Ideas:

1. I believe that we can here see a nut of some sort, from which a sprout is arising. The nut is like a head. Quite in accordance with the Polynesian image system. Heads are nuts.

2. If we compare with the parallel glyph in Small Santiago

we can see that here the sprout is crowned by something looking like a half-moon. Possibly this is to indicate the rim of light resulting from the fire-making at the heart of the sky (which ought to be located at the South Pole seen from south of the equator).