Re: can you ID this Cyathea?
The most remarkable property of the "hybrid" is the extremely fast maturation. The "spore-to-spore" time was just 25month! Two other spore samples, I presume C.coopery and C.browni, were seeded simultaneously. C.coopery become fertile a year after the "hybrid", whereas C.browni 7 years on still has no spores. The "hybrid" spores are viable and fast to produce protallys. I would expect some fertility issues from a hybid. C.marcescens is well known example.
Still Eduard's hypothesis has a good chance as I had C.coopery and C.browni specimens sids-by-side when early protallys were replanted in one "sporelining" box. Here: three bottom rows are Cyathea leichardtiana, Cyathea brownii and Cyathea cooperi.
On the other hand the plants are "C.cooperi", "C.browni" or "C.mistery" only in my opinion. I hope you will agree with me on the first two at least.
Early days when I collected spores in RBG Melbourne I labelled them "cooperi" or "browni" almost randomly. As result I used spores from these three plants (below) and later randomly peaked few sporelins from every germline. So they all are of nameless descent.