SC Master Gardener Course: Basic Botany

Wendy S. Delmater
By Wendy S. Delmater on Wed, Jan 8, 2014 - 6:09pm

Clemson Master Gardener Training Manual

As many of you know, I've been taking a Master Gardener course online through the Clemson University Cooperative Extension. I'm doing a series of posts on the various topics studied, to try and share what I've learned. I will strive to give you useful information for any climate. This post will be about Basic Botany. It will be very long, but I will try not to get too technical!

Botany is the study of plants. Horticulture is the art and practice of growing things for food, beauty, and profit, and it includes everything from a farm to a garden to landscaping to forestry. Understanding basic botany will help you identify plants and plant diseases.

There are two basic kinds of plants we cultivate: angiosperm and gymnosperm. The 260,000 angiosperm plants have enclosed seeds, like the pit of a peach or the seeds of a bell pepper. The 760 gymnosperm plant varieties—more primitive—have “naked seeds.” Examples of gymnosperm plants are gingko, moss, pine, cypress, and fir.

Angiosperms are further divided into two main groups: monocot and dicot. Moncots have one seed leaf, parallel veins in their leaves (like hostas and tulips), flowers with three petals (or multiples of 3) and a discontinuous vascular system: their stems are not arranged in rings like a tree or straw, but rather the water comes up through the entire stem. Dicots make up 97% of all plants, and have two seed leaves, branched veins, circular vascular tissues, and flowers with 4 or 5 petals (or multiples of 4 or 5).

Plant tissues. The growing parts of plants are called meristematic tissue. This can be on the growing ends of roots shoots (apical meristems); lateral meristems make perennial plants grow thicker and stronger. Grasses have intercalary meristems at the base of their blades, which is why grasses can be grazed or mowed and still grow. Then there is permanent tissue, like a plant's epidermis (skin) or vascular tissues. And then, there are roots.

Roots are very important, as they are the only way most plants can obtain water and mineral nutrients. They come in two basic types: taproot systems and fibrous root systems. A taproot, like a carrot, is a main root that angles straight down. Fibrous roots create a mat of fine hairs, branching out from the plant's base. Some plants have both types; others adapt to environmental conditions by perhaps growing a taproot in a drought.

Roots have a root cap, which protects the meristem (growing end) and root hairs that increase the surface area for absorbing water and nutrients. Vascular tissue—xylem and phloem in the center of the root—are called the stele. There is a region in between the root's epidermis and stele called the endodermis, which regulates water and nutrients coming into the roots.

Stems & Shoots. These structures provide support for the leaves as a plant reaches for sunlight and transports nutrients and water up from the roots. Stems also transport products of photosynthesis down to the plant. There are leafy shoots that have leaves and there are flowering shoots that have flowers. Shoots have nodes where leaves or buds attach. The sections between nodes are called internodes.

Stems can be herbaceous (non-woody) or woody. Woody plants have secondary growth of tissues like bark and expanding tree stems. This secondary growth allows xylem and phloem to grow outwards as the woody plant stem expands. In woody plants. the stem becomes a twig after it grows bark (bark is also known as cork material, FWIW).

Stems have many forms, not just the branches on a tree. There is the runner, or stolon, like a strawberry uses to spread. Tubers like potatoes and bulbs like onions are modified stems. Rhizomes and corms are also stem modifications. (note: tuberous roots like sweet potatoes are not stem modifications: they have no buds, nodes, or internodes.)

Now, lets talk about what the xylem and phloem do. Xylem is on the inside of the dicot stem and transports water and nutrients UP. Phloem is slightly further out from the center and transports plan manufactured substances UP and DOWN. Trees' xylem and phloem are just inside their bark, and are called sapwood. Herbaceous plants often have green stems since photosynthesis happens there, but not always. Moncots have a different structure for their vascular bundles: they are dispersed throughout the stem, although phloem is toward the center and xylem is more toward the outside. Moncots have no dead tissue in the center as they grow, no heartwood: the whole structure grows. In woody monocots like palm trees, the whole trunk is alive.

Buds. Buds can be along the stem (auxiliary buds) or at the ends of growing tips (terminal or axial buds). They can produce leaves and shoots (vegetative buds), flowers, or both (mixed buds). Buds are most noticeable on deciduous trees when the leave drop. The bud will be above a leaf scar, where the old leaf fell off. (There are other types of buds, such as adventitious buds that grow at the edge of a leaf like suckers.) Brussels sprouts, head lettuce, and cabbage are all edible buds. Cool fact: you can tell how old a woody deciduous plant is by its terminal bud growth scars!

