First off, here's a lovely specimen of Monarda citriodora, generally known around these parts as Purple Horsemint or Lemon Beebalm. When you gently crush the flowers in your hand, it emits a pungent aroma that some people think vaguely resembles lemon or oregano. Me? I think it smells like those stinky liniments like Ben-Gay or perhaps a combination of liniment and fennel. It's not unpleasant, but it's not something that I'd like to smell all the time. And these flowers emit this scent pretty freely when they're crushed.
The above picture and the one directly below depict Chamaecrista fasciculata, a legume commonly known as Partridge Pea. It's a legume, which means it is a distant cousin to peanuts, pinto beans, locust trees (which, interestingly, has leaves that look very much like the Partridge Pea), wisteria vines, and even the lupines like the Texas Bluebonnet.
Finally, I occasionally get asked about this one. It's Solanum elaeagnifolium, or Silver-leafed Nightshade. It is considered a noxious weed and is not only toxic to livestock, its stem is covered with nettle-like hairs that sting. In South Africa, this same species of plant is known colloquially as Satan's Bush. It can thrive under truly awful conditions, which is why it's so commonly seen on roadsides, and it's extremely difficult to eliminate because its roots will regrow even if there's just a half an inch of root left in the soil. It's not an unattractive plant, however, and gardeners who practice xeriscaping find this plant to be well-adapted to those conditions.