Hi Carol, I believe most of the trees with Arderns have probably taken the informaton from this book:
https://archive.org/details/shakespearesfami00stopuoft
According to the author, the Henry you mentioned was the son of Siward and Cecily.
https://archive.org/stream/shakespearesfami00stopuoft#page/165/mode/1up/search/siward
I have no idea how accurate the line is, which is always important to consider. This is not currently on Wikitree.