The Little Oak That Shouldn't

We are told that North American oaks can be divided into two sections: Red/black, whose acorns mature in 2 years, and white oak, whose acorns mature in 1 year. And we are told that never the twain shall meet.

We are also told, in Oaks of North America, that live oaks - evergreen oaks - can have characteristics from both groups, but are grouped with in red/black section.

Nice, clean and tidy, right?  How, then, do we explain Q. x tharpii (Tharp's oak)?

Before I go any farther, I should explain my latest project.  Here's how a real oak geek spends his time: I have been going through Oaks of North America and recording every hybrid oak given and which section the two parent trees come from.  Geez, it sounds even more pathetic when I write it than it seemed when I was actually doing it.

Tharp's oak is Quercus emoryi X Quercus graciliformis - Emory oak crossed with an oak variously known as chisos oak, slender oak or graceful oak - meaning that Q. graciliformis has one common name for every individual in its 2 square block range.

Emory oak:  Deciduous.  White oak.  Acorns mature in one year.

Chisos/slender/graceful oak:  Partly evergreen (I guess that makes it "mostly deciduous").  Does that make it partly live oak?  Acorns mature in two years.

I have always said that there is one oak species with hundreds of varieties (making me the ulimate "lumper"), but lately I have been willing to concede that perhaps the sections of oak might form 4 species whose boundaries are not crossed in the wild.

I am back to the whole one species thing.