I'm wondering if this is a Ludwigia. The buds look right. I don't know any of them personally. I hope Jay sees this post.

ETA now I'm wondering about Calylophus. I've never seen any of them either.

Yes...I think we are on the right track here, but the evolving naming conventions are confusing... Like, are these all different names for the same plant?

Calylophus berlandieri (Sundrops)

Calylophus berlandieri ssp. pinifolius (Texas Primrose)

Calylophus drummondianus (Texas Primrose)

Calylophus drummondianus (Texas Sundrop)

Many plants have several common names. That's why the scentific names are imortant. Calylophus has been reduced from a genus into a section of Oenothera. Calylophus berlandieri subsp. pinifolius has been elevated to species status and is now named Oenothers capillifolia. A type species can be secure in the wild, but it might jave a subspecies in danger of extinction. Giving varieties and subspecies species status helps protect them. I love seeing the histories about how the names evolved.

Oenothera capillifolia formerly Calylophus berlandieri subsp. pinifolius. Easy to spot with it's black throat.

It is confusing that so many members of the EVENING PRIMOSE FAMILY are called SUNDROPS. Looks almost identical to Oenothera berlandieri in every other way.

^ Oh wow, thanks! So, you're saying that if these have black throats, then they're Oenothera capillifolia. But if not, then they're Oenothera berlandieri?

Yes, correct. I wonder if I can grow it here? I love lemon colored flowers with dark throats like Abelmoschus manihot and Hibiscus trionum.