The second class in the Alaska Master Gardener course is about botany. I thought I was fairly knowledgeable about plants, but I am now learning that I know very little about them. For instance, did you realize that “plants make their own food from sunlight and water” and are the “primary food source for humans and other animals” – either directly or indirectly? I think I knew that but I am not sure.
This is not all they do. They also “provide fuel, replenish the earth’s oxygen supply, prevent soil erosion, slow down wind movement, cool the atmosphere, provide wildlife habitat, supply medicinal compounds and beautify our surroundings” (Sustainable Gardening – The Alaska Master Gardener Manual).
The botany chapter focuses on vascular plants – plants that contain xylem and phloem, which conduct water, nutrition, and food to the rest of the plant. There are two types of vascular plants: monocotyledonous (monocots) and dicotyledonous (dicots). Monocots are plants like grass that produce only one seed leaf (cotyledon), and dicots are broadleaf plants and have two seed leaves. These differences are important to know in order to understand the growth and development of plants. It is also important to know if one desires to kill a certain type of plant. One cannot kill dandelions by using something that will only kill grass and vice versa; however, there are mixtures that will kill both types of plants.
As you probably already know, there are three different classifications of plants: annual, biennial, or perennial. The classification is based on the life cycle of the plant and how long it takes to produce flowers, seeds, or fruits. Annuals are plants like marigolds and lettuce that live for only one growing season. They “germinate, grow, mature, bloom, produce seeds and die” all in one season. Annuals are either summer or winter plants; summer annuals complete their life cycle in spring and summer while winter plants complete their cycle in fall and winter. Knowing whether a weed is a summer annual or a winter annual is important in controlling its growth. Of course, there are very few plants that will grow during a winter in Alaska, and some plants that grow in the winter in warmer climates become summer annuals in Alaska.
Biennial plants take two growing seasons to complete their life cycles. The first season they produce vegetation (stems, leaves, etc.); they usually live through the winter and produce flowers, fruit, and seeds during their second growing season. Some examples of this type of plant are Swiss chard, carrots, beets, sweet William, and parsley. These plants can “bolt” and go to seed during their first season because of the long hours of sunshine in Alaska.
Perennial plants live for more than two growing seasons and are divided into two classifications: herbaceous perennials and woody perennials. Herbaceous perennials “have soft, non-woody stems that usually die back during the winter” with new growth coming from the crown in the spring. A delphinium is a good example of this type of perennial. Woody perennials “have woody stems that withstand cold winter temperatures” such as trees and shrubs.
Plants have both external parts and internal parts. As in most living things, cells “are the basic structural and physiological units of plants. Most plant reactions (cell division, photosynthesis, respiration, etc.) occur at the cellular level. Plant tissues “are organized groups of similar cells that work together to perform a specific function.” Plant cells have “all of the genetic information (encoded in DNA) necessary to develop into a complete plant.”
The external parts of plants – roots, stems, flowers, fruits, and seeds – are known as organs. An organ is “an organized group of tissues that work together to perform a specific function. These structures can be divided into two groups: sexual reproductive and vegetative.
Sexual reproductive parts produce seed; they include flower buds, flowers, fruit and seeds. Vegetative parts … include roots, stems, shoots, nodes, buds and leaves; they are not directly involved in sexual reproduction. Vegetative parts often are used in asexual forms of reproduction such as cuttings, budding or grafting.”
Roots are very interesting things and have two major types: primary and lateral roots. The primary root is the main root that usually goes straight down, and lateral or secondary roots grows out of the side of another root. If the primary root grows long and has few secondary roots, it becomes the main part of the root system and is known as a taproot. Examples of taproots are carrots or dandelions.
If the primary root does not continue to elongate and produces lateral or secondary roots, it becomes a fibrous root system, the network of roots found on most plants. Roots grow best in loose, well-drained soil. Some vegetable crops are simply roots that have enlarged, such as sweet potatoes (swollen tuberous roots) and carrots, beets, rutabaga, parsnips, turnips and radishes (elongated taproots).
