I purchased these tubers originally from Van Bourgondien's from their wholesale catalog back in 1978.  They were listed as tropical plants requiring zone 10.  I live in zone 7a but am not always very conscientious about bringing plants in to safety in October.  I was surprised the following spring to see them come back stronger with a few seedlings. 

When I moved to my current home in Setauket, I brought a couple of them with me.  They've continued to come back every year since.  They seed themselves and have multiplied into groups of 10 and 20 and more.  I've given several away and yet have them coming back each year.   Some have apparently been spread by local critters and are coming up in remote corners of the yard. (...and no, they're not becoming weeds)

After a long time, they've created a dense attractive bed, reliably returning every year once the weather warms up:	Before the foliage, the larger tubers bloom.  You can see flies exploring this bloom.  The bloom smells like something that would attract those flies.  Fortunately, that smell lasts one day and one day only.	After bloom, a seed pod develops. I have not noticed any resulting seedlings before the following spring.	This larger collection was mislabled as Sauromatum giganteum when I purchased it on eBay.  It's clearly not S. giganteum but rather just a giant form of S. venosum.  The largest leaves are twice the size of those in the regular venosum bed.