+---Richard Trethewy (ABT 1665-JAN 1741)
+---William Trethewy (ABT 1694-)
| +---Ann Martyn 
(ABT 1666-JUN 1738)
+---James Trethewy (ABT 1719-)
| +---Jenefer Sweet (-SEP 1733)
+---William Trethewy (ABT 1753-)
| +---Grace Warne
+---Richard Trethewy (02 FEB 1799-24 DEC 1875)
| +---Catherine Scholier
+---John Trethewy (25 JUL 1823-24 SEP 1876)
| +---Catherine Hooper (25 MAR 1796-06 DEC 1893)
+---Josiah R Trethewy (27 MAY 1867-14 OCT 1964)
| +---Margaret Eleanor Ross
Margaret R Trethewy (13 DEC 1902-27 MAR 1978)
+---Rosa Ethel Buker (19 DEC 1872-29 OCT 1951)