(ABT 1517-ABT 1573)
+---Thomas Trethewy (-ABT 1616)
+---Bartholomew Trethewy
+---Bartholomew Trethewy (-1666)
+---Bartholomew Trethewy
+---Thomas Trethewy (ABT 1675-MAY 1743)
| +---Jane Bruart 
+---William Trethewy (ABT 1712-JAN 1777)
| | +---Phillip Mellow (ABT 1660-JAN 1711)
| +---Joan Mellow (ABT 1680-)
| +---Jane ?
+---John Trethewy (ABT 1741-)
| +---Grace Rickard
+---John Trethewy (ABT 1776-)
| | +---Francis Honey
| +---Elizabeth Honey (ABT 1742-)
| +---Ann Johns
+---Thomas Trethewy (ABT 1805-1884)
| | +---William Gummow
| +---Mary Gummow (ABT 1776-)
| +---Mary Colman
+---John Trethewey (ABT 1849-06 MAR 1924)
| | +---Robert Tippett
| +---Ann Tippett (ABT 1816-BEF 1871)
| +---Ann Solomon
+---William James Trethewy (ABT 1885-)
| +---Eliza Keast (ABT 1851-29 MAR 1921)
+---William Douglas Trethewy (19 DEC 1919-19 JAN 1987)
| | +---John Hooper
| +---Phillis Annie Hooper (07 JUL 1885-09 APR 1962)
Paul James Trethewy (23 OCT 1957-)
+---Barbara May Byatt