Lauren Brown lets the reader have it in her first sentence. “In New England, almost half the year is winter.” Yikes! I had never thought of it quite like that. “The flowers,” she goes on, “and the greenery that brought us so much pleasure from April to October are gone.” Put in those terms, she has a point. “Weeds and Wildflowers in Winter” is her call to take heart and join her in appreciating the more ascetic beauty still to be found in the hulls and stalks that summer’s glories have left behind.

Brown takes one by the hand like a sprightly aunt and leads us out into meadows, woods and marshes that at first sight look dead to the world. Her tone is determinedly casual, only resorting to botanical vocabulary when nothing else will do, and then with a punctilious definition that will satisfy the freshest of tyros. “You should know a little bit about how plants are classified.” She sounds almost apologetic, before diving into a quick brush-up on the differences between family, genus and species; and relieved when she concludes that “conventional botanical terminology is not very helpful for a lay person” facing a collection of dried, withered and broken floral remains.

What is helpful is the step-by-step key she has devised. It consists of pairs of contrasting alternatives ranked from 1 to 106. Starting at the beginning, whichever describes the specimen better points to a new couple of attributes to choose from, and so on, until the plant is correctly identified. Brown uses resolutely simple terms: “stands erect” vs. “lies prostrate” is the first. Should a scientific term creep in, a glossary is there to consult.

I love the logic behind keys with their promise that if you work diligently, your reward is assured. The reality, needless to say, is a lot less clear-cut. “Erect” or “prostrate” is easy, but beginners will find that choices get progressively less obvious as they near their goal.

Taking advantage of the recent thaw, I brought home a half-dozen baleful specimens and laid them out on the kitchen table. Using the key, I can confidently say I got four of them. The fifth could have been a couple of species. But I could not make head or tail of the sixth.

“You might prefer not to use the key and just to flip through the pages,” Brown offers, a bit reprovingly, although she allows that it is a “time-honored method… but your flipping will be more productive if you look for clues first.” I flipped and flipped, but to no avail. I have no idea what No. 6 was, but when I looked at the wispy forms through the magnifying glass, I found a miniature world of arcs and lines and dots that was as beautiful as a Japanese print.

That aspect of winter weeds is beautifully reflected in the line drawings that accompany each of the 135 different species of plant that Brown describes. These are the pages to which, with any luck, the key has directed you. Each one also has a useful paragraph or two describing the plant in more detail, always in Brown’s pleasant, conversational tone.

Here I learned, for instance, that goldenrod, contrary to popular belief, is not the cause of hay fever and for a reason that should be obvious. It is bright yellow in order to attract the insects it needs to pollenate it; its pollen is designed to stick to their bodies, not blow in the wind. The real culprit is ragweed, which flowers at the same time and whose pollen, light enough to be distributed by the wind, fills the air — and the nasal passages of the afflicted.

“Weeds and Wildflowers in Winter” was originally published in 1976 and is here reissued in an “updated package.” It is unclear to what extent if any the author has revised the text. Her comments on two particular species seem outdated, to say the least. Purple Loosestrife, she tells us, has been “quite successful in establishing itself,” which seems to understate both the success and the dire ecological impact of this aggressive invasive plant.

American Bittersweet, Brown cautions, may be disappearing because of over-harvesting for its decorative berries. More likely it has been driven out by competition from and hybridization with its oriental cousin, another frightful invasive that also attracts the uninitiated with its colorful fruit. The publisher would have done a great service by pointing out the difference, or even redacting Brown’s cheerful advice to “try not to take too much” and to “try planting it in your garden.”

Nonetheless, it is hard not to agree with the great Roger Tory Peterson’s comment when this elegant book first came out. “For many years, I have wished for a book like this.” Here it is again, so take it with you the next time you venture out into the cold.

Thomas Urquhart is a former director of Maine Audubon and author of “For the Beauty of the Earth.”