Yup, Osteospermum (AKA African Daisy & Sunscape Daisy).
I just love these plants! Here's one of mine,
& here are some of Bills.
(Your photo is awesome, Gailo!)
I'm so glad that you didn't
weed it out when it came up among your Petunias... you're going to love it! I especially like mine because they're long-lasting in cut
flower arangements, & the
plants are hardy. (I've neglected to water them at times, but they seem to be somewhat draught tolerant & perked back up quickly!) I've never harvested
seeds from mine, as I use them a lot in small arrangements before they get the chance to go to
seed. (I found that they'll take hold fast & send roots down just by breaking off a stem & sticking it in the ground...
so who needs seeds, anyway? This is faster!) As Bill's link mentions, they do best in full sun. Most of mine are, but I have some that only get afternoon sun & they seem to be happy, too. I read somewhere that while the
plant will thrive, it might not make
flowers without direct sunlight.
This past winter was colder than normal, & we had freezing temps (upper 20's), where we usually don't get below the mid 30's. I hadn't winterized anything in my gardens, & was afraid that I'd lost my African Daisies. Then, this is what I found in late April...
growing from the ends of a big mess of dead-looking stems!
I went through it all & clipped off the dried up dead stuff, then covered the leggy surviving stems with the loose soil in the garden bed, & they took right off... & even sent up new
plants!
(I sent one of the survivors to Illinois in early May, & it didn't seem to mind being closed up in in a baggie for 4 days!)
Even though I know now that they'll tolerate the abuses of winter, I plan to mulch them over this year. I think they'll be happier, & so will I!