Either stop using genera to measure diversity although it is not clear what the alternative is
Easy: the Phylogenetic Diversity Index (Faith 1992, 1994). Requires a phylogeny, but no genus or even species assignments. I'll look up the full citations and abstracts 1 or 2 days from now.
There not being a definition for "genus", genera are not countable. People must stop using them (let alone families or orders!) as a pretend measure of biodiversity. Period. Full stop.
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This was also in your last e-mail. It's very strange. So far, I've only seen spammers assume that if you write HTML code into an e-mail, it will be in HTML as opposed to plain text; and what's more, there's no other HTML code in your e-mails.