2. The visual impression of poporo at first is some kind of young plant growing with a straight slender stem from a seed and ending with a stylized leafy top:

The stylized top suggests that also the slender straight stem and the seed may be stylized and without any ambition to present a natural picture.

If so, then the glyph type may very well be a composition of three parts: seed, stem, and top. There are very few glyphs of this type, which fact supports the idea of a complex of signs.

The top is like the wedge sign inside henua ora, though upside down:

And then, we realize, also the stem will be explained.

An upside down 'recycling station' (henua ora) must - if the rongorongo system of writing is consistent - mean its opposite, viz. the station which produces new things. The seed at bottom confirms the idea.