PlantFiles: Wild Poinsettia, Japanese Poinsettia, Summer Poinsettia, Hypocrite Poinsettia
Euphorbia heterophylla

The fruit is a capsule.

This plant has been in my yard for years. It was more common before I began cultivating my yard. It still shows up now and then between cultivated plants and bushes, but I would not consider it seriously invasive.
I always considered it a weed until recently when our small garden club (S Fla Galloping Gardeners) toured a local nursery. One of the members commented on this plant growing wild off to the side of the display tables. I mentioned I had them growing wild in my yard too. I gave her a plant I dug up for her and we have been talking about it ever since.
We recently discovered it's name and I posted a picture of it here.
The plant is a good source of nectar for attracting butterflies, especially in the "off" season when there is not much else blooming in zone 10.
The milk from the plant can cause irritations to the skin so handle it carefully. All parts of the plant are poisonous if ingested.
I usually find new shoots of this plant in the area under the overhead utility lines that border the E side of my property. To me, this indicates birds eat the seeds.
The plant is native to Florida.