roots influences the health of a plant’s vegetative system. For most plants, roots feed in the top twelve inches of soil, though taproots can retrieve nutrients and water at deeper levels. Thirsty roots like those of willow will seek water and that’s why gardeners are advised to not plant willow near septic systems. Roots need both water and oxygen to grow but will suffocate in consistently wet soil. Well-drained loose soil is the ideal environment.
Gather some root systems by gently pulling them out of the ground (psst! AKA weeding). Spread the roots out on a table and with a magnifying glass, explore the root hairs and root tips. Let them sit for a few days and observe what happens to the roots.
Stems are the plumbing of a plant’s anatomy. They form a continuous pathway from the root, through the stem, and ending at the leaves. This system contains two tubes: the xylem is responsible for moving water and dissolved minerals, and the phloem moves food in the form of sugars throughout the plant to keep it healthy. The other main function of the stem is to support leaves, buds, flowers, and fruits.
While we may think that stems only grow up from a plant’s root, science has revealed that what we may often view as roots are actually stems. Stolons are creeping horizontal stems or runners that grow at the soil’s surface; the spearmint in your garden uses stolons to take over. Rhizomes are horizontal stems that grow underground from plant to plant and ginger is a classic example. Is a potato tuber a root or stem? It’s a stem and those eyes are actually the stem’s nodes. And the most interesting stems are what most of us call bulbs: onions, tulips, and daffodils are actually shortened, compressed underground stems. Plants are full of surprises!
Dandelions have hollow stems so they make great bubble blowers.
- Find a tall dandelion and pick it from the bottom of the stem.
- Cut the flower off and make a second cut at the bottom of the stem (avoid squeezing the stem).
- Rinse the dandelion stem under running water to clean out any remaining white milky latex.
- In a small bowl, mix 1 T. of dish soap with ¼ cup water.
- Dip one end of the stem to stir the soap and water and to coat the stem end.
- Bring the non-soapy end up to the mouth and blow gently and wait for a bubble to form. Repeat.
Plant’s Plumbing System
To see how water and nutrients move through plant tissue, do the following experiment.
Gather three cut white flowers. Morning glories, carnations, mums or daisies or a stalk of celery with leaves can also be used.
- Make clean cuts on the bottom of each stem.
- Fill several small glasses with water and add 5-10 drops of food coloring.
- Place a flower in each glass and let sit overnight.
- Check in the morning for flowers that have changed color.
Extension: To make this more scientific, fill jars with differing amounts of food coloring (eg. 1 drop, 5 drops, and 10 drops) and predict the results.
Leaves are the cooks in the plant world. Their main function is to absorb sunlight to make plant sugars using the process called photosynthesis. Leaves are important to the earth’s atmosphere because they breathe differently than other life forms. The more leaves on the planet, the more carbon dioxide is absorbed and the more oxygen is released. Leaves are one of the key plant parts used in the scientific identification of plants. The shape, their location on a stem, and their outer edges (called margins) can all help to identify a plant.
Leaves are designed like an irrigation system: the xylem and phloem extend from the stem through the petiole (a small stem-like appendage that holds the leaf away from the stem) and into the leaf (called a blade) as veins. Leaves have a series of microscopic pores called stomata that reside on the underside of leaves. These tiny openings regulate the passage of water, oxygen, and carbon dioxide in the leaves.
The veins distributed in the blade form three distinct patterns. Parallel veins are aligned next to each other and this is common in the grass family. Pinnate veins extend laterally from the midrib (middle ridge) to the edge of a leaf (apple and cherry trees have this pattern). In a palmate pattern, the vein extends outward like a fan or palm (grape and maple leaves have this type of venation).
Deciduous broadleaved trees grow new leaves each year and drop them as the temperatures get colder. Conifers are plants that produce thin leaves that look like needles. Most conifers are considered evergreen, meaning they maintain leaves throughout the year. Anyone with a pine tree in their yard knows that conifers also drop their leaves; they do it throughout the year rather than all at once.
Leaf types: There are two types: simple and compound.
Simple – the leaf blade is a single, continuous unit
Compound – composed of separate leaflets arising from the same petiole
Leaf arrangement: How leaves are arranged on the stem helps with identification.
- Opposite – positioned across the stem from each other with two leaves at each node (mint family), two leaves at each node
- Alternate (spiral) – arranged in alternate steps along the stem, only on leaf at each node
- Whorled – arranged in circles along the stem
- Rosulate – arranged in a rosette around a stem with extremely short nodes
- Lanceolate – looks like a lance, longer than wide and tapering at the top
- Linear – Narrow much longer than wider
- Cordate (heart-shaped) Tapering to a point, upside-down heart and has a notch where the petiole is attached
- Elliptical – about 2-3 times as long as wide, tapering to an acute or rounded apex
- Ovate – Egg-shaped, tapering at tip
Margin patterns (edges of leaves)
- Entire – has a smooth edge
- Crenate – rounded teeth
- Dentate – teeth ending in an acute angle pointing outward
- Serrate – small sharp teeth pointing up to the tip
- Incised – cut into sharp, deep, irregular teeth or incisions
- Lobed – incisions that extend less than halfway to the midrib
- Conifer – needle-like leaves; many species are evergreen though they actually shed old leaves but not all at once
Leaf Identification Cards
A great way to learn about the identification characteristics of leaves.
