Plant Dissections

Chamerion angustifolium (Onagraceae) Fireweed

Cornus canadensis (Cornaceae) Bunchberry

Geranium erianthum (Geraniaceae) Woolly Geranium

Polemonium acutiflorum (Polemoniaceae) Tall Jacob’s Ladder


  1. These are gorgeous Oona! Great job on using ThingLink and describing and dissecting the flowers. The bunchberry has a hypanthium that is the result of fusion of sepals (which turn darkish red to purple at maturity), petals (white) and stamens. The hypanthium has densely appressed hairs which you show nicely on your images. The fruit is a drupe (stony endocarp). If it were a nut, the whole pericarp would be stony (the mesocarp is fleshy in Cornus) and we need to have an involucre subtending each fruit, which is lacking here as well. Great you were able to capture the details of the anther filaments in the woolly geranium, it is fun to watch when the solitary seeds flung out when the carpel suddenly splits. For Polemonium, I would not describe it as having a hypanthium, by definition a hypanthium is the fusion of sepals, petals and stamens. In Polemonium you can clearly find the sepals fused into a ring (synsepalous) and a ring of the petals fused (sympetalous) with the stamens adnate to the corolla (epipetalous). The ovary is free from either one of those rings, and each is inserted below the ovary, thus hypogynous. I think the base of the ovary and the base of the calyx perhaps appear fused due to the common stem base they are inserted on. Your photography is excellent, and it shows your command of the characters that are important for identification. I hope you enjoyed making these dissections. It sounds like you are very well versed in botanical jargon now :). If you are continuing to observe flowers, try to make some dissections of the ovaries in both cross section and longitudinal section. It is fun to see the placentation types this way. Fabulous work, so proud of you!

  2. Oona Martin

    Thank you for your detailed feedback. I’m glad you enjoyed the images. I did have a good time with these and I was grateful to be able to work at my own speed since I spent quite a bit of time with each one. I did not expect the Cornus to be made up of little flowers in this way and I was pleased to be able to figure that out (mostly). I appreciate that you answered my questions and provided this additional information. I have updated the Thinglinks in response.
    Thank you!

  3. Excellent! Thanks for updating your ThingLink pages. I really love the semi close-up of the Cornus fruits, so beautiful showing the appressed hairs on the ovary. I have not look at these under a microscope since they are so straightforward to ID, but some of the features are really stunning when you look closely.

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