It's an annual, but don't tell that to this particular plant--or at least the particular patch of soil that it sprouts from. It pops up every year in this hardscrabble spot, and if the new blooms are really those of its scrappy seeds, so be it--it's still a dogged little thing.
I was surprised to learn that it's in the Brassicaceae family, kin to broccoli, cabbage, and the like. If the plants in my vegetable garden as well as the dwarf purple alyssum and the white "snow crystal" alyssum plants in my yard had an attention span, I'd lecture them about their brave cousin around the corner and how it blooms despite receiving no attention, scant water, and (when summer finally arrives) nothing but direct sunlight glaring off the pavement all day long. And how they really should be thriving given their optimal locations, well drained soil, and admiring gardeners. But you know plants. They pretend they don't hear you.
So I'll just continue to detour now and then while walking the dog to check on how this plant's doing. It's terribly obvious how this surprise bouquet functions as a symbol for so many themes (Resiliency; Nature's Restorative Powers: Adversity, Courage in Face of [see]; et cetera) so I won't belabor that point. I'll simply hope that the building's owners don't get the notion one day to zap the little metaphor with Round-Up like a crabby English professor reading the 127th essay of the day.