I've read a published county history for Monroe County, Indiana that included a sketch about William Thomas Harden, b. 1839, IN, d. 1927, Monroe County, IN. One of his brothers, David R. Harden, was b. abt 1834, in TN, and married my 2nd great-grandmother, Martha Jane Carmichael, in 1879, Greene County, IN (records indicate she was his 3rd wife). These Harden men's mother was identified as Elizabeth Ragan Harden, b. abt 1809, NC. Her husband was William Harden, b. abt 1809, NC. The Harden name has been spelled Harden, Hardin, and Harding in various records.
I've not found any records for Elizabeth that indicates a maiden name other than this history sketch, so don't know whether it is correct or not. David was the oldest known child I've found for this couple so have wondered if the "R" was for his mother's maiden name. It's all speculation on my part, however, at this point until I can find some records to support it.