Hi, thanks for composing such a thorough reply and mentioning specific examples. I guess this site seems to focus on getting an identification to species level, but I have come to realize, that different varieties (or subspecies) of a species are very much different plants, when the taxonomy work is solid. So, I understand what you are saying, that until a plant is identified to something that exists in the Jepson eFlora key (for example), it is unresolved.
When you say a plant can’t be identified, what do you mean by this? It is impossible even with good photos? Of course most people are not botanists, and probably don’t realize infrataxa can be important. Once we get to know the plants in our area of focus, this becomes more apparent. I have learned more, and I agree, trying to use the key is helpful.
I’ve seen a lot of Lupinus misidentified, and I won’t be able to find the time to look at all of them. Especially Lupinus nanus vs. L. bicolor. In a photo, it can be hard to see the scale or depth. In person, of course we would have no problem at all. So bringing your eFlora on your phone, or saved as a pdf, is helpful to learn. In other words, try to key things in the field, if possible.
Of course, as you said, some taxa are not accepted by Jepson, but can be used here on iNaturalist. I have found this to be true for Malacothamnus species. These are under study, and there are draft keys, but the current Jepson eFlora key is problematic. When Keir Morse is done with his work, we will have a much better described Genus. The thing about taxonomy is sometimes people inappropriately either split or combined species within a Genus, for lack of better understanding. Much work needs to be done, of course.
So for Malacothamnus, I can use my local Flora that was published in 1970, and get the same answer as Keir Morse, but if I used to Jepson eFlora, I would not find certain species listed. So even authorities are not perfect. The name I pick for the Latin binomial can be subjective, in this regard. My friend likes to add the var. maritima to Eschscholzia californica where appropriate, even though it is no longer accepted by Jepson. While this variety is no longer accepted, it certainly is apparently something different. Perhaps it is more a form, who knows, but it is different. iNaturalist allows these old varieties.
The unabridged note for Rhamnus crocea says that the infrataxa are no longer used, correct? What are you showing us with this link, that we should be aware the Genus and species need more study to resolve what is or is not a species within the Genus? There are intermediaries between the R. crocea and R. insula, it says. The subspecies of R. crocea were considered conspecific by C.B. Wolf in 1938?
Brodiaea are also in need of study. Some populations have been studied and adjusted to be within certain taxa, but more study is needed. I’m suspicious that some could be considered conspecific like B. jolonensis and B. terrestris subsp. kernensis. The problem is study is needed of all the populations of these, and possibly also B. coronaria all at once to compare.
Back to Rhamnus crocea, I do see a lot of variation in the leaf size and color. I was wondering if there were different varieties, but I thought perhaps they must just vary depending on the phenotype and since I see small leaved and large leaved plants side by side, I guess they simply can vary. I would hesitate to even assign the word form to any of them.