Day 275: What defines a weed? Most people think of weeds in terms of a plant which takes over gardens and lawns, out-competing the things we want to have in their place. By this definition, both White Lawn Clover (Trifolium repens, non-native) and Pineapple weed (Matricaria discoidea, native to the PNW) are "weeds," despite the fact that what they may be displacing are cultivars not otherwise known in North America. To a naturalist, a weed is any introduced species, a definition which excludes Pineapple weed despite its tendency to take over disturbed areas, and one which could be extended to include your prize marigolds. Location is often a factor in defining "weed" species, e.g., horsetails (Equisetum arvense) are native in the PNW, considered an invasive of the first order in other areas of the US.
This brings us to the debatable status of Silene vulgaris, Bladder Campion. It is an introduced species, but it is not invasive. In fact, it is generally rather short-lived when it does appear and does not out-compete natives. It occurs most frequently on disturbed soils (roadsides, trail margins), but seldom extends into the thicker growth of meadows. Unlike our native Campions, Silene vulgaris is the only one which bears male and female organs in the same flower. You'd think that would give it an advantage, but apparently it does not. However, like our native Silenes, it has a strong point working in its favour: it's pretty (of course, that's the same logic which brought us dandelions), but since it poses no significant threat, I'm not too inclined to yank it out when I find it.
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