In the airy bathroom of a Clerkenwell town house, the dark, oak-leafed foliage of a Cissus rhombifolia Ellen Danica peeks over the edge of a heavy marble tub.

Next to the pens and Post-it notes neatly arranged on the desk is a pot in which grows a Cissus rhombifolia plant, a grape ivy, and beside it are cuttings of green plants. Plants can soothe, help ...