IDENTIFICATION OF WINTER WEEDS

PURPOSE: To identify some common winter weeds by the use of a dichotomous key and determine their methods of seed dispersal.

MATERIALS:  Winter weed samples, Key to Winter Weeds

INTRODUCTION:  Weeds are simply plants growing where they are not wanted or where they were not planted.  They can be found in city lots, along roadsides, in open fields or forest clearings.  Typically such plants are aggressive colonizers that can tolerate a wide range of soil and climatic conditions.  Many of these plants, now widespread in North America, were introduced from Europe either deliberately or accidentally.

Those plants with dead stems that remain standing throughout the winter may be called winter weeds.  The seeds of most of them are dispersed throughout the autumn and winter seasons.

One of the major concepts in biology is that structure is related to function: the way an organism looks is related to what the organism does.  This is called "complementarity" of structure and function.  For example, plants show differences in their fruit and seed structures which are related to their functions in seed dispersal.  To get the most from a study of winter weeds, you should be aware of the distinctive features of each species.  Species vary in color, size, habitat, their use by animals, and their methods of seed dispersal.

HOW TO USE A DICHOTOMOUS KEY: The word dichotomous means "separating into two groups, which describes the kind of choices that must be made in using such a key. Starting at the top of key you much choose between 1A and 1B. The choices are opposites. The plant you are trying to identify MUST fit into one group or the other. After you have made your decision, you are given the name of the plant or directed to go to the number of the next choice. Continue making decisions until you arrive at an identification.

PROCEDURE:

A. Arranged around the room you will find samples of common winter weeds identified by letter.  Use the dichotomous key to identify each plant by its common name. 

B.  Record your observations on the data sheet.  Look at seed structures for clues to their methods of seed dispersal.  Remember that plants have evolved different structures that respond to the same agent of dispersal such as wind or animals.

QUESTIONS:

1. Which of the winter weeds that you identified are most commonly seen in open fields or along roadsides in the winter?

2. What are some of the differences among the seeds of winter week species?

3. Which plants have seeds that you are likely to find attached to your clothing after a walk through the fields?

4. Which plants have seeds that you are likely to see floating in the air?

5. What are the two most common agents of seed dispersal among the plants you observed?

6. What specific structural characteristics enabled you to determine the plant's method of dispersing its seeds?

7. On the basis of size and quantity of seeds produced, which of the plants you identified may provide winter food for birds or small mammals?

8. Which seeds may provide nesting materials for birds or small mammals?

WINTER WEED IDENTIFICATION DATA SHEET