Hey folks,

I'm thinking about redoing some hardwood floors in my house that are just plain gross. The wood is mostly in decent shape, but one of the boards has a nasty gouge/split in it. The board is about two inches wide. Here's some pictures: https://imgur.com/a/Us4HEfQ
Any advice on how best to handle this?

I don't have any replacement boards handy, and I'm not sure I'd be able to match it with anything from our local lumber stores, though I suppose the closet is an option if I needed to harvest a replacement from within the house. I'm not sure what kind of wood it is- my research suggests maple is most likely, but it's so ratty and discolored that it's hard to tell.

This is a shake board, where there is a defect in the wood grain. The best solution is to replace the board. Finding another board as replacement would be the best thing. To get a replacement you would need to measure accurately the dimensions. You need the width and thickness. If you can not find a way to find the thickness by looking at the edge of the floor at a doorway or where the heat comes through the floor you could use a drill and if you can tell when the drill changes when it erupts through the bottom of the flooring as you go through the board near the shake area.
Once you find the dimensions you can start to look for a replacement.
Trying to repair it is futile.
Even if you can not find the exact specie to replace the board you will be better off than trying to repair it.
If you could find a board in the closet, it will be the best option. You will only need to replace the part that is defective. A good floor mechanic with the right material is the best solution. Board replacement does not take very long.

Interesting, thank you for clarifying what it is. Do you have any advice for trying to figure out what kind of wood it is to find a replacement board, or how to extract a replacement from a hidden space in the closet?

Here are a few pictures of the wood in a few different contexts- with polyurethane and some number of years, some light sanding on bare (but dirty wood); and after picking away that cracked bit to see how deep it goes: https://imgur.com/a/UqORHWV

The wood may be maple, or ash or beech.
It's not easy to get replacement wood from a closet. First take off the base boards.
The row against the wall was the last one installed. It was top nailed so you ought to see the places where it was nailed. Using an eighth inch punch you can set the nails through to the sub-floor so the row will be loose. Pry up the whole last row to get at full width boards that you can use for the replacement. Pry up the next row so you can choose the board that you like. Usually the shortest boards will be installed in the closet so a good short board can be used for a partial board replacement to only remove the bad part where the shake is.. You can use a vibrating saw like a Dremel to cut out the bad part of the shake board using the new closet board as a pattern. Cut the tongue off on the replacement board. Mark the correct length on the old board then drill 5/8" holes at both ends of there the new board will go. Connect the holes with 2 rows saw-cut from each hole drilled close to the end. Pry out the loose part. Use a 1/4" chisel to clean up the removal then use pliers for taking out the fasteners.
The new board will fit into the place for it after you take the bottom of the groove off, slipping the tongue in first. You can use a good wood floor glue to hold it down using some weight to hold it till the glue sets.
You will need to figure how to repair the closet.
A floor mechanic can do the job, too.

Very detailed, I'll look into the feasibility of doing this in my house tonight. I'm a woodworker and I've got a bunch of maple laying around, so I can replace whatever I take in the closet with a board that probably doesn't match very well.