Dichotomous Key

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Dichotomous Keys

Dichotomous Key for Picea (Spruces) – Plant 1 Image

Needles not clustered, directly attached to a twig
1. Needles lie flat
  1. Needles straight, ⅝-1” long, sharp, growing on all sides of branches………. Sitka Spruce (Picea Sitchensis)
2. Needles on all sides
  1. Needles straight, 2.5cm long (longer needles), sharp, four-angled, and roll between the fingers ………….. White Spruce (Picea glauca)
  2. Needles are short dark bluish-green, 1.5 cm long (shorter needles), blunt, hair ……….. Black Spruce (Picea Mariana)

Dichotomous Key for Plant Images

A. Is a tree

tree has needles

1A- Needles straight, 2.5cm long (longer needles), sharp, four-angled, and roll between the fingers ………….. White Spruce (Picea glauca) Plant 1

B. Is a flower

Has no petals

1A – A slim, cylindrical flower cluster, with inconspicuous or no petals, hair on leaves, over 20 stamens ………………. Plant 4 (Catkin)

2. Has petals

2A – has four drooping petals, hair on the stem ……………….. (Plant 2)

2B – has six petals, purples, over 10 stamens …………… (Plant 6)

Comments

2 responses to “Dichotomous Key”

June 27, 2021

Stefanie Ickert

Thanks Amanda,
the second key works. I was just looking for a key that would allow you to key out the plants, I was not looking for a specific ID to these. Plant 4 is also a tree. So in a way using needles vs. leaves would have been easier to separate the spruce from the rest and then, you could have used flower lacking petals for the willow (plant 4), while the other two have petals. When you are making a dichotomous key it is always good to have all the couplets be parallel. So when you use hairs on the stem for one of the plants in that couplet, the opposing couplet needs to also state something about the hairs on the stem. In this case you could have written lacking hairs on the stem or stems glabrous to use one of the fancy terms. Well done!

Reply
1. July 4, 2021
  
  Oona Martin
  
  Amanda – I admire that your took the time to make these descriptions. It captures your attention to detail. It’s tricky to hone in on a single characteristic when there are so many to choose from!
  
  Reply

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