Phytokeys (1.39) and Phytotaxa (1.185) have an IF not so high as Taxon, but are some of the best journals publishing taxonomy. Phytokeys is open access and the publishing fees are afordable, review process is really quick. Phytotaxa also accepts free-of-charge ms. but then the ms. is not open access.
I recommend some: Taxon, Systematic Botany, Phytotaxa, Phytokeys, Plant Systematics and Evolution, The Journal of the Torrey Botanical Society, etc. Obviously, first of all you must be sure if your manuscript is within the scope of these Journals.
Someone affirms that Journals with high impact factor are always the best: I think that the metrics is frequently misleading, and often does not justice to the real value, even historical and cultural, of the Journal. Everybody knows that IF is only a strategy for careers based frequently on papers with more than 10, 20, 30 Authors. What about eminent botanists of the past who currently would not have credit only for not having published with a high IF?I suggest the following recent book about "metrics" including its impact on the Academic World. Enjoy it:
I totally disagree with Alessio. The only requirement of Taxon is originality of the work. If the work is deserving the reviewers, editor and production editor will improve the MS. The authors need not to be Shakespeare so far as the English language is concerned.
The problem with Taxon is that if you are not carrying out studies at whole family or at least genus level, it is very unlikely that the paper will be sent out for review!