if I buy a CD with the cash in my Roth account, does the interest I earn count toward the $4500 limit?

The interest your earn on a CD in a Roth account doesn't count toward the tax-free interest limit because it isn't taxable.

is one taxed unmercifully on the cash earned from a CD?

CD interest earned in a Roth is never taxed if you follow the guidelines for tax-free withdrawals. CD interest in a Traditional or Rollover IRA isn't taxed until you start withdrawals from the account. CD interest in a taxable account is taxable at one's marginal rate (mercy!) at the end f the quarter in which it is earned.

I wrote a question about CDs last week but it has disappeared altogether!

It was posted on a different board.