Bohemian knotweed (Fallopia × bohemica) is a fertile hybrid between two highly invasive plants, Japanese knotweed and giant knotweed, and it shares features of both of those plants. The hybrid was introduced into North American and cultivated as an ornamental. It escaped from cultivation and is now naturalized across northern United States. It is reported to be partially or fully fertile, but it spreads mostly by rhizomes and by the dispersal of plant fragments.
Bohemian knotweed is found on river banks, along roadways, and in other disturbed areas. It often forms large dense colonies. Its bamboo-like stems are erect, stiff, and hollow, and usually have many long slender branches. The leaves are up to 12″ long and may be spade-shaped, straight across at the base, or slightly heart-shaped, indented at the base. Both leaf shapes may appear on the same branch. Flowers appear from July to October. The inflorescence may be long, narrow, and unbranched, or short, broad, branched, and plume-like, and it may be either shorter or longer than the nearest leaf.
Though one parent, Japanese knotweed, is listed as invasive in Minnesota, this hybrid is not … yet.
Bluntleaf sandwort (Moehringia lateriflora) is a common but often overlooked perennial forb. It occurs in Asia, northern Europe, and North America. In the United States it is common in the northern tier of states but absent in the south. It is very common in Minnesota. It is found in woodland edges and openings, open woodlands, and gravely riverbanks, and less commonly in meadows and prairies.
Bluntleaf sandwort is a low plant. The stems are much branched, less than 12″ long, and weak. They either curve up from the base or recline on the ground with only the tip ascending. The leaves are opposite, broadly ellipse-shaped, and no more than 1¼″ long. From mid-spring to early summer it produces a few small but showy white flowers.
Bluntleaf sandwort is similar in appearance to chickweeds, but the petals are neither deeply cut nor notched.
Bryophytes are small, seedless, nonvascular plants. Because they lack vascular tissue, they also lack true stems, leaves, flowers, and roots. They grow low to the ground and absorb water by osmosis. The three major groups of bryophytes are mosses, liverworts, and hornworts. Liverworts have prominent gametophytes, which is the sexual phase in the life cycle of plants. Thalloid liverworts consist of a flattened mass of tissue (thallus).
Water liverwort (Marchantia aquatica) is one of the largest thalloid liverworts. It is found across North America and in Europe. It grows on moist or wet soil in swamps, calcareous fens, wet meadows, cliffs, springs, disturbed areas, and recently burned areas. It often forms colonies of overlapping plants, sometimes creating extensive mats. It can be a pest if allowed to invade a greenhouse.
Liverworts reproduce both sexually and asexually. The asexual reproductive structure of water liverwort is a splash cup (gemma cup) that is produced on the upper surface of the thallus. The cups are green, circular, and shallow, and contain a few gemmae. The gemmae are dispersed when they are splashed out by raindrops. Each gemma can produce one or two plants if it lands on soil.
Water liverwort is distinguished from its close look-alikes by a dark, midrib-like furrow on the thallus that is uninterrupted and conspicuous.
Wintergreen (Gaultheria procumbens) is a slow-growing, perennial, evergreen, 2″ to 8″ tall, dwarf shrub. It is common in most of its range from Maine to Minnesota and south along the Appalachian Mountains to Georgia. It is fairly common in northeast and northcentral Minnesota. It grows in dry or moist woodlands, in partial sun or light shade, in nutrient poor, acidic soil.
The upright stems of wintergreen are actually branches rising from a horizontal stem lying flat on the ground or buried just under the surface. Two to five shiny green leaves are crowded at the top of the stem, and one to three white flowers droop from the upper leaf axils. The flowers are replaced in September by bright red berry-like capsules. The leaves and berries are edible and have a minty, wintergreen fragrance and flavor.
Wintergreen contains the aromatic compound methyl salicylate. In the past, oil of wintergreen has been used as a natural flavor in chewing gum, candy, soft drinks, toothpaste, and snuff. Dried leaves have been used to make tea, giving it another common name “teaberry”. In large amounts oil of wintergreen is toxic. Today, methyl salicylate is produced artificially for commercial uses.
Poison sumac (Toxicodendron vernix) is unfamiliar to most hikers because it grows in swamps, marshes, and wet meadows, places that most hikers avoid. In Minnesota, it is found only in nine east-central counties.
Poison sumac looks similar to distant relatives smooth sumac and staghorn sumac, neither of which are poisonous. Poison sumac is distinguished by the untoothed margins of its leaflets. Poison sumac looks nothing like its two closest relatives, eastern and western poison ivy. Eastern poison ivy is a vine with three leaves. Western poison ivy is a small shrub with three leaves. Poison sumac is a tall shrub or very small tree and has compound leaves with 7 to 13 leaflets.
