Species Identification

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How To Identify Five Common Invasive Species

There is no substitute for getting outside and actually looking at these plants to acquire a good idea of their distinguishing charatcteristics. However, below is some of the best information available for these species that was provided by the Invasive Plants Association of Wisconsin (also available on their website). Images and information are from the Invasive Plants Association of Wisconsin (IPAW), the Plant Conservation Alliance (PCA) Alien Plant Working Group (Weeds Gone Wild), the USDA PLANTS database, Wikipedia, or other available web resources. They are provided to illustrate key identification characteristics. Information is focused on identification features, not invasion history. The five species we will focus on include:

  • Common buckthorn (Rhamnus cathartica)
  • Glossy buckthorn (Rhamnus frangula)
  • Honeysuckle (Lonicera spp.)
  • Garlic Mustard (Alliaria petiolata)
  • Dame's Rocket (Hesperis matronalis)
  • Asian bittersweet (Celastrus orbiculatus)

 

Common buckthorn (Rhamnus cathartