This is a widely planted tropical American shrub that is just covered with brilliant pink flower heads during warm weather. They are extremely fragrant at night. It smells to me a lot like Hoya carnosa and fills the growing area. It is in family Rubiaceae, with other very fragrant-flowered plants coffee and Gardenia. Its specific name refers to the white undersides of the leaves.
The Chicago Botanical Garden has more photos and some information.
I've tried to grow this on and off for over 30 years. The only plants I could find were tiny little cuttings from Logee's that never survived. Finally I found a source for a plant big enough to survive. This came last July in a 3.5"/9cm pot from Almost Eden nursery. I immediately moved it to a 1 gallon pot, and it took off growing. It has more than quadrupled in size. I'ts been in flower almost since it arrived. I initially planned on moving it to a 5 gallon / 21 liter pot, but since it flowers so much in this smaller pot, it's staying there.
I must warn you that 7 months after it arrived, I found Florida wax scale on this plant. I don't know whether it came from this nursery. I have sprayed it with neem oil and the scale seem to be gone.