Add ranks for plant hybrids to taxonRank vocabulary

[qgroom]

The vocabulary for taxonRank lacks ranks for plant hybrids.
i.e. nothofamily, nothosubfamily, nothotribe, nothosubtribe, nothogenus, nothosubgenus, nothospecies, nothosubspecies

However, these are valid rank terms for plant hybrids as stated in the International Code of Nomenclature for algae, fungi, and plants article H.3.1

[mdoering]

Indeed. And I agree we should allow them to be shared as such.

Both the GBIF & COL API separate those values into 2 values, the rank without notho and a separate notho field which represents the part of the name which is prefixed by the x. See also tdwg/dwc#43 and a COL API example: http://api.catalogueoflife.org/dataset/3LR/taxon/94NJ

With that model both APIs rank enumeration should not contain the notho values above.

[qgroom]

@mdoering So the notho field is in effect a hybrid flag, at least for plants, fungi and algae.
What is the advantage of this rather than treating these as additional rank terms?

I should have mentioned that this DwC issue is also raised. tdwg/dwc#390

[mdoering]

One advantage is that we can compare ranks more easily. One goal of our rank enumeration is to provide a native ordering. With "duplicates" like species and nothospecies this becomes tricky.

Also the notho field tells us where to place the hybrid marker. If I remember the code correctly you either specify a notho rank marker OR use the hybrid marker, but never both. They are equivalent.

Foo bar nothovar. baz = Foo bar var. × baz if I am not mistaken.