Montana's more than two thousand species of flowers and many nonflowering plants may be divided into three somewhat overlapping groups --subalpine, montane, and plains.
The subalpine group, characterized by plants that appeared after the recession of the glaciers, or moved in along the mountains from the Arctic, has made the higher altitudes in the northern Rockies famous for their profusion of color in the short midsummer season. When the snowbanks melt and all the flowers bloom at once, the earth is brilliant with glacier lilies, alpine poppies, columbines, white dryads, globeflowers, Indian paint-brushes, asters, and arnicas. The summits are, on the whole, too rigorous for any marked growth of shrubbery, but white and purple heathers, Rocky Mountain laurel, and Labrador teas are present.
The montane group includes most of the coniferous forests, and ranges from the lower border of the subalpine to the valley grasslands. Its most characteristic species is the spire-crowned alpine fir, sometimes associated with Engelmann spruce and white-barked and limber pine (also known as limber-twig pine). There are many shrubs: huckleberries, Menziesia, mountain ash, and scrubby birches and alders. Blue phacelia and, in damp places, red monkey flower and fringed parnassia are conspicuous. In the moister parts of the lower montane forest are Moneses and prince's pine, lowland and Douglas fir, and western larch; but in dry places, lodgepole and western yellow pine, and mountain balsam are more common. Bear grass lifts its beautiful domed column of white blossoms among Mariposa lilies, dogtooth violets, and windflowers. There are many shrubs, such as kinnikinnick, which are not found in the upper montane.
The plains group varies, being characterized on the eastern prairie by grasses such as buffalo and blue grama; in the west, by bunch grasses and by flowers such as the yellow bell, shooting star, bluebell, blanketflower or gaillardia, golden aster, and daisy. On the eastern grasslands are found sand and gumbo lilies, prairie evening primrose, and a little shrubby scarlet mallow with conspicuous waxy petals; clumps of small cacti bear red and yellow blossoms of a delicacy hard to reconcile with the aspect of the plants themselves. Wherever overgrazing, fire, or erosion has destroyed the soil's water-holding capacity, desert shrubs from the south have crept in; the familiar sagebrush is found with greasewood, sea blite, ranger brush, and mountain mahogany. Moist areas are often called camas prairies because of the blue camas, an onionlike May-blooming plant used by the Indians in making pemmican. Death camas, a plant similar to blue camas, but highly toxic, has caused heavy losses among sheep; even men, mistaking it for blue camas, have been poisoned. It bears a star-shaped flower, usually white; its grasslike leaves are most often folded. Common on the plains are yucca or Spanish bayonet, many species of Pentstemon, and sego lily, which blossoms in nearly every color.
Subsurface moisture encourages stream bank forests composed largely of cottonwood and aspen, but often containing alders, river birches, willow, and the like. In swampy areas, cattail, bulrush, and water plantain flourish beside water buttercups and various mints. Coulees and other favored grassland spots support serviceberry, currant, gooseberry, hawthorn, fragrant mock orange, and wild rose.
The State flower is the bitterroot. Flathead Indians who used its root for food gave it the name later applied to the valley, river, and mountains of the region where it was found most abundantly. It is small, with a rosette of 12 to 18 leaves; its low-set pink blossoms turn white after a few days in the sun. White men called it Lewisia in honor of Captain Meriwether Lewis, and rediviva (Lat., lives again) in recognition of its vitality. The gumbo lily, most abundant in Carbon County, is like the bitterroot, and even more beautiful. It is not so commonly found, however.
Montana's four species of cactus are much smaller than southwestern ones. Most common is prickly pear, valued in the East as a houseplant because of the indescribably tender tints of its blossoms. In Montana its beds of sharp spines would make it a pest--if anything so beautiful could be a pest. Cacti are very easily transplanted; a stem set in the ground will take root.
Wild roses are common along mountain trails as well as in coulees on the plains. A low-growing variety sometimes becomes a nuisance in fields.
Sagebrush, common on open plain and hillside, is an erect shrub, one to six feet high, with many branches, silver-gray leaves, and small, clustered yellow flowers.
The Oregon grape of the lower montane forests has bright yellow flowers and glossy green leaves. The stem is thick, the root a yellowish hardwood used by Indians in concocting stomach medicine and spring tonics. In autumn the fruit, a small, blue, rather bitter grape, is used in making jelly. The plant grows in shaded places, often near large rocks. It is conspicuous in autumn, when, after other growth is gone, a single leaf may present an array of orange, brown, and red.
Kinnikinnick, with its small red berries, also provides much autumn color. It grows in great vinelike masses over large rocks; its sturdy root often spreads several feet; its small dark green leaves provide food for deer and other animals. The Indians used its bark for smoking.
Mountain mahogany grows in the hills, and the pussy willow thrives along the banks of streams in all parts of Montana. Foothills and valley are well stocked with edible berries: huckleberries, currants, gooseberries, chokecherries, serviceberries, and buffalo or bull berries. A few wild cherries grow near Martinsdale, in Meagher County. Wild strawberries and raspberries are found in many wooded sections.
Montana has many varieties of forage grass. Some of the most important are June, wheat, and pine grasses, bluejoint, and bluestem. Besides the grasses, edible ferns and mosses flourish in the forests. When forage grasses are overgrazed, an almost worthless "cheat grass" sometimes takes their place. Nourishing enough early in the spring, it is spoiled by summer weather.
Foxtail is a detriment to some pastures. At the top of an 8-inch stem it bears a spiculate tassel resembling the tail of a fox. Animals seldom attempt to eat it, but if they do the bristles may stick in their throats. Feather grass and needle grass, both species of Stipa, are other nuisance grasses. When ripe, their twisted awns catch in the wool of sheep, work into the skin and eyes, and cause infections and blindness.
Among Montana's worst weeds are Russian thistle and "Jim Hill" mustard, both tumbleweeds. Easily uprooted or broken off at the base, they roll before the wind, scattering seeds, and then pile up along fences. High winds strike these walls of piled weeds with such force that miles of fence are sometimes torn up and dragged out into the fields.