+---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
+---John Trethewy (25 DEC 1805-1871)
| +---Catherine Scholier
+---Alexander Thomas Trethewy (16 AUG 1842-09 AUG 1901)
| +---Margaret Grinton (24 APR 1810-1860)
Gladys Alma Trethewy (21 OCT 1885-)
| +---James Trethewy
| +---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)
+---Anna Maria Trethewy (-20 SEP 1900)
+---Ellen Chesley