Width would be an issue.
Let's see if I can explain this.
Trees are living, breathing things. They contain water.
When trees are cut down they begin to dry out.
As they dry out, they shrink. Some more than others'
But they all have some basic guidelines for shrinkage.

Logs have growth rings. And shrinkage is measured
in relation to those growth rings.
Growth rings form (almost) concentric circles.
Logs tend to shrink about twice as much tangentially
as they do radially. Here is a picture.

{{!gwi}}

As you can see, since the rate of shrinkage is not the same,
cracks form, called checking in lumber. This can be mostly
prevented by milling the logs quickly after felling them.
Milling the logs changes the internal stresses affecting the logs.

Logs are milled (sawn) in 3 different ways.
Each method has its own benefits and disavantages.

First is the most common way: flat sawn lumber.
Logs are just sliced into lumber regardless of grain direction.

{{!gwi}}

Lumber sawn using this method tends to contain growth rings
that orient in both directions. Drying causes cupping.
Cupping occurs as the growth rings try to straighten out.
So cupping occurs in the opposite direction of the growth rings.

Next we have quarter sawn lumber.
There are several different methods of quarter sawing.
All of which are meant to get the highest quality lumber
with the least amount of waist. Quarter sawn lumber tends
to come in narrower widths to avoid flat sawn growth rings.

{{!gwi}}

Then we have a rare form of milling known as rift sawing.
Rift sawn lumber is cut so that all the growth rings are
perpendicular to the wide dimension of the lumber.
As you can see this method produces a huge amount of waste.
But it also makes for exceptionally stable lumber.

{{!gwi}}

What I have given you here could be construed as sweeping
generalities. Someone else can give you specific shrinkage
rates for a species of wood from the Wood Handbook.
But hopefully this does explain wood shrinkage.

My apologies to dial up users for the long download of pictures.

Pooh Bear

Wow Pooh Bear! Thank you for the detailed but very clear explanation. So, bottom line, does it make more sense to get the more stable wood in a kitchen so dirt and grime won't make it's way into any potential grooves betweenthe boards?

-Margie

See chapter 3.
There are even tables that allow comparisons between different species.

Here is a link that might be useful: Wood Handbook

Dirt will get in anyway no matter how you saw it.
It still expands and contracts with changes in humidity.
This problem can be alleviated by allowing the wood to stay in
the house for a few weeks and acclimate to the humidity levels.

The major goal is to prevent cupping and warping, and checking.
You minimize this by using narrower quartersawn lumber.
Less growth rings per piece means less chance of problems.

Pooh Bear

-I have seen furniture made from hickory that has lasted over 100 years, and is still in good condition. However, I have never seen a floor made from hickory, so I can't recommend the use of this species for flooring. My best guess is that it would perform similar to oak in this application, & I have never seen an oak floor with wide boards. The oak floors in our house, built in 1938, have boards that are 2.25 inches wide.

I installed a hickory floor using 5-7" planks, no tung & groove just butted them up and screwed them down. I noticed a little movement however unless you are watching carefully it would not be noticeable to anyone other than a real flooring guy probably. A T&G might react a little different but I doubt it. I would consider sealing the bottom side as that may help in reducing movement I think. It was a great looking floor. Think I used a fruitwood stain. I later made my cabinets out of hickory and used a whitewash stain on them. I believe "ericwi" is correct, the movement will be about the same as oak. So if that is what you want, I say get er done!!

Wood Handbook, Table 3-5
Hickory has radial of 7.0-7.7, tangential of 10.5-12.6, and volumetric 16.7-19.2 (depends on the exact species).
Red Oak is 4.0-5.0 radial, 8.6-11.3 tangential, and 13.7-18.9 volumetric (again depending on the exact species).
Quarter sawed wood exhibits radial shrinkage in width and tangential shrinkage in thickness.
Flat sawed wood has tangential in width and rail in thickness.
Everything in between these two extremes has a mix depending on the grain angle to the width of the board.

While hickory will move more than red oak in radial, the other numbers have a decent overlap and use for flooring should be fine.
Wider planks always show more movement then narrow planks.
If T&G flooring is used the movement occurs on each board, and they move separately. The gaps between every pair of boards widen and narrow as the seasons (and the overall humidity) changes.
Remember, only one edge of a T&G board is actually fastened. The other edge (groove) is held in place only by the tongue of the adjacent board.

The numbers are from green to oven dry, so the actual movement in use is much less, but the ratios still apply (if the wet-to-dry is twice as much the movement under like conditions for a smaller change will be twice as much).
If you want to explore the actual changes you can estimate the humidity in the house from winter to summer and the equations are in Chapter 3.

Thanks everyone. The wood I'm using will be tongue in groove and I'm leaning toward quartersawn something or other. Apparently quartersawn hickory is not readily available. Right now I have samples of Quaartersawn red oak with mineral streaks (very interesting looking), sepele mahogany, cumaru, and plain sawn blak walnut and hickory. They are each beautiful.

Brikeyee, I'm going to have to come back in the morning to reread your post...too technical for this time of night.

Thank you all. I've learned a ton!

-Margie