One Species... Drat!

We are told that there is a clear line of demarcation between oaks of the white oak group (acorns mature in 1 year) and oaks of the red/black oak group (acorns mature in 2 years), and never the twain shall meet. White oaks have rounded lobes, and red oaks have barbed lobes. Easy, right?

I spent a recent plane trip scouring Oaks of North America in hopes of finding crosses between oaks of the white oak group with oaks of the red oak group. Because I am a dork.

I thought I had found 2 examples:

Quercus tharpii (graciliformis x emoryi)
Graciliformis, chisos oak, a card-carrying red oak group member with barbed lobes and acorns that take 2 years to mature.
Emoryi, Emory oak, with acorns that mature in 1 year.

Eureka!
Not so fast. Emery oak has barbed lobes, and despite having acorns that mature in 1 year it is generally considered to be a red oak.
Doh.

Quercus inconstans Palmer (gravesii x hypoluecoides)
Gravesii, Chisos red oak or Graves oak, with acorns that mature in 1 year.
Hypoluecoides, silverleaf oak, with acorns that mature in 2 years.

Double Eureka!
Not so fast again. Apparently there is either doubt or inconsistency about the length of acorn maturity in both cases. In the case of Graves oak, Oaks of North America says 1 year but adds paranthetically "(may take two according to C.H. Muller)."

In the case of silverleaf oak, Oaks of N.A. seems adament that acorn maturity is 2 years, but this Texas A&M site says: "The acorns can mature in either one or two years, even though it is a member of the black oak group, whose acorns usually take two years to mature."

The Texas A&M site classifies Graves oak as a black oak, but mysteriously leaves silverleaf oak unclassified with respect to group. Does it have rounded or barbed lobes? Yes. Yes it does. Except for when the leaves are entire, which is most of the time.

Why would a species have acorns that can take either one or two years to mature? Might it not be a hybrid that crossed that supposedly uncrossable white oak / black oak divide? Does anyone know anything about these hybrids?

More taxonomic fun to come!