Texas species of Dandelion, as near as I can tell

According to Flora of North America, there are two species of Dandelion (Taraxacum) in Texas: T. officinale and T. erythrospermum. Apparently, the only way to tell the two apart is by the color of the achenes. Taraxacum officinale has fruits that are "straw-colored to olive, brown, or red to pale or dark gray" while T. erythrospermum has fruits that are "brick red to reddish brown or reddish purple". What follows are some photos of what I believe are representative of both species.

Taraxacum officinale at left, Taraxacum erythrospermum at right.

Fruits in greater detail:
Taraxacum officinale:


Taraxacum erythrospermum:

I have always been dubious of colors as key characteristics and learned early on not to trust them. I have since learned there are some circumstances, but I remain dubious here. At the very least, it seems like there might be some structural characteristics here that would be much more stable that could be relied upon. In the previous photos, T. erythrospermum seems to be smaller on average (this was the largest achene I could find from the specimens I took), be less hairy, and be muricate throughout (the rough horn-like projections). Taraxacum officinale, on the other hand, seems to have minute hairs (contrary to the description) and be muricate only towards the apical end. There is also, of course, a color difference. In the plants themselves, T. officinale has a tendency to have harier peduncles in the environment these were encountered in.

This is admittedly a very small sample size and I will try to follow-up with more info. Ideally, I would grow the two species and see how well they retain their parents' tendencies. Color is usually such an unstable characteristic that I'm still not convinced (as is leaf shape, the other characteristics used). Not only that but there is overlap in the description itself.

Another good, and more striking, comparison photo of the two can be found from Maryland Biodiversity Project and is displayed below:

I tend to think this comparison represents the extreme end of the variability of the two species and identification of other individuals is not usually this easy.

Observations the photos are found in are as follows:
Taraxacum officinale:
Fruiting head. Single achene.
Taraxacum erythrospermum:
Fruiting head. Single achene.

Reliable T. erythrospermum observations:
https://www.inaturalist.org/observations/7811183
https://www.inaturalist.org/observations/7766362
https://www.inaturalist.org/observations/7731039
Reliable T. officinale observations:
https://www.inaturalist.org/observations/9577717
https://www.inaturalist.org/observations/9402362
https://www.inaturalist.org/observations/9292763
https://www.inaturalist.org/observations/9244265
https://www.inaturalist.org/observations/9166812
https://www.inaturalist.org/observations/9064497

UPDATED 2 MARCH 2021

Further investigation reveals that the situation presented above is significantly oversimplified. For details, read the comments. This update is intended to include some of the main points to encourage further reading.

1. How many species occur in Texas?
   It's likely that no one knows. It's clear that at least three species occur here: T. officinale, T. erythrospermum*, and a species no one really knows the name to (to be clear, that doesn't mean it's a new species, just that no one knows the taxonomy well enough to know).
   
   *The plants found in the US that go by T. erythrospermum may correspond to what is known as section Erythrospermum in Europe. Given this, T. erythrospermum could represent one or many different species and, even if there is only one species, it might represent a species other than T. erythrospermum. As such, I will use T. cf. erythrospermum in the other sections below.

2. Calyculi and phyllaries
   The phyllaries are the sepal like structures that surround the florets in bud. The calyculi are the bracts at the very base of the phyllaries that typically spread outwards. It turns out that the calyculi of T. officinale are broader than those of T. cf. erythrospermum. Observations illustrating this difference can be found here:
   https://www.inaturalist.org/observations/21613885
   https://www.inaturalist.org/observations/21613871
   Other characteristics of the phyllaries and calyculi are important (as shown here), but the reader is directed to the comments for details.

3. Best practices on iNaturalist for Texas
   These are my general recommendations at this point in time.
   
   Identification
   3a. Understand that the taxonomy is poorly understood and be open to the possibility that it could change for the better without you knowing. Getting into an argument over taxonomy here is probably pointless unless you really do spend a lot of time researching the taxonomy (in which case, please write your own post so I can read it!). Even a citation battle, which I would generally encourage, might prove unfruitful here if using only sources from North America.
   3b. If you feel comfortable with it, use T. erythrospermum and T. officinale if there is enough to separate them into there respective groups as provided here. Unless some better taxonomic treatments are provided, using this potentially flawed taxonomy is probably better than nothing or the general research grading of all as T. officinale.
   3c. When in doubt, just keep it at genus and understand that this will likely represent the majority of observations. This is generally a good practice if you don't want to wander down a rabbit hole.
   Observing
   3d. Understand that your observation probably isn't identifiable to species with any certainty at this time and especially not if you don't take time to get the proper structures.
   3e. Photograph the important structures in hopes that they will be identifiable when/if the mess gets sorted out. These include: achenes, receptacle, phyllaries, calyculi, peduncles, leaves, and habit. The best time to photograph phyllaries and calyculi is after the flowers finish, but before the phyllaries open to release the achenes. Try to photograph calyculi where at least one is flat and has all parts is in the same plane so that the overall shape is documented (picking and flattening is encouraged). Any bulges in calyculi or phyllaries should be visible in the photos.
   3f. If you go through the trouble of getting the photos in 3e for a lot of plants, it would be worth adding links to those observations in the comments of this post. I would create a project to make it easier but don't really have to time to manage that right now.

Posted on March 24, 2018 01:25 AM by nathantaylor