Dichotomous Key

Dichotomous Key to photos 1-4 Module 2

A. Plant lacking flowers, leaves needle-like, evergreen,

cones. ….. Plant 1

A’.   Plant with flowers, leaves divided into peduncle and expanded blade, deciduous, lacking cones.

B.   Flowers that lack petals, yellow. …Plant 4

B’.   Flowers large with pedals, white or blue/violet

C.   Four pedals per flowers, pedals white …. Plant 2

C’.   More than four pedals per flower, pedals

blue/violet … Plant 3

 

3 Comments

  1. Thanks Belinda, well done! When we make keys we try to be completely parallel. In the example it is not so much of an issue, since there are only four different plants. But if you think about a genus of plant with more than 20 species, each couplet will have to be carefully crafted to make it a more concise key. So for A’ to be parallel, you would state A’. Plant with flowers, leaves divided into peduncle and expanded blade, deciduous, lacking cones. There are evergreen flowering plants, some with needle-like leaves, there are even some that produce cone-like structure, such as she-oak [Casuarina]. Plant 4 is a willow, so there are pistillate catkins that lack petals and only the ovary is shown with a bract and nectary at the base, as well as staminate catkins that lack ovaries and the catkin is composed of stamens only. Have a look at some willows and see if you want make out the different catkins. Best, Steffi.

    1. dedowling

      First, I’ll start by saying I think you did a great job describing plants 1,2,3 and 4. Using your Dichotomous Key I was able to identify Plant 1 with ease. I think that some of your identifiers could have been less descriptive. For instance, A’ could simply just say “Plant with flowers.” Another important element of Dichotomous Keys is directing the reader to the next distinguishable characteristic. A’ should direct the reader to B, and B’ should direct the reader to C. Another thing is making sure each letter is mutually exclusive from other letters. B’ should just state “Flowers with petals”, and distinguish between the colors in C and C’. Overall I could follow your key as it is written! 🙂

  2. Derek

    BeLinda, great work with this. I was able to identify each plant picture using your dichotomous key. I think that it works well to pull out the most different plant first (Plant 1) as you did. I might suggest removing the words ‘evergreen’ and ‘deciduous’ as those generally refer to exclusively trees and shrubs (woody plants) and the group of plants that we are keying out involve herbaceous plants as well.

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