Look at thread leaf milkweed (Asclepias verticillate). The flowers are a bit of a different color, but they may just be older or there could some variation. ETA: Upon increased size, I think the flowers are different.

I know I've seen the plant before at a nursery, but what it was I don't recall.

Photos of that one:

https://www.bing.com/images/search?q=asclepias+verticillata&qpvt=asclepias+verticillata&FORM=IARRSM

Try seeking a name for your plant here:

https://www.facebook.com/groups/141908172522539/

I think it looks to brutish to be Asclepias verticillata or linaria. My first thought was Canary Islands too. Or maybe Socotra?

Asclepias verticillata.

Hymenolepis crithmifolia?

Photos of that one, which certainly looks similar:

https://www.bing.com/images/search?q=hymenolepis+crithmifolia&qpvt=hymenolepis+crithmifolia&FORM=IGRE

It looks like Hemenolepis, the plant, not the tapeworm. South Africa's close enough.

:) I'd already discounted my suggestion soon after posting with the ETA, before the follow-up comments. If I delete, sometimes the OP comment on it from their sent copy, and it causes confusion. If I retract, people ignore the retraction. ¯\_(ツ)_/¯

Looks a bit like Ozothamnus rosmarinifolius to me.

Look at the leaves, they are divided. Note also that to the right side of the picture we can see the flower heads are yellow, and not white from red buds.

Great job guys!

Hymenolepis crithmifolia looks like a very close bet! But the flowers are bright yellow on that... I wonder if the plant I saw just had faded flowers? Closer up pic below, and looking now I see all the flowers areopen, and white.

Phymaspermum acerosum (formerly Athanasia acerosa) is another idea...?

Both plants seem almost identical...

reading more: hymenolepsis crithmifolia synonyms: Athanasia, H. parviflora, H. crithmoides

So the yellow sections are still in bud, rather than being open heads. With the white ones being in bloom, rather than past. Showing once again that good close views such as this last one should always be included, when asking about any plants that may not be clearly and uniquely distinctive from farther back.

I grew H. crithmifolia for a while. The buds are greeny-yellow, flower open to bright yellow, dry to whiteish then brown up. It looks like an older plant as they get very woody after about 4 years. Looks like it was grown pretty dry. Mine got more water. I'd say yes, Hymenolepis crithmifolia, common name Coulter Bush, a South African wildflower. They were showing up in CA nurseries/garden centers 2-5 years ago. Native Sons was the wholesaler.

They were showing up in CA nurseries/garden centers 2-5 years ago. Native Sons was the wholesaler.

Native Sons offers some interesting plant stock, and I always run through the 4" sections at local nurseries where their uncommon offerings often appear. I knew I'd seen the OP plant at a nursery in recent years, although it might have been in one of their 1 gal. containers. Thanks for confirming it wasn't my imagination, hoovb.

Well it's just my imagination

Running away with me...

Interesting! I'll need to keep an eye out for Native Sons stock. Would love to have this plant - and I have grown and enjoyed Athanasia pinnata before. Annie's Annuals used to sell it.

Looks like San Marcos sells it: https://www.smgrowers.com/products/plants/plantdisplay.asp?plant_id=203