The Key to Your Identity
- Students will
- Define a dichotomous key
- Develop and use a plant identification key
- Identify plant adaptations and their function
- Observe plant structures in summer and winter form
Identification keys, adaptations
Pa. Standards Addressed Doing the Activity
- Teaching Methods Assessment and Evaluation
- Background Extensions
- Getting Ready Resources
Pennsylvania Environment and Ecology Standards Addressed
- 4.7.7. Threatened, Endangered and Extinct Species
B. Explain how species of living organisms adapt to their environment.
Other Pennsylvania Standards Addressed
Science and Technology
Reading, Writing, Speaking and Listening
Teaching Methods: Observation, classification, small group
- One sample flower that students will recognize by name – make sure that leaves, flower, and stem are visible
- One sample flower that students will not recognize by name - make sure that leaves, flower, and stem are visible
- Different colors of yarn or flagging to mark flowers for each student group
- For each student group – 1 copy per flower of the Plant Characteristics sheet.
- Paper for identification keys
- Sample plant identification guides
- Sample dichotomous key
- Optional: different types of hats
A close look at plant’s flowers, buds, leaves, and stem will reveal many differences from one species to the next. These differences are adaptations that help them survive in their environment.
Many plant structures help with basic survival needs. A flower’s shape, color, size and scent are geared to insure pollination, so it can produce seeds. Tiny, green flowers like ragweed do not need to be showy because they depend on the wind for pollination. Large, colorful flowers are designed to attract animal pollinators like bees, birds, or butterflies. Light colored, strongly scented flowers often depend on a visit from nocturnal moths. Flowers are also structured to guarantee that the pollinator takes a little pollen with them when they move on to the next plant.
Leaves also come in a variety of shapes and sizes. They may have smooth or toothed edges, long or short stems, and hairy, waxy, or rough surfaces. Regardless of their appearance, leaves share a common function. They produce food for the plant through photosynthesis. The size of leaves can vary considerably, even on the same plant. Generally, leaves that are exposed to more sunlight are smaller than those in the shade. Oak leaves that receive abundant sunlight are more deeply lobed than leaves lower on the tree that may be more shaded.
The primary purpose of leaf shape is to capture sunlight, but shape serves other functions as well. A flattened rosette of leaves at the base of a stem can prevent other plants from crowding too close. Lobed or divided leaves permit wind to move through without shredding the leaf.
An important leaf function is the retention or removal of water. The dense, wooly leaves of Lambs-Ear and the wax-coated leaves of Shingle Oak prevent water loss, while the thick fleshy leaves of sedums allow for increased water storage. Tiny leaves have less surface area from which water can evaporate and low growing plants stay out of drying winds.
On the other hand, some plants in wetter areas have water-shedding devices to protect against rot. Asymmetrical leaves or leaves with sharp tipped edges help water to drip off quickly. Plants with lobed or divided leaves, like ash trees or strawberries, are more efficient at transpiration, which moves water out of the tree.
The stem or stalk of a plant may hold the leaves in the sun, provide support, or help avoid predators. A vine climbing a wall may benefit from more sunlight and a ground creeper may avoid being eaten. Flowers held up high may catch the attention of a pollinator or disperse their seeds on the wind.
Other adaptations help plants survive in a hungry world. Thorns, unpleasant tastes, and poisons defend against predators. Nuts and seeds encased in hard coats or spiny shells limit the number of animals that can eat them. Rough or fuzzy coverings on leaves and stems also discourage browsers. The hairy tips of stinging nettle break off easily when touched injecting chemicals that cause a stinging rash and the toxic chemicals in milkweed make most animals sick, but offer protection to the few that have adapted to use them.
A plant does not always look the same - it may change with the seasons. In winter, many plants have no resemblance to their spring or summer form. But winter identification is not necessarily more difficult. The plant’s structure and symmetry in winter is as significant as the leaves and flowers in summer. Spent flower heads, stems and seed pods reveal unique geometrical patterns. These structures are not only useful in identification, but also play an important role for the plant and its natural community.
Seeds and fruits often survive winter weather and provide valuable wildlife food. The stalks that support them rise above winter snow and keep the food reachable. In turn, the birds and mammals feeding on them, along with winter winds, help disperse seeds to other areas.
In addition to helping plants survive, all of these characteristics can be used to identify them. Identification keys are tools that are used to identify unknown things. Keys use characteristics to group things that have similar features. For example, all pink flowers could be in one group and all yellow flowers in another. Then the groups are divided into smaller and smaller groups until only one type of organism is left.