Leaves. Basic leaf parts are the midrib, the blade (on either side of the midrib) the petiole (leaf stem). Celery and rhubarb are edible petioles. The petiole is not always present; leaves that attach directly to the stem are called sessile, stalkless leaves. Stipules are leaf-like organs usually found at the base of a petiole or at the node of a stem like on strawberries or geraniums. Sometimes stipules are fused to the base of the petiole (roses do this). Stipules are useful for identifying plants.

The inside of a leaf is like a sandwich. The top and bottom, the “bread” of our sandwich is the epidermis, the skin of the leaf. The top is a waxy cuticle that protects the leaf from water loss and the bottom has openings to regulate water, carbon dioxide and oxygen in and out: stomata (singular, stoma). These are like the lungs of the leaf. Our sandwich filling is the mesophyll, where photosynthesis occurs. Xylem and phloem run through the mesophyll, usually with the xylem on top. Note that pine needles have a very similar structure.

Leaf types. Here we can really start learning things that will help us identify plants! Take a look at this chart of leaf types:

A simple leaf has a blade that's one continuous unit. A compound leaf has several leaflets coming from the same petiole. A deeply lobed leaf may look like a compound leaf, but if the leaflets are connected by a narrow band of blade tissue, then it's still a simple leaf. If the leaflets have separate branching stalks then it's a compound leaf.

Take a look at the leaf blade margins: are they sawtooth, lobed, wavy? Then look at the leaf's veins: are they parallel veins (monocots) or netted? Net-veination can be either pinnate or palmate. Pinnate veins extend laterally from the midrib to the edge, like in a beech tree leaf. Palmate veins radiate out from the base of the midrib, like a fan.

Another way to identify a leaf is by its texture. Leaves can be

  • coriaceous – tough, leathery.

  • Downy – covered with shirt, soft hairs

  • hirsute – coarse, stiff hairs

  • hispid – rough, with bristles, stiff hairs, or prickles

  • pubescent – a hairy surface

  • scabrous – rough to the touch with a sandpapery feel

  • smooth – shiny, hairless surface

  • succulent – juicy, fleshy, soft and thickened in texture

  • tomentose – covered with matted, wooly hairs

Whew! That's a lot of choices.

Now, let's talk about how the leaves are arranged. Alternate or spiral leaves are arranged with one leaf per node, with each leaf located on the stem opposite the leaves directly below or above it. Opposite leaves are positioned across the stem from each other with two leaves per node. Whorled leaves are arranged in a circular fashion along the stem. Rosulate arrangements have basal leaves that form a rosette around the stem with extremely short nodes.

Then we get to the weird adaptations. Grapes use tendrils (modified stem parts) to curl around things, to climb, while ivy uses adhesive disks. Most tendrils are leaf modifications (like peas). Spines are leaf modifications, thorns are modified branches. The prickles on roses are mistakenly called thorns: actually, they are modified epidermal cells. Bracts are leaves that look like flowers., like on dogwoods and poinsettias.

Okay, now let's discuss flowers. Gymnosperm plants like conifers make seeds directly, but angiosperm plants produce flowers, which in turn create fruit and seeds. Flowers are a great way to identify plants. Here is what you need to know about plant parts for ID purposes.

The stalk of a flower is called the peduncle. The stalk of an individual flower in an inflorescence (flower cluster) is called a pedicel. The receptacle is the enlarged tip of the pedicel where the flower structure is attached.

A typical flower has four parts: sepals, petals, stamens, and carpels. Petals and sepals are not reproductive organs, but may use color to attract pollinators. Sepals are green, leaf-like structures to protect the other flower parts collectively known as calyx. These are the caps on strawberries, to give you a visual. Petals, as you know,.are the brightly colored parts of flowers – collectively known as the corolla. Petals and sepals together are known as the perianth.

The fertile parts of the flower are the stamen and carpel. The stamen is the male part of the flower. It has a pollen sack called an anther, and a long supporting filament to either disperse the pollen via wind or make it available to pollinators. The carpel contains ovules that develop into seeds after being fertilized. An individual carpel or a bunch of fused carpels is a pistil. The pistil is the female part of the plant, and contains a stigma, a style and the ovary. The stigma is at the top and the style is a tube that connects the stigma to the ovary.

A “perfect” flower has all four parts: sepal, petals, stamens, and carpels. Some flowers are missing parts and are “imperfect” (example: hollies.) This gets really important if a plant is not self-fertile. Pistillate flowers have no male; staminate flowers have only male parts. Sterile flowers have no reproductive parts at all. Plants that are self-fertile because they either have perfect flowers or male and female flowers on the same plant are called monoecious (Greek: one house). Dioecious plants have a male and female variety (examples: kiwi, asparagus) . You have to plant at least one of each.

