The word "caper" can be used in a couple of very different ways. As a verb, it means to hop or jump around playfully, perhaps dancing; Shakespeare uses the word this way a number of times in his plays. As a noun, it usually means a sort of shady or criminal operation…something like a heist (as in when Howard robbed the bank in Mayberry).
Its other usage as a noun often involves  mysterious soft, little green things, with a curiously peppery flavor, packed in brine or vinegar, that usually come out of a narrow jar, sometimes ending up on top of a marvelous smoked salmon at a holiday party or special dinner.
There are actually a fair number of species in its genus, but the commonly-known caper plant is of Asian origin, and it is now widely grown from Israel to Spain-- and also California. It is a shrubby sort of plant, with bright green oval leaves (and stickers), tending to trail, and often becoming viny. This is a plant that really likes it hot and dry, and with plenty of sun. The wild forms of it are quite at home in desperate places, often growing out of cracks between rocks or bricks. Such plants are sometimes seen forming trailing shrubbery on old walls and ruins in the Mediterranean.
Commercially available capers are the buds of this plant, and they come in a variety of sizes, depending mostly on their age. The youngest (and smallest) buds are the hardest and most labor-intensive to pick, so they are the most expensive…but of course, it also takes more of the tiny ones to fill up a jar. The size doesn't seem to make much difference with the taste, though. If a bud is left alone, unpicked, it will eventually open up, and a beautiful flower results. Each flower has four asymmetric green sepals, four larger, white petals, and lot of slender, delicate stamens. Gardeners would recognize this flower as a bit similar to the old-fashioned spider-flower, and indeed, the caper plant is botanically related to it.  It's also related to plants of the mustard family, having similar flower structure, and sharing some of the various compounds which give these plants their sharp, mustardy flavor. Within the caper flower is a small ovary on an elongated, slender stalk (the ovary is thus "stipitate"). After pollination, the ovary, containing tiny seeds, will swell, eventually becoming large enough itself for harvesting: this would be a "caper-berry." The convenient little "handle" of a caper berry (martini, anyone?) is the grown-up ovary stalk, from the flower. The stalk won't be seen on a caper, so there's a big difference between the two. Capers (and caper berries) are often seen for sale fresh, in bulk, in local markets. They are more likely to be stored in oil, or pickled in brine or vinegar, or even packed in salt. Nothing quite matches their lemony, peppery tang.

 [Answer: "Capers," Capparis spinosa]

John Nelson is the curator of the Herbarium at the University of South Carolina. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call 803-777-8196.