Stems can be shoots, twigs, branches, or trunks. They “support buds and leaves and serve as conduits for carrying water, minerals and food (photosynthates). Stems place the leaves in favorable positions for exposure to light. The vascular system inside the stem forms a continuous pathway from the root, through the stem and finally to the leaves. It is through this system that water and food products move.”
The “plumbing” system of a stem consists of xylem, phloem and vascular cambium. “Xylem tubes conduct water and dissolved minerals; phloem tubes carry food such as sugars. The cambium is a layer of meristematic tissue that separates the xylem and phloem and continuously produces new xylem and phloem cells. This new tissue is responsible for a stem’s increase in girth.” Both monocots (grass) and dicots (broadleaf plants) contain xylem and phloem, but they are arranged differently; in monocots they are paired in bundles and in dicots they form rings inside the stem. The phloem is the outer ring (becomes the bark of the tree), and the xylem forms the inner ring. Sapwood is the newer xylem, and heartwood is the older xylem.
Stems have nodes where buds are formed. Stems also come in different types. Stems can be long (branches of trees or strawberry runners) or have short distances between the nodes (such as strawberry crowns). They can grow both above ground and below ground but must have buds or leaves. Above ground stems are crowns (strawberries, dandelions), spurs (fruit-bearing stems on apple, cherry, and pear trees), or stolens (strawberry runners or spider plants). Stems that grow below the ground are called rhizomes (irises), tubers (potatoes), bulbs (tulips, onions), corms ( gladiolus, crocus). There are also tuberous stems (tuberous begonias and cyclamen) and tuberous roots (dahlias and sweet potatoes).
The main function of leaves is to absorb sunlight, which is needed to produce plant sugars through photosynthesis. Leaves are flat in order to present as large of an area as possible to absorb sunlight. A leaf has a midrib down the center of the leaf with the blade on either side. The leaf is held to the stem by an appendage known as a petiole, which is attached to the stem at a node. The petioles come in various lengths and may be missing entirely. The leaf blade is then “described as sessile or stalkless. A celery stalk is a leaf petiole.” Leaves come in various types and sizes and have one or both of the following purposes: plant identifiers and/or food (kale, lettuce).
Flowers are the most beautiful part of a plant and have the sole purpose of sexual reproduction. “Their beauty and fragrance have evolved not to please humans but to ensure continuance of the species. Fragrance and color attract pollinators (insects or birds) that play an important role in the reproductive process.
“Flowers are important for plant classification … [and] knowledge of flowers and their parts is essential for anyone interested in plant identification.
“Flowers contain a stamen (male flower part) and/or pistil (female flower part), plus accessory parts such as sepals, petals and nectar glands…”
Fruit is the fertilized, mature ovules (seeds) plus the ovary wall. It may be fleshy (apple) or hard (acorn). Some fruit have the seeds enclosed within the ovary (applies, peaches, oranges, squash, cucumbers) while the seeds of other fruits are on the outside of the fruit tissue (corn, strawberries). “The only part of the fruit that contains genes from both the male and female flowers is the seed. The rest of the fruit arises from the maternal plant and is genetically identical to it.”
There are simple fruits that develop from a single ovary. Fleshy simple fruit are cherries, peaches, pears, apples, tomatoes, squash, cucumbers and eggplants. Dry simple fruits are papery, leathery, and hard, such as peanuts and walnuts.
An aggregate fruit comes from a single flower with many ovaries (strawberries, raspberries, etc.) Multiple fruits develop from a “tight cluster of separate, independent flowers borne on a single structure (pineapples and figs). We consider some fruits to be vegetables even though they are technically fruit: tomatoes, papers, cucumbers, squash, green beans and eggplants.
Seeds contain “all of the genetic information needed to develop into an entire plant. It is made up of three parts…. The embryo is a miniature plant in an arrested state of development. It begins to grow when conditions are favorable. The endosperm or cotyledon is the seed’s built-in food supply and is made up of proteins, carbohydrates or fats (orchids are an exception). The third part is the seed coat, a hard outer covering that protects the seed form disease and insects. It also prevents water from entering the seed and initiating germination before the proper time.”
This was a lot of information for me to process in one day; however, I find that I understand the material much better as I attempt to explain it to my readers. I will continue sharing information as I study more about basic botany; part 2 will come later.