Some flowers are one-per stem, like daffodils. Those are “solitary flowers.” A cluster of flowers, or an inflorescence, can be a spike (tuberose), a raceme (hyacinth) , panicle (grasses), corymb (yarrow, hydrangea), or umbrel (carrot, onion). One thing you may find interesting is the composite flower head, like on sunflowers: a central region of disk flowers surrounded by ray flowers. Chrysanthemums and dahlias have composite flower heads, but you cannot tell the two types of flowers apart.

Very odd fact: it takes two sperm to fertilize a female flower organ to make a full seed: one for the egg and one for the two polar nuclei that grow the seed's food.

Fruit. In a botanical sense, “fruit” is fertilized flower tissue. Some botanical fruits are called veggies: corn, tomatoes, cukes, eggplant, or squash for example. Fruits can be simple, aggregate, or multiple.

Simple, fleshy fruits come in five types: berry, pepo, drupe, pome. and hesperidium. Botanically speaking, berries are fruit that are all-fleshy, like eggplants, grapes or tomatoes. A pepo is a berry with a hard rind, like cucumbers, pumpkin & squash. Hesperidium are citrus fruits with their leathery rinds. Drupes are stone fruits: cherries, peaches, olives, plums etc. Pomes are fruits where the walls of the former ovary are papery and dry, like apples, pears, and quince. Those are the fleshy fruits. Simple dry or dehiscent fruits split open at maturity and release many seeds. They can have a capsule (poppy), follicle (larkspur), pod (pea), or a silique (radish, kale)

An aggregate fruit is a cluster of fruits from a single flower with many ovaries. Each ovary must be pollinated or misshapen fruit occurs. Blackberries and raspberries are aggregate fruits (and drupes with tiny stones.) An achene is a fruit with clusters of ovaries turned into fruit on the outside and a fleshy interior: think strawberries.

Multiple fruits come from a cluster of separate flowers. And take surprising shapes. Mulberries are a multiple fruit, as are pineapples: the fruits in a pineapple fuse into one large mass. Figs are a multiple fruit made of many tiny drupes inside a fleshy receptacle (and are pollinated by wasps that crawl into that receptacle, but that's another story.)

Okay, now lets talk about seeds. A seed has a seed coat (testa) with an embryo inside that looks just like a miniature plant. If you care, the seedling has a tiny root called a radicle, a tiny shoot called a plumule, and cotyledons—tiny seed leaves—one leaf (monocot)or two leaves (dicot.) The endosperm is the food the seedling lives on during germination.

Seeds spread lots of ways. Animals eat them but cannot digest the seed coat and leave them in their droppings, wind blows them around, burrs catch on clothing and fur to hitch a ride, and some seeds even have wings (like maples). And of course some seeds come from catalogs, neighbors, or last year's garden plants. (*smile*)

Seeds that can germinate are said to be viable. Germination begins when the seed absorbs water through the seed coat. Many types of seeds will only sprout in a specific temperature range, so check your seed packet or do your research.

Classifications of horticultural plants. There are three classifications: annuals, biennials, and perennials. Annuals finish their life-cycle in less tan a year, being killed by winter's frosts or summer's heat. Biennials live two years, making edible food the first year and going to seed the second: carrots are in this group. Perennials come back every year. They may not live forever—asparagus,for example, only lives 25 years, but they have staying power. Perennials are classified as herbaceous (non-woody) or woody. They are perennials based on the minimum temperatures they can tolerate. In colder areas, a perennial might have to be treated as an annual.”Hardy” plants are classified based on the cold and heat they can tolerate. Things that are injured by frost are classified as “tender” and items that grow best in cooler months are cool-season crops (peas, broccoli.)

Form or structure classifications for woody plants: Vine, ground cover, shrub, or tree are the main categories. Fun fact: some vines grow clockwise, others counterclockwise.

Classification via leaf and needle retention: Deciduous plants lose all their leaves once a year. Semi-evergreens keep their leaves most of the year. Evergreens keep their leaves all year and come in broad leaf (southern magnolia, boxwood, holly) and needle-leaf varieties.

I am NOT going to go subject you to nice long description of taxonomy – the scientific names for plants. You want to learn about that? See this link. http://en.wikipedia.org/wiki/Plant_taxonomy I will just mention in passing that a lot of taxonomic names and classifications have changed once plant gene-typing was done. And I will point out that a plant may have several common names but only one scientific name per cultivar. If you want really good information on a plant, I suggest you go the the USDA Plants database website http://plants.usda.gov/java/

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