Buckthorn

Common buckthorn (Rhamnus cathartica) was first brought to Minnesota from Europe in the mid-1800s as a very popular hedging material. Shortly after its introduction here, it was found to be quite invasive in natural areas. The nursery industry stopped selling it, but many buckthorn hedges may still be found in older neighborhoods throughout Minnesota.

Glossy buckthorn (Frangula alnus), also from Europe, has been sold by the nursery trade in three different forms. The cultivar Columnaris has a narrow and tall form; the cultivars Aspenifolia and Ron Williams have narrow leaves that give them a fern-like texture. This buckthorn aggressively invades wetlands including acidic bogs, fens and sedge meadows.

Ecological Threat:
Out-competes native plants for nutrients, light, and moisture
Degrades wildlife habitat
Threatens the future of forests, wetlands, prairies, and other natural habitats
Contributes to erosion by shading out other plants that grow on the forest floor
Serves as host to other pests, such as crown rust fungus and soybean aphid
Forms an impenetrable layer of vegetation
Lacks “natural controls” like insects or disease that would curb its growth

Non-native bush honeysuckles (Lonicera tatarica, L. morrowii, L. x bella, L. maackii)

Appearance:Upright deciduous shrubs, 5 -12′ high. Bell’s honeysuckle (Lonicera x bella) is a horticultural hybrid. Older stems have shaggy bark and are often hollow.
Leaves: Opposite, simple, oval, and untoothed. Tartarian (L. tatarica) has smooth, hairless leaves, Morrow’s honeysuckle (L. morrowii) has downy leaves. Amur honeysuckle (L. maackii) leaves come to a long, sharp point.
Flowers: Fragrant, tubular, bloom in May and June, white, red, but most often pink.
Fruit: Fruits are red or yellow, situated in pairs in the leaf axils.
Roots: Roots are fibrous and shallow.

Ecological Threat:
Exotic honeysuckle replace native forest shrubs and herbaceous plants by their invasive nature and early leaf-out. They shade out herbaceous ground cover and deplete soil moisture.
Seeds are readily dispersed by birds.
Some research suggests that the plant inhibits the growth of other plants in its vicinity.
Introduced to North America as ornamental shrubs and beneficial to wildlife. Commercial propagation continues with many cultivars available from nurseries.
Bell’s, Morrow’s, Tartarian, and Amur honeysuckles are MDA Restricted noxious weeds  in Minnesota.

Garlic mustard (Alliaria petiolata)

Appearance: Biennial herbaceous plant with weak single stems 12 – 36″ high in its second and flowering year. Only plant of this height blooming white in wooded environments in May.
Leaves: Round, scallop-edged, dark green; first year, rosettes of 3 or 4 leaves; second year plants have alternate stem leaves. Leaves and stems smell like onion or garlic when crushed.
Flowers: White, small and numerous, with four separate petals. Each plant has one or two flowering stems on second year plants.
Seeds: Slender capsules 1-2 1⁄2″ long, containing a single row of oblong black seeds. Seeds are viable in the soil for 5 years.
Roots: White, slender taproot, “S”-shaped at the top.

Ecological Threat:
•Garlic mustard spreads into high quality woodlands upland and floodplain forests, not just into disturbed areas.
•Invaded sites undergo a decline on native herbaceous cover within 10 years.
•Garlic mustard alters habitat suitability for native insects and thereby birds and mammals.
•This European exotic occurs now in 27 midwestern and northeastern states and in Canada.
•Garlic mustard is a MDA Restricted noxious weed in Minnesota.