Don Gardner and Gerry Carr of the University of Hawai`i identified it as Dubautia arborea, an endemic tar weed related to the silverswords, found only on the Big Island.
Closeup of the top of the tallest branch, carrying what appear
to be seed pods. There were also the remains of much more delicate
flowers (male?) elsewhere on the plant (single, on the ends of stalks
a few inches long which branched in threes from a central stalk).
A fairly common shrub around Hale Pohaku, with sliver-green spade-shaped
leaves. According to Don Gardner and Gerry Carr, it is probably
Chenopodium oahuense, another endemic found on all the
islands.
A closeup of a vine that was overrunning many mamane trees in the region
west of Hale Pohaku. Is this native, or yet another alien weed?