These could be from the family of Composites include many great garden plants and – yes – many weeds with a great talent for spreading their seeds around, as your plant might do in exactly the way that dandelions do (yup, same family). They can be notoriously hard to identify even when the flower is present. However, we believe your weed is in this plant family and while it resembles the Willow Aster, we found a similar weed, the Oldfield Aster, that it may more closely resemble. You can do a google or yahoo image search to see if you weed more closely resembles this aster. Regardless of it’s official name, the removal strategy is the same. Hand pulling when the soil is moist, not letting the blossoms go to seed, and considering using a broadleaf herbicide. You may want to check with a local nursery for the best herbicide options and instructions. You have a lovely garden bed – best of luck to you in managing your weedy intruder!