I guess my first comment is: it is not available anymore, which makes me worried about the longevity of this as specific clearly identified Agave. I think both nurseries are reputable places that are relatively careful with plant IDs and plant info, but on the other hand PDN is pretty quick to slap names on things as an obvious marketing strategy. Nothing wrong with that, but one can wonder how to propagate that into a plant database. I guess it is a hybrid so the strict 'it has to be on CoL' rule may not need to be followed, but accepting this particular named selection into the database brings up the issue what to do with images of these kind of hybrids from the wild (see below).
2nd: Since it was seed of something that was considered a hybrid, what was the seed: a backcrossed hybrid or a lucky hybrid x the same hybrid, but that is still not expected to produce true. Had this been an offset and then propagated through tissue culture it seems one could have been much more confident in the plant being what it is purported to be, but it goes back to the question under the first comment above: it has been named based on this specific seed grown batch, so how do we handle plants not specifically from this seed batch, another category?
3rd: I guess another question is: is there an official description somewhere to make it something that can be considered a true recognized hybrid like for example Agave x murpheyi or are we going to accept this nursery coined (PDN most likely) plant as something that enough people have growing that we can get some good pictures in the database and is there enough of a population that this plant through offsets or more seedlings will become available again. The problem is that wild collecting of plants in AZ is not allowed, so it would always have to be seed or offsets from cultivated plants and hybrid seed is frequently not going to be the same as the parent.
I have a buddy who has spent a lot of time up there specifically looking at the Agave populations and their relationship to the native people who lived here before us (I will post a link to a forthcoming book when it comes out) and he feels that there is so much variety up there that it can be hard to know when what becomes what. Lots of hybrids, lots of possible domesticate agaves that have not yet been recognized/described and lots of intergrades making a clear distinction between species difficult. However he has seen a lot of these:
http://www.agaveville.org/view...
I think he would hesitate to identify the A. parryi positively as Agave parryi var. couesii, mainly because the distinction between the different parryi varieties within Arizona is quite difficult as the transition from parryi var. parryi to parryi var. couesii is also not sharp at all. His opinion of these hybrids is that if it leans too much towards parryi, it is not really that interesting as an Agave. The chrysantha leaning ones are particularly fierce and ferocious with regards to teeth and appearance.
To me Agave x parryantha is a poor name, also unlikely to ever be an official name. I guess Agave hybrid 'Yavapai County' is something that could be worthwhile as a database entry, but what if someone has a picture of an Agave parryi x Agave chrysantha and not a direct clone (offset) from Agave hybrid 'Yavapai County'? Should those be considered the same plant or different? I guess if we are strict they'd be different, but that assumes we know what Agave hybrid 'Yavapai County' looks like and how consistent a seed grown batch of plants can be and in addition how it would differ from Agave parryi x Agave chrysantha - to me they are most likely the same. That is my problem with these nursery introductions - people can buy them, but once you start digging the info about them is often sparse and uncertain and the specific reason for naming them especially with a cultivar name like Yavapai County complicates matters with similar/the same hybrids not directly related to the named plant.
Since it lacks an official description it is unlikely to ever find its way on the CoL, but it might be found in the trade...
Another thing to consider is that there is an officially described domesticate Agave from the same general region that is called Agave yavapaiensis, which has affinity with A. chrysantha, but is suggested to possibly have a relationship with Agave shrevei, which is hypothesized to have been brought up from Mexico by the native people in trade. This is of course an obvious source of confusion.
So I guess in summary: yes the description on the nursery pages is probably valid, to at least identify this plant as a hybrid between Agave parryi and Agave chrysantha, or some iteration/back cross thereof, for entry into the database. If we had to name it beyond that I'd feel more comfortable with 'Yavapai County' over x parryantha, which just feels wrong to me, it is something you see more on the PDN website and most Agave taxonomists I know really do not like it, and I get that. However naming it A. hybrid 'Yavapai County' means it probably has to be distinct from Agave parryi x Agave chrysantha, though in all likelihood it falls within the same group of hybrid Agaves as shown on Agaveville.org, but once it has a cultivar name (though in this case that is wrong too because these plants were seed grown, not propagated by clonal offsets/tissue culture) it is considered distinct from any other plants of the same origin but not directly propagated from the named plant.
Maybe more than you asked for but this is my 2 cents worth (though, its probably a little more than 2 cents...
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Maybe it's best to hold back on this entry, then.
