I'm a little surprised to see the knot at the one end...
I know it's "only secondary wood" as the cabinet makers refer to it, but Poplar or pine were common... no need to use a knotty-bit ?
At any rate, it looks like four separate boards, jointed and edge-glues together to make the wide plank. Also looks like flat-sawn lumber, as opposed to quarter-sawn.
Poplar is still common, and easily worked... or, if you want to make life easy for yourself, get some furniture-grade hard-wood plywood of the appropriate thickness, stain it, and make your bottom board from that, and store the original in a safe place, to "go with the machine" when you are ready to part with it. ( staple an index card to it with the machine, model, and serial # ).