The saps of poison sumac, western poison ivy, and eastern poison ivy all contain the allergenic urushiol. Not all people are allergic to urushiol, but most can become allergic if they are exposed to it. It usually takes 12 to 48 hours for a rash to develop on a previously sensitized person. In some individuals, a single exposure will cause a reaction. In these individuals, the rash will develop in seven to ten days. The lesions last 14 to 20 days. Rashes do not spread and are not contagious. Treatment can dry the blisters, reduce the swelling, and relieve the itching, but it will not speed the healing.
There are 189 species of Funaria. Only two have been recorded in Minnesota. Bonfire moss (Funaria hygrometrica) is the most abundant species of Funaria and one of the most common and widespread mosses in the world. It frequently occurs in waste areas, and is especially common in recently burned areas and around campfire rings. It is also found in natural areas in swamps, fens, meadows, cattail marshes, and wet prairies. It grows in dense tufts and often forms extensive turfs. The tufts are soft to the touch.
The plant consists of a short leafy stem and a spore capsule at the end of a long slender stalk. The leaves are clustered at the top of the stem forming a rosette. They have only one layer of cells and are almost transparent. The stalks supporting the spore capsule nod at the tip. They readily absorb moisture from humid air, twisting as they do, and becoming entangled with other stalks. The spore capsules are relatively large and appear earlier in the year than those of most mosses. Spores are dispersed late spring to mid-summer.
Pin cherry (Prunus pensylvanica) is a small, fast-growing, short-lived, deciduous tree. It is common from New England to the upper Midwest and across southern Canada, uncommon and scattered west of the Great Plains. It is common throughout Minnesota except for the southwest quarter.
Pin cherry reproduces mostly by root sprouts and often forms thickets. In forests, it rarely germinates, and when it does, the saplings rarely survive except in large openings with plentiful moisture and light. Seedlings mostly appear in a forest after heavy cutting, burning, or a blow down. They mature rapidly and live only 20 to 40 years.
Pin cherry can easily be mistaken for black cherry or American Plum. Unlike black cherry, the bark remains thin and smooth on mature trees; the leaves are yellowish-green, not dark green; the leaf tips are drawn out into a long thin point; and the inflorescence is an umbrella-shaped cluster of 2 to 7 flowers, not a 3″ to 6″ long cluster of 20 to 60 flowers. Unlike American plum, the branches do not have spines, and the inflorescence often has clusters of 5, 6, or 7 flowers.
Japanese hop (Humulus japonicus) is an invasive, prohibited noxious weed in Minnesota. It can form dense mats several feet deep covering and inhibiting the growth of all other vegetation. It is relatively new in the state. The first recorded sighting was in 1992. To date, it has been reported in just four counties in the southeastern corner of the state, and in Hennepin and Scott Counties in the metro area.
Japanese hop closely resembles the native common hop (Humulus lupulus). Japanese hop is distinguished by the leaf stalk that is as long or longer than the blade; the leaf blade that has 5, 7, or 9 lobes and is rough to the touch on the underside; the stiff hairs on the margins of the bracts on the fruiting structure; and the lack of stalked, yellowish glands on the fruiting bracts, anthers, and seed capsules. Also, unlike common hop, the fruiting structure is not fragrant when crushed, and it cannot be used for making beer.
Visitors to Minnesota’s natural places will occasionally come across a stand of Canada thistle with a few plants that are whitened at the top, appearing bleached. The discoloration is caused by the bacterium Pseudomonas syringae pv. tagetis. It has been called “White‐colour Disease of Canadian Thistle,” “apical chlorosis of Canada thistle,” and “Bacterial Speck”, but it has no widely-accepted common name. It is often referred to in scientific literature as Pst.
Outside of a laboratory, a bacterium is recognized only by the symptoms it produces in its host. Pst produces the substance tagetitoxin, which blocks the production of chloroplasts, preventing photosynthesis. This results in whitened plant growth (chlorosis) on only the upper portion of the plant, stunted growth, fewer shoots, and inhibition of flowering. Pst infects plants in the Aster family, including Canada thistle, common dandelion, common sunflower, common ragweed, giant ragweed, Jerusalem artichoke, and some other plants not found in Minnesota.
Researchers at the University of Minnesota conducted a study in 2002 to assess the viability of using Pst as a biological control agent for Canada thistle.
Many species of orchids are found in Minnesota prairies, but only three are prairie specialists: western prairie fringed orchid, Great Plains ladies’ tresses, and small white lady’s slipper. They all occur in lime-rich sediments deposited by glaciers and in clay-rich soils of glacial lake beds.
Small white lady’s slipper (Cypripedium candidum) is widely scattered but uncommon across the Great Lakes states to the Dakotas and adjacent Canadian provinces. Minnesota is the core area of the species and may have more individual plants than all other states and provinces combined. It is found in relatively undisturbed, high-quality prairies in the western, southern, and metro regions of the state.
Small white lady’s slipper produces small flowers that are easily overlooked. The best time to see it in bloom is … right now, the last week of May in southern Minnesota and the first or second week of June in the north.