Portulaca. If you’re looking for a plant that can withstand the heat of a DC summer in a roof garden, this is the one. Plus, you can eat it! (Though you probably don’t want to. It’s pretty sour.)
cheekecheeke
+1 they are so cool!
Brentwood
Love portulacas. I used to have a whole field of them in my yard, until I forgot/was too lazy to weed. I also find trailing verbenas do well in my ground-level garden (plus I get to spend 5 minutes standing in front of my gate every morning deadheading them, which I find very satisfying).
Mostly Cloudy 
