+---Richard Trethewy (ABT 1665-JAN 1741)
+---John Trethewey (ABT 1690-)
| +---Ann Martyn 
(ABT 1666-JUN 1738)
+---Joseph Trethewy (ABT 1735-DEC 1816)
| | +---Phillip Mellow (ABT 1660-JAN 1711)
| +---Temperance Mellow (ABT 1690-MAY 1765)
| +---Jane ?
+---John Trethewey (ABT 1764-JAN 1834)
| | +---John Rickard
| | +---Jonas Rickard (ABT 1705-)
| +---Caroline Rickard (ABT 1734-)
| +---Honour ?
+---Benjamin Trethewey (ABT 1802-BEF 1861)
| +---Charity Strangeman (1756-)
+---James Jabez Trethewey (23 NOV 1847-23 APR 1924)
| | +---Richard Thomas (ABT 1763-)
| +---Elizabeth Thomas (ABT 1808-)
| +---Mary ?
+---Ben Clifford Trethewey (31 MAR 1875-31 AUG 1913)
| | +---William Trebilcock
| +---Susan Trebilcock (ABT 1848-02 JUN 1907)
+---Willis James Trethewey (08 OCT 1902-07 JAN 1961)
| +---Polly Brooks (ABT 1882-)
Ben Clifford Trethewey (10 DEC 1930-)
+---Celina Fournier