Taraxacum (the genus of dandelions) receives little attention from taxonomists because it’s so bewilderingly complicated and because morphotypes often correspond to clonal lineages that are supposedly incapable of sexual reproduction. Clonal in the sense of their seeds being in a sense just outgrowths of the mother plant, no pollen involved in their production. The asexual species are often dismissed as “merely microspecies”. But in order to devise a taxonomic model that actually works, the asexual lineages have to be treated as species having the same taxonomic status as the sexual ones. Otherwise, none of the taxonomy could make any sense. There are over two thousand of these asexual species, with more being discovered and added every year, and trying to fit them into their sexual species of origin would make all of the species un-identifiable and undefined. It isn’t impossible to figure out the biology of these beings, to identify them as morphospecies, and to apply the taxonomic names correctly (or at least consistently). But it isn’t easy.
Here are some pairs of dandelion species from here at Edgewood, with taraxacological commentary. For ten years I have been studying these species and the rest of the array of species that occur here at Edgewood. And for ten years I have studied the dandelions of northwestern North America, both the native and non-native species. All of these are treated in most floras as “Taraxacum officinale” (a name that is essentially meaningless). I know of most of these from other localities in the Clearwater Valley or beyond. Some are very common and widespread, others less so. And they are all introduced from Europe. Our native dandelions are not close relatives and are not similar to these.
Above are two similar species. The one on the left has shorter and less pigmented petioles, and darker involucres with the outer bracts more tightly recurved. Both lack pollen, but the one on the left has somewhat paler stigmas. Both belong in section Borea. I believe the one on the left is T. brachycephalum and the one on the right T. praecox, but it is difficult to find reasons to be confident about applying names to most of the species of section Borea. They are native only in northern Europe, but a large portion of them have shown up in North America as common introductions, especially in Canada and the northern tier of the US. Comprehensive identification keys to section Borea are lacking, even in Europe. Identifications must rely on comparing each specimen to the type specimen of each species. Types are the specimens that define a species. In a sense, only the type is the species; all else is only comparison.
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Above are two more species superficially similar to each other, both with complexly lobed leaves having the “shredded” look. The one on the left has longer, more pigmented petioles, somewhat paler leaves with a broader terminal lobe. Also, the left one has pollen, the right one does not. The leaf distinctions aren’t easy to see in the above photo, so in the photo below are leaves isolated from the plants and set so that the four on the left are from the left plant and the five on the right are from the right plant. The left plant is section Taraxacum, and is, I believe, T. fagerstroemii, and the right plant is section Borea and is, I believe, T. expandens.
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Two squat little species of section Borea with enlarged terminal lobes on the later-forming leaves. Distinctions: the one on the left is stiffer and darker overall, with richer purple pigmentation in the petioles and outer bracts, and with on average more lateral leaf lobes. Plus left has a bit of pollen and dark stigmas, right has no pollen and yellow stigmas. Left is T. boreum (the type species of section Borea), and the one on the right I will tentatively name as T. laceratum, though I am used to larger representatives of that species than these runty little plants.
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Both of the species below have more or less erect leaves with enlarge terminal lobes, the species on the left has somewhat broader petioles than the one on the right, and its scapes are not much longer than the leaves. Also, left has leaves with on average a smaller terminal lobe, and though the photo doesn’t make it clear, the leaves on left are glossier and less hairy. Also, left has recurved bracts that are more tapered while right has reflexed bracts that are of almost even width to near their ends (see second photo). In the third photo, the greater number (on average) of leaf lateral lobes and the relative slenderness of those lobes on the left species is apparent (the six leaves on the left), as are the characteristic pairs of opposite teeth a bit above the midpoint of the leaf terminal lobe on the right species (the six leaves on the right). Left: section Borea, tentatively named as T. biformatum; right: section Taraxacum, T. retroflexum.
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In the following photo, both plants lack pollen and are of section Borea. The left plant has petioles with broad green wings and little pigmentation. Otherwise similar. Left is, I think, T. poecilostictum and right is, I think, T. prasinescens.
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Two large species with pale petioles. Left has exserted stigmas and larger capitula which (on sunnier days than today) open so widely that the top is domed and the outermost florets somewhat reflexed. Left has messy-looking outer bracts, which twist and bend this way and that (second photo), while the outer bracts on right are tidily, regularly recurved (third photo). Left has pollen and lighter coloured stigmas; right has no pollen and dark stigmas. Also, left has more leaf lateral lobes, many of which have an abruptly upflipped terminal portion (fourth photo, leaves on the left). Right has distinctly larger terminal lobes and the leaves are dull and with a characteristic rubbery texture. I believe left is T. ingens (section Taraxacum). I’ve never been able to get right identified, so I just know of it as “rubbery” (one of the large species of section Borea).
