ipomoea species seed harvesting times question

[jokergrin]

Ok, so I've been growing Heavenly Blue Ipomoeas all year and have been able to harvest seed all year.

I just recently found an enormous vine growing near my apartment.  These are NOT heavenly blues, but are Ipomoea purpurea (I'm guessing) and are DEEP purple in color.  They still have the heart-shaped leaves and are characteristic morning glories.

My question is, the latter vine that I happened upon have NO ripe seeds....but the seeds all seem to be riepning at the same time...so in a week or two there will be a LARGE amount of seed all at once.

So, is this variation in seed production times just a differentiation in species?  Has anyone else noticed this?

Thanks for any info.

-jg