I obtained seeds from
Datura plants of the same type that I saw in front of the school in September. Those plants were cut down a couple of days later*, and so there went any thought of collecting seeds. Or so it seemed.
Last week, as some of the teachers and I returned from a chrysanthemum festival hosted by the neighboring agricultural high school, I spotted the withered remains of some
Datura inoxia (I think) along a hedgerow. When I went to check them out yesterday, I found that several of the stems had been snapped or trampled upon. I found two or three viable pods and brought them home to dry alongside the seeds from
the double-flowered D. stramonium.

Datura inoxia and its seed pods
Datura stramonium var. tatula and its seeds
(and a citrine shard)*My co-teacher asked the building and grounds maintenance men to take me to where I saw the seed pods last week. From what I could gather from body language and facial expressions, it seems that
Datura is considered a bit of a weed [the name for
Datura in Korean, 흰독말풀, can be translated as "white-flower pondweed"]. The men repeatedly made this chopping motion with their arms and wanted to move on.
As I walked back to the school, I saw remnants of the chopped stems from September... including a few that had re-sprouted. I dug up a couple and will pot them on Friday.
Some earlier Datura discourse