Potentially misunderstanding a dichotomous key

Nature Talk
1

Hello everyone I am learning how to ID convolvulus-es. and I came across this wonderful research paper with many dichotomous keys per region, in the key for my region (north africa) I found the following:

Page 36

So they way I understood this, is: sepals with distinct parts = C. Tricolor and sepals that look the same all the way through = C. meonanthus

before starting to identify I looked at a few observations to see how this difference looks like in real life and I found these 2 clear images:

C. tricolor
C. tricolor1920Ă—1440 557 KB

C. meonanthus
C. meonanthus1365Ă—2048 407 KB

note: both of these photos are from each of the species taxon pages respectively

to me this looks like the exact opposite of what I just read, C. tricolor has greenish sepals while C. meonanthus has green and brown parts.

I feel like I am misunderstanding something.

More generally this is one of the things I struggle the most with while learning how to identify. I don’t know where the sepals they are talking about are supposed to start and end, and what the “distinction” should look like in real life. I faced this problem while learning other species but this is the clearest one yet.

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I’ll try to help here, though I don’t know these two Convolvulus. I remember having similar quandaries when I was first learning how to use dichotomous keys. Sometimes it comes down to knowing how specific terms are being used by the authors of the key, and sometimes a key just isn’t as rock-solid or clearly worded as you might like. A caveat: I’m not familiar with either species or with European plants, so I can’t be 100% certain those two Research Grade images are correctly identified (even though they are included as reference photos for each species).

I looked at more Research Grade photos of each species, especially photos showing the sepals, and I also read the descriptions of both species and looked at the line drawings included in the paper. The drawings of sepals for both species are shown on page 144.

Sepals for Convolvulus tricolor (images 42, 43, 44) are oddly shaped, somewhat oblong with a constriction in the middle. I think that is what is meant by “sepals with distinct…lower and upper portions” in the description and key for C. tricolor. Notice I left out “different coloured” in that quote. The upper and lower portions are differently coloured, apparently, but in combining those two traits (different upper & lower portions, differently coloured) into one phrase, the key makes it sound like the main difference is the colour, rather than the separate portions. I tracked down some RG observations of C. tricolor that show these constricted sepals - the clear lower portion adhered to the flower base and the green part a bit reflexed outward: https://www.inaturalist.org/observations/73783286 and https://www.inaturalist.org/observations/44304920. The colour difference is a more subtle thing (clear versus green) and I’m not sure I can see it in the photo of C. tricolor that you linked above. Those sepals look different – overall narrower, without an obvious constriction and clear portion below – but I’m not qualified to say whether that is truly tricolor or not. And there are apparently different varieties of C. tricolor, each of which may have a slight variation on two-part sepals.

Turning to C. meonanthus, the photo you included shows a darkened reddish tip on the sepal, but in plants, that sometimes is a function of age and not a diagnostic trait. I don’t know in this case, but looking at other RG observations of C. meonanthus (https://www.inaturalist.org/observations/207658686, https://www.inaturalist.org/observations/207658686), the presence and amount of red seems variable.

With plants, one photo (or specimen, if you have access to a local herbarium) often isn’t enough, because each individual plant is unique (and my mentor always said, “Plants don’t read the books”). I hope this is helpful, and I’m sorry it is complicated! But kudos to you for learning to use keys and reading monographs and trying to figure it all out.

3

Thank you so much for taking the time to do all this research, I really appreciate it!

looking at more pictures of each definitely helped because I now see the 2 sepal parts in C. tricolor, but before reading your description I thought any anomaly in the sepal was the “distinction” mentioned in the key, which obviously didn’t’ work because each specimen had its small unique quirks.

Thanks once again :)