Background

Imagine that you have been given the task of studying plants, and you discover there are thousands and thousands of different plants from around the world for you to choose from. How and where would you begin to make sense of them all?

Scientific Classification
To bring order to this daunting task, botanists have developed a scientific classification system to group similar plants together. They make note of details about plant anatomy (especially that of flowers, fruit, seeds, and leaves) along with plant growing habits, and then use these characteristics to divide plants into categories. This system eases and organizes their scientific pursuits.

A few examples from the cucumber family

Although there are many tiers of categories, one useful to gardeners is plant family. These aren’t nuclear families with fathers, mothers and children, but extended families – like cousins – of plants scientist believe are related by shared characteristics.

Still wondering how gardeners benefit from knowing what family a plant is in? Well, in addition to sharing similar structures, species within a plant family often have similar growth habits and growing needs. Therefore, if you know how to grow one member of the family, you have a clue about how to grow other members of the family. Members within a plant family are often bothered by the same kinds of insects and disease pests; this information comes in handy when you’re identifying problems and choosing plants appropriate for your environment.

The squash family -- which includes cucumbers, melons, gourds, pumpkins, winter and summer squash -- is a good example to illustrate shared growth habits within a family. All sport separate male and female flowers on the same plant. Why is this information is important to gardeners?

A female butternut squash flower that has been pollinated. (See the baby squash?)

As plants mature, the first flowers to blossom are usually male; female flowers emerge later. Novice gardeners are often discouraged when their apparently thriving cucumber or pumpkin plants keep dropping flowers without producing any fruit! This is because those first male flowers aren’t capable of producing any fruit on their own, so they wither and fall. By knowing the progression of flower appearance, you won’t lose hope for a crop.

Plants in the squash family depend on pollinators in order to set fruit. Since the reproductive parts are on separate flowers, pollinating insects like bees are necessary partners that move pollen from the male to the female flowers. So, gardeners who cover their young plants with row covers to protect them from pests or cool weather need to uncover the plants when they begin to flower -- otherwise, pollinators can’t reach the blossom, and, and plants won’t produce fruit. (It also indicates the importance of encourage pollinators to come to your garden!)

Life Cycle Classification
Most students can recite a basic plant life cycle: seed, plant, flower, seed. Although the steps in this process are the same for all seed-producing plants, life cycles vary in length and schedule. This gives botanists and gardeners another way to categorize plants, this time into three main categories: annuals, biennials, and perennials.

Annuals complete their life cycle during one growing season; they die after they produce seeds. For gardeners, there are two main types: cool-season annuals and warm-season annuals. Many common vegetables are annual plants, and knowing which temperature class they’re in can help you decide when to plant them. Common cool-season annual vegetables include lettuce, cauliflower, and spinach. Common warm-season vegetables include squash, tomatoes, and beans.

To witness a common vegetable's biennial life cycle, leave a cabbage or two to mature in the garden.

Biennials live for two growing seasons. The first year they store energy; in the second year, they produce seeds and die. It’s more common to see flowers classified as biennial than vegetable crops. Why? Well, consider these examples of biennial vegetables – carrots, onions, cabbage, and beets. Unless you want to experiment with observing their blossoms or saving seeds, you harvest the edible plant part – in the case of our examples, the roots and leaves – during the first growing season, eliminating their option to blossom and produce seeds. Gardeners plant some biennial crops in early fall and harvest them the following spring or summer before they blossom.

Perennials are plants whose life cycle is longer than two growing seasons. We divide them into three more categories:

Classification by Use
Another way to classify plants is to lump them into groups based on how we use them.

For example, according to the Herb Society of America, the word herb is used to describe plants “valued for their flavor, fragrance, medicinal and healthful qualities, economic and industrial uses, pesticidal properties, and coloring materials (dyes)." This definition creates a large category of plants that includes annuals, biennials, and perennials in multiple families.

They all have seeds...they must be fruits.

We also categorize fruits and vegetables by use. Botanically speaking a vegetable comes from the vegetative parts of a plant (root, stem or leaf). A fruit is from the reproductive structure of the plant and contains the seeds. Based on this definition many common vegetables like tomatoes, squash, and cucumbers are actually fruits.

But when it comes to categorizing them by use, vegetables are defined as edible plant parts eaten with the main course of a meal, and fruits are defined as plant parts eaten as a dessert or snack. This classification system places common botanical fruits like cucumbers in the vegetable group. Don't quibble, now: These are official definitions according to a U.S. Supreme Court ruling! Read more about how lawyers and judges got into the act of classifying produce: I Say Tomayto, You Say Tomahto

Summary
Plant classification provides botanists and gardeners with a way to organize plants to make them easier to study and understand. Introduce your students to classification concepts by challenging them to create their own system. This month’s lesson, Grocery Store Botany, provides activity details and resource information to help get you started.

 

 

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