- Collect a diversity of differing leaves while green (a second set of cards can be made with leaves collected in the autumn and a third set of cards can be made with conifer needles.)
- Flatten and press between two pieces of newspaper or construction paper. Place heavy books on top and allow them to sit for a few days. They will be drier and more brittle but will last longer. You can use them fresh from the outdoors
- Using card stock and self-adhering plastic (found in craft stores), place a leaf on each cardstock with just a dab of glue to hold in place. Cover the leaf in plastic, pressing down gently
Uses: Flashcards for ID, matching card games, or hang as art, use as greeting cards, placemats
Humans love flowers: the annual sales of the global flower industry is over $100 billion! They are often the showiest part of the plant and the primary part used for identification and classification. When Carol von Linnaeus created the classification system of plant nomenclature that we use to this day, he based it on flower structures and other reproductive parts of plants. The sole function of flowers is sexual reproduction and they develop enticing scents, bold colors, and delicate petal markings to attract a variety of pollinators (and apparently humans, too). This sensual strategy has evolved over millions of years to ensure the plants’ annual ability to reproduce.
Flowers contain the male and female reproductive organs of plants. The stamen is the male organ and consists of a pollen sac called an anther. The anther is held in place by a filament that ensures that the pollen is available to the pollinator. The female organ, called a pistil, is usually centered in the middle of the flower and includes a style, a stigma, and an ovary. The style is connected to the ovary and the stigma is at the top of the style. The ovary contains eggs that are housed in ovules. If an egg is fertilized through the process of pollination, the ovule develops into a seed.
Sepals are smaller green structures located at the base of the flower and their purpose is to protect the flower bud while it prepares to bloom. Collectively, multiple sepals are called a calyx. Roses often have noticeable sepals and the sepals of hibiscus grow into an edible fruit after the flowers bloom.
Petals are modified leaves that do much of the work of attracting pollinators. Through evolution, petals have developed bright colors, evocative scents (and a few smelly ones), and dramatic shapes. A group of petals is called a corolla, which has been studied extensively after Charles Darwin correctly suggested that the depth of corolla influenced the development of insect tongue lengths.
Plants that bear only one flower per stem are called solitary flowers. An inflorescence is a cluster of flowers on a plant and each flower in the cluster is called a floret. Inflorescences are divided into two groups: racemes and cymes. Florets that begin blooming from the bottom of the stem are racemes, and florets that begin blooming from the top of the stem are cymes.
Using a razor blade or Exacto knife and a pair of tweezers, dissect a flower by removing each part described above. Glue each part to a piece of cardstock, label the parts and cover with a piece of self-adhesive clear plastic.
Flower Power Art
- Using a hammer or mallet and watercolor paper, you can make some summer memories using the natural colors found in violas and cosmos. Explore this activity with other flowers, leaves, and steams.
- You can use a whole fresh flower or a petal. Place face down on the watercolor paper.
- Place a paper towel on top of the flower or petal. You may need to double up on the paper towel if using a whole or large flower.
- Pound on the paper towel until the entire flower or petal is pounded.
- Remove the paper towel and carefully peel away the flower to reveal the pounded flower print.
Fruit and Seeds
Botanically speaking, a fruit is a product that has been developed from a flower so an acorn, an ear of corn, a tomato, or winter squash are all considered fruits. Once seeds (fertilized ovules) begin forming, the ovary wall begins to develop a fruit, which can be fleshy and sometimes edible like an apple. The functions of fruit development are to protect the seeds and to encourage the distribution of the seeds when animals eat the fruit and eliminate the seeds.
The seed of a plant represents the fulfillment of a plant’s purpose: to successfully reproduce. Seeds contain all of the genetic information needed to develop into a complete plant. Because their sole purpose is to continue the species, seeds have evolved a variety of parts and mechanisms to ensure their survival.
Parts of a Seed
A seed contains three parts: the embryo, the endosperm, and the seed coat. Embryos are essentially miniature plants in a dormant state of development. Dormancy is a mechanism developed to ensure that seeds germinate and develop under favorable conditions.
The endosperm is a built-in grocery store. It supplies the proteins, carbohydrates, and fats necessary for the seed to grow until it has leaves and can produce food for the plant as it matures. A gardener friend loves to tell people that the seed is the best kind of party guest because it brings its own food!
The seed coat is the hard outer covering that protects seeds from disease and insects. It prevents water from entering the seed and initiating germination before favorable conditions are present.
Throughout the growing season, begin to collect seeds from a diversity of plants including vegetables, herbs, weeds, trees, flowers and shrubs. Glue them to a piece of cardboard and explore the diversity of seed shapes.
After taking time to observe and study the basics of botany, I have discovered an overwhelming curiosity about the magical world of plants and their determination to survive and thrive. There are many lessons to learn from plants.