The words ‘companion’ and ‘accent’ are used interchangeably to indicate a plant or object used in bonsai display. Last year I made a post of several in my backyard… http://crataegus.com/2010/05/13/accents/
…and here are a few more.
I have been heavily focused on Northwest native perennials since moving to Portland, Oregon. Part of the reason is that many of the nursery offerings seem a bit gaudy to me, not quite the austere, honest look we try to find in all our bonsai and in their accessories. (I made one exception here with a purple columbine, a genus which I have a weakness for… my purple one is a double-flowered variety, and doubtless the result of some savvy breeding.)
Some months of the year I’m as easily excited about accents as the bonsai. One of the curiosities of accents is that depending on how the perennial grows that year, or is trimmed, or simply flowers that week, the front of it changes.