David - I have done some more searching and I think I can now identify Richard Rowe.
In 1841 Jane was obviously widowed and living with some of her children at Mulfra.
1841 Census
Mulfra, Madron
William RAW, 20, farmer, in County
Jane do., 50, in County
James do., 15, in County
Elizabeth do., 15, in County
Charles MATHEWS, 13, M.S., in County
1851 Census
Mulfra, Madron
James ROWE, head, unm, 29, farmer of 20 acres, Madron
Jane do., mother, wid., 63, Annuitant, Madron
Richard do., nephew, unm., 14, Ag Lab, Madron
Elizabeth JAMES, servant, unm., 19, Gen Serv, Madron
1861 Census
Tredinnack Moor, Gulval
Jane ROWE, head, wid., 73, house keeper, Madron
James do., son, unm., 39, Farm Labr., Madron
Sometime after 1861 Jane and James seem to have relocated again. I have not yet found James after 1861 but:-
Jane Rowe of Bosauljack age 78(?) was buried 30th September 1865 at Madron
(There is an ink blot over the second digit of her age but it does look like it could be an '8' which would be consistent with her birth in 1787)
Returning to the 1841 Census when Jane/Jenifer was already a widow narrows down the time we need to look for a burial for Richard which should then hopefully identify him.
And the only possibility I can find that is consistent with all the evidence is:-
Richard Rowe of Madron age 52 buried 4th November 1832 at Gulval
Richard must therefore have been the son of Richard Row and Cordelia Uren and was baptised at Madron 2nd April 1780.
It should also be noted that one of the witnesses to the marriage of Richard Rowe and Jenifer White was a John Grenfell whose signiature bears an extremely close resemblance to that of the John Grenfell who married Margaret Rowe at Madron 5th April 1800.
John Grenfell therefore was the brother-in-law of Richard Rowe.
I am reasonably confident that this problem is now solved!
CT