(-JUL 1733)
+---Richard Trethewy (ABT 1720-)
| +---Isabel Beaubery 
(-FEB 1732)
+---Robert Trethewy (ABT 1759-)
| +---Ann Jewell
+---Robert Trethewy (ABT 1802-BEF 1861)
| +---Elizabeth Sarah
+---John Trethewy (ABT 1837-)
| | +---William Trevithick
| +---Mary Ann Trevithick (ABT 1808-1877)
| +---Elizabeth Harry
Mary Trethewy (ABT 1879-)
+---Eliza Plummer (ABT 1844-)