These seeds are from Acacia salicina, a tree native to Australia but also grown in the southwestern United States. It has various common names, one of which is "willow acacia," because of its draping, willow-like appearance.
The powderpuff blossoms attract bees and butterflies.
After pollination, the flowers produce these:
Any guesses what the bright red or orange fleshy structures next to the seeds are? Those are very interesting. They are called "elaiosomes," meaning literally "oily bodies." The tail-like parts are like a brightly-colored potato chip stuck to the seed. The birds eat the potato chip part and often carry off the seed with it. They drop the seed unharmed when they are done. The seed is thus moved away from its parent or dispersed. Botanically the structure is called an "aril," which has to do with what part of the plant the elaiosome is derived from.
I started you with a tricky one, because it is only found in the desert. Common names for these plants are barrel cactus and fishhook cactus. The scientific name is Ferocactus.
The name fishhook cactus comes from the fish hook shape of the spines of certain species. I have read that the American Indians of some tribes did use them for fish hooks.
It is also called the compass cactus because in natural settings the shady side grows longer and the cactus tilts to the South.
The flowers are sources of nectar and pollen for bees.
The bright yellow fruit are supposedly eaten by deer and certain rodents.
For more about the special relationship between ants and barrel cacti, see my Wild About Ants blog.
This week's mystery seed:
The shiny, hard black seeds of the barrel cactus reminded me of the seeds of another plant in our yard. This time I'll give you a hint. The mystery seeds this week might be easier for our Australian friends to identify.