Phytotaxa, South African Journal of Botany and Flora are very good journals for quick publication. Apart from that, you can just copy-paste your title and Abstract in the following link, it will automatically suggest you appropriate Elsevier and Springer Jornal for your Paper...
For Elsevier Journals: https://journalfinder.elsevier.com/
For Springer Journals: https://journalsuggester.springer.com/
There are many journals where you can publish papers on plant taxonomy.
If you are searching journals for easy publication, I will discourage you. They will not be good.
To publish papers in first three journals suggested by Arvind Singh is very difficult, particularly Taxon.
You can try Phytotaxa and Telopea for quick publication having good review system.
You can also think of Rheedea, Nelumbo, Plant Science Journal, Journal of the Bombay Natural History Society, Indian Journal of Forestry, Indian Forester, Journal of Economic and Taxonomic Botany, Taiwania, Journal of Japanese Botany, etc.
There are a large number of very good journals to publish taxonomy manuscripts, but this is conditional on the relevance of information in the paper. I generally choose journals that are somehow related to the content of my paper. See below some good journals:
There are so many such journals but you should choose it as per your requirement. If you paper is a path breaking research then go for Taxon. Similarly, if it is a monograph, then go for an international journal. If a new record then go for a regional journal. If you do not mind paying, go for Phytokeys. Novon publishes mainly novelties. Blumea and Garden Bulletin Singapore publishes papers dealing with Malesian Flora. Taiwania and Kew Bulletin mainly new species. Some journals have continental bias!
There are many journals which publish plant taxonomic research.
BUT randomly selected journal may not be suitable for your research paper.
Please go through each and every journal (you now already have a long list in earlier replies) to see what they are publishing. Then only one can select the suitable journal. This will also be helpful in assessing your research work.
Most of the journals charging publication fee are predatory and should not be preferred. Expert taxonomists often assess research published in predatory journals as second grade research.
Today, doing good research work is half job done only, or even become useless if not published. The second half is completed only when a good research work is published in a suitable and good journal.
So many journals are there, especially Nordic Journal of Botany, Adansonia, and Taiwania is quickly completing the review process and published within a year.
I would agree that Taxon can be slow in time to decision >6 weeks, but only basing that on one experience and in general, decision time seems to be increasing with a lot of journals at the moment.
When you choose journals, keep few things in mind:
1. Is it free to publish and free to access? Not many options, but there are indeed some.
2. If AT LEAST the journal is free to publish (not free to access), its good. Many options.
3. How many issues do they publish per year? AT LEAST four times a year is best.
4. Check how long it takes from submission to publication? Least time is best. AT LEAST three months is best.
5. Look at your paper and introspect if it is good enough to go in the highest impact factor journal? If you do not know then it is not good for you. If you know, then either improve it to fit highest impact or move down on scale to lower impact journals.
6. Do not publish in absurd journals. It is you who should be capable enough to judge which are absurd journals. Trust me there are many!! I do not want to name here.
7. Trust me, some journals accept or reject based on who the authors are. Always bring into light names of such journals and always avoid publishing in such journals.