Can my 90 year old dad sell land to my daughter if my mom is on Medicaid? Any penalties? Does it have to be market value? Land is in his name.

No, quite honestly he cannot, not just because of his wife but because of himself. Any sales would need to be fair market or would be "gifting". You can look up rules around that yourself.
He would need to see an elder law attorney for options he has.
When you start messing with this you are talking division of property done legally, who is on deeds and what your state community property laws are as well as the assets of a couple and how they are help. If Mom is already on Medicaid there are some there who know something and who found out how to do this, so the research then continues on what can be done and what cannot be done.

I would say do your own legal research.
Don't count on a Forum to answer legal, medical, financial questions; for those you need expert advise. We are great with what deoderizer to buy or what to tell Aunt Irma about Christmas plans. But when you need solid advice and cannot afford to go wrong you need an expert.
Good luck.

If it gets sold then your Mom may lose her Medicaid qualification until those funds are spent down.

he can sell if it’s market value, not less. Gifting is not allowed.