A dichotomous key is one type of identification key. Dichotomy means “division into two.” A dichotomous key divides the task of identifying something into a series of questions that are based on physical features. Each set of questions offers opposing answers to choose from. As you make choices, you eventually find out the name of the organism you want to identify. Using identification keys makes us take a closer look and helps us notice things we may otherwise never see.
Select 5 or more (depending on time, the size and level of the group, the variety of plants in your garden, and how complex you want the keys) plants for each group of students. Student groups can have the same flowers or different ones. It can be interesting to see how students take different approaches to identifying the same plant.
Mark each group’s plants with a different color of yarn or flagging. Give each group a color that matches one of the yarn colors – i.e. yellow group, blue group, etc. Students will develop a key for all flowers marked with their color.
Doing the Activity
In the classroom
- Explain that plants have adaptations that help them to survive in their habitat. These adaptations give the plant certain characteristics that we use to identify them.
- Hold up a flower that students would recognize by name. Ask students what type of flower you have. Ask them how they know that? What characteristics does the flower have that helped students to recognize it? (Flower color or shape, leaves, etc.)
- Tell students that if they didn’t know what type of flower it was, they could use an identification key. Explain that identification keys use characteristics to group things that have similar features. Then the groups are divided into smaller and smaller groups until only one type of organism is left. Show students examples of different plant identification guides.
- Tell students that a dichotomous key is one type of identification key. Explain how they work and show students an example of a dichotomous key.
- Use students to demonstrate how to make a dichotomous key. Select 5 students and have them come to the front of the room. Ask students what characteristic they could use to separate these 5 students into two groups. (Male/female, hair color, eye color, glasses, height, etc.) Tell them that with a dichotomous key it must split the group into two each time a choice is made. After the first split, have students continue to divide each successive group. Write the divisions on the board for a visual example. (For an example, see attached Sample Dichotomous Key to Students.)
- Option: Instead of using students or if further reinforcement is necessary, have students practice making a key with different types of hats. See attached example Sample Dichotomous Key to Hats.
- Once students understand the process, return to characteristics. Show students another plant that they would not recognize by name. Ask them what characteristics might help to identify the plant. Review the following: What shape is the flower? What color is the flower? How many petals does it have? What kind of leaves does it have? What shape are they? What do the leaf edges look like? Are they hairy or glossy? How tall is it? Does it stand upright or creep on the ground? What does the stem look like? Have students describe the plant in as much detail as possible.
- Tell them they will be using plant characteristics to develop a key for flowers in the garden.
In the garden
Break students into small groups. Point out the marked plants. Assign each group a color and explain that they will develop a key for all plants marked with their color.
- Quickly review some plant features that may be useful in the keys. Have each group closely examine their plants and complete a plant characteristics sheet for each plant.
- Using the characteristics sheets, have students develop an identification key. Remind them that the keys must use plant characteristics. You may choose to have students develop dichotomous keys or allow them to develop their own format. If students are developing a dichotomous key, remind them that the key must split the groups into two each time. (If time is limited have students develop keys back in the classroom and revisit the garden once they are completed.)
- Once completed, give each group the key from another group. Have them use the key to identify or locate the plants. Check results.
- As a group discuss which characteristics students used in the keys. Were there any plant characteristics you observed that you hadn’t noticed before? Which features were used most often in the keys? Which keys were most successful? Why?
- Discuss plant adaptations and their purpose. Why do you think there is so much variety among these plants? Why aren’t they all the same? How does being different benefit the plants? How do their different characteristics help them survive? What is the purpose of some of their features? Discuss benefits or purpose of color, shape, hair, thorns, growth pattern, etc.
- Have students repeat this activity in winter using plants that remain standing. How are these keys different from the other keys they developed? The focus will shift from color, leaves, and flowers to seed pods, stems, and buds. Discuss what features were more obvious in winter (buds, stems/branches, seedpods). Discuss why some plant stalks remain standing in the winter. Does this play any role in their survival? (Many plants continue to disperse seeds through the winter.) Does it benefit animals in any way?
- Completeness of characteristics cards.
- Accuracy and effectiveness of identification keys.
- Accuracy of responses and participation in adaptation discussion.
- Have students develop keys for trees, shrubs, or wildflowers on the school site.
- Have students use other plant identification keys such as Peterson Guides to identify plants on school grounds.
- Environmental Concern Inc. and The Watercourse, The Wonders of Wetlands, 1995
- Lingelbach, Jenepher, Hands on Nature, 2000
- The Conservationist, Jan.-Feb., 1980
- Vergine, Gary & Jefferson-Brown, Michael, Tough Plants for Tough Places, 1997