This is a little unanswerable in the same way questions about how many languages there are are unanswerable. The way taxonomists decide what makes two different patterns of life separate species varies drastically across for example plants and animals (fungi are especially messy). Different standards are used even within botanical taxonomy across different families. Even measures of phylogenetic differences have big limitations and are applied differently

Also to touch just a tiny bit on just how messy this question can get with fungi:

If you take certain species of fungi, put them in some soil they're really not adapted for, they will literally increase the rates of horizontal gene transfer and start borrowing genes from soil bacteria there in order to quickly evolve themselves and better adapt to that soil

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5095653/

Certain parasitic plants may act similarly:

https://www.pnas.org/content/113/45/E7010

thank you; i learned from your comment which is great