Consistent Background Details On Avalon

"Wingless."

Nat Falkayn addresses his Ythrian friends, who do not seem to have learned Anglic, in Planha:

"'I've been sailing myself, around First Island...'" (p. 417)

Liaw of the Tarns, Wyvan of the High Khruath of Avalon:

"...and his colleagues stood on the olden site, First Island in the Hesperian Sea. At their backs rose the house of David Falkayn; before them greensward slanted toward beach and surf."

-Poul Anderson, The People Of The Wind IN Anderson, Rise Of The Terran Empire (Riverdale, NY, 2011), pp. 437-662 AT XI, p. 561.

So we infer that Chartertown (see Nicholas Falkayn, Engineer) is on First Island. (Three generation of Falkayns.)

"Whirlpools seethed. In them, thick brown nets of atlantis weed, torn loose from a greater mass far out to sea, snaked around and around." ("Wingless," ibid.)

"'We'd take three or four days to reach the nearest atlantis weed as Olga dubbed it."

-Poul Anderson, "The Problem of Pain" IN Anderson, The Earth Book Of Stormgate (New York, 1979), pp. 26-48 AT p. 34.

So Olga Berg named the atlantis weed. In this story, surgeon trees and hell shrubs are also named. "...monstrous marine creatures..." (p. 33) are mentioned without being named yet. Don't you want to go there?