Hymenocallis littoralis (I think)
I forgot how beautiful these are. I had a Hymenocallis littoralis by the gate where it was at first fat and happy, but then it grew so much more fat and happy I couldn't get through the gate anymore and was fearful it would be a Bermuda Triangle of sorts for small pets and children.
I exiled the beast to a grim dry spot under the Brugmansia, where it has finally recovered--and triumphed--after three years of struggling against drought.
I'm not completely sure of the species. I've searched via The Google, and see multiple identifications. Part of the complexity in identification is bloom time--apparently there are very similar species differentiated by their general bloom time.
The only place I've seen another Hymenocallis is the Huntington, and it was a different species. I've never seen it for sale in a local garden center.
I got mine from a neighbor; her landscape architect selected and planted it back around 1972. It's been an increasing clump ever since, and my neighbor gave me an offset. I'm surprised it isn't popular, because it's easy; the only serious problem is snails. Mine grows with help from me beyond proper placement (part shade) and water.
The foliage is strap-like and resembles Agapanthus foliage in size and color, but with less substance. Snails love the foliage for both housing and meals, so a grim dry location was somewhat a favor as well as a punishment: I've seen no snail damage at all. I really did forget how beautiful they are--my specimen chose to survive and remind me.
Hymenocallis means "beautiful membrane". A common name is "Spider Lily"; it should be noted that other genus are also known by that common name. The genus is a member of the Amaryllidaceae family. Some more information here explains perhaps why I'm not sure of the species, because many species seem to have
very similar flowers--at least they look similar in tiny little pictures.