men at the bottom of the chart can be dated from their cited spouses. Gwrgan ap Ithel married a daughter of Cynfyn ap
Gwerystan  (that lady was a full sister of Bleddyn ap Cynfyn). Such a daughter would have been born c. 1026.
Iestyn married Constance Wen ferch Cadwgan ap Elystan Glodrydd , a lady born c. 1050. Thus we have a full generation
missing in our chart, between Morgan of c. 885 and Gwrgan of 1015.
We suggest two possibilities
for identifying the missing generation:
1. The 975 entry
in Annales Cambriae, and the corresponding entry in 2 of the 3 versions of the Brut, say that an "Idwallon ap Owain" died.
Thomas Jones, who edited all 3 modern versions of the Brut, suggests the entry was intended to be the obit of a Strathclyde
ruler named Domnall ap Eogain.  Both the Irish Annals of Ulster and Annals of Tigernach cite the death of such a
man in 975. While Domnall is alternately spelled as "Dunwallon" and Eogain has the Welsh spelling "Owain", Jones assumes
the Brut spelling "Idwallon" was an error for "Dunwallon". However, the 975 Brut entry also says that Dunwallon of Strathclyde
died that year (in addition to Idwallon ap Owain). Perhaps two men died that year, one of them being Idwallon ap Owain
ap Morgan Mawr, and that "Owain" is the missing generation in our chart...belonging between Idwallon and Morgan Mawr.
However, our dating of Ithel ap Idwallon to c. 980 makes this solution doubtful.
2. Morgan Mawr,
also called Morgan Hen, is usually identified with the man mentioned in the 974 Brut entry "bu varw Morgan" or "the death
of Morgan". If that identification is correct, then Morgan lived to an age near 90. That belief is said to be
the reason Morgan is called Hen or "the old", But since the typical Welsh nobleman of the era seldom lived past age
65, it might simply have designated him as the "older" Morgan to distinguish him from a same-named son. Perhaps there
was a Morgan ap Morgan Hen who died in 974, having been born about 915. And this younger Morgan may have fathered a
son, Idwallon, about 945.
In our companion
paper "King of England Mediates Welsh Dispute", we cite two events from the Text of the Book of Llan Dav, and show how its
c. 1150 author conflated them. And how, when separated, they compel the conclusion that Morgan Hen had a son named Morgan.
A third event from the same source suggests the same conclusion. 
we charted above should probably be emended following Morgan Mawr as :
885 Morgan Mawr/Hen
915 Morgan the younger