Something in the Heliantheae tribe of Asteraceae? Melanthera? I don't like the leaf margins for Melanthera biflora, though maybe that's variable. I'm certainly seeing very different leaves with that name.
Many thanks wcutler. Melanthera seems to fit in many ways..black anthers, square stems, mottled stem, ...fruits Quote wiki.... "The most common species of this genus is Melanthera biflora, found in the coastal areas and islands of the tropical belt of the Indo-Pacific region., Melanthera biflora is usually one of the first species colonizing degraded or altered environments in tropical zones of the planet." It was found on the side of a dirt track! Just struggling with the leaf shape for 100% match.
The foreground leaves in the third photo match what is on the page you cited. It's interesting in that photo that the margins of the leaves in the background are what I thought were different enough to give me pause, but they are on the same plant. There are several synonyms, the most popular of which seems to be Wollastonia biflora.
