Are the stems a bit fuzzy? It looks like one of the Gnaphalium spp. A frequent common name is cudweed. Don't let the first few pics online dissuade you with their velvety leaves. There are many species, and variability. This could have come in with your mulch, or with your celosia (yellow plumed flower in background), or just be a common weed in your area. The roots will be insubstantial, and eventual flowering is not showy. Pull it fast and compost only if there are no signs of flowering.
