Both species are established feral plants here in the greater Washington, D.C. area. Of the two, O. umbellatum is the more commonly encountered. This species does not seem to set viable seed - at any rate, I've never known it to do so. But every scrap of living bulb seems endowed with an inalienable right to near immortality. Ornithogalum nutans, although less frequently encountered, sets viable seed. A feral clump I have observed off and on for decades has not spread much at all. It has also been my experience that bulbs of this species do not respond well to drying. Jim McKenney jimmckenney@jimmckenney.com Montgomery County, Maryland, USA, USDA zone 7 My Virtual Maryland Garden http://www.jimmckenney.com/ Webmaster Potomac Valley Chapter, NARGS Editor PVC Bulletin http://www.pvcnargs.org/ Webmaster Potomac Lily Society http://www.potomaclilysociety.org/