What the heck is a pencil plant? Is it a plant whose stems are used to make pencils? A flower which somehow resembles a pencil point? Something else entirely?

Nope, the pencil plant, (Latin name is verbena bonariensis) is a tall, thin, self-sowing annual whose slender form rises on a sturdy square stem that, to some eyes, must look like a pencil.

Considered an heirloom flower, it was a favorite in the Victorian cottage garden. Its blossom is an airy cluster of violet-blue at the top of the 4- to 5-foot plant, and is extraordinarily attractive to the monarchs, swallowtails and other butterflies who visit during the warm days of midsummer to frost.

This verbena is also lovely in the vase, where her shape, complexion and height complement other gleanings such as roses, hydrangea and obedient plant. I've been told she even has a slight fragrance. But alas, my insensitive nose can't detect it!

Though verbena bonariensis commences full bloom in late July, she's obtainable primarily in the spring. So make a note in your garden diary (you DO have a garden diary, don't you?) to purchase a six-pack of this willowy lady from local nurseries such as Dom's Garden Center in Danbury next May. Or order her from the spring catalogues of Bluestone Perennials (www.bluestoneperennials.com or Burpee www.burpee.com).

Native to tropical South America, and named after Buenos Aires, this verbena, like most, appreciates full sun and moist, organic soil, though she's drought-tolerant and will grow and bloom in less than optimal conditions.

One of her monikers, "verbena on a stick," illustrates her propensity to weave (but not flop!) in and out of a perennial bed or border. Because she's so thin, and her flowers are borne up top, her footprint isn't large, and she can be placed at the front of the border. She's a "see-through" plant, and can be just as readily admired at the middle or back of the bed, too.

Lost to memory is how I acquired my first verbena bonariensis. Did I start her from seed, purchase a cell pack or was she a pass along plant? All I know is she's happily lived in my yard for many years and, as long as there's a modicum of sun, she jumps willy-nilly into my various gardens.

I've learned to recognize her seedlings, the elongated oval shape of her seedling leaves, and each June I welcome her back. I coddle her where I want her, but if she's too enthusiastic I either transplant to a more desired locale, or plunk her onto the compost pile.

In some areas, such as the Caribbean, verbena bonariensis is considered an invasive, and she's naturalized in a number of southern states, but our cold climes keep her in check.

This pretty purple verbena remains one of the delights of the northern late-season garden. A lovely pencil plant indeed, not only for you, the tiller of the soil, but for those winged wonders who depend upon your garden, the butterflies.

Colleen Plimpton will be teaching gardening in small, hands-on classes this October. Contact her at colleenplimpton@yahoo.com for further information. Follow her gardening blog at www.colleenplimpton.blogspot.com