One difficulty is that a species that is weedy in one place may be perfectly well behaved in another. Andrew Wilson mentioned O. convexula, which gives us a good example of this phenomenon: evidently well behaved at Mary Sue's in northern California, apparently a thug of the first water in San Diego. If our wiki is to include information on weediness, it would be even more helpful if instances of weediness were accompanied with specifics of location; the name of the city would usually be enough. Indeed, location is all-important in determining whether a plant will thrive or not. Plants which are dead easy in, say, the eastern US not uncommonly turn out to be invalids in the PacNW, and vice versa. The annual variation in temperature and precipitation are perhaps the primary factors, but by no means the only one. Soil pH (or perhaps the concentration of free Ca++ ions in the soil) is another important factor. All the more reason, everyone, to remember to include your location in your .sig block -- Rodger Whitlock Victoria, British Columbia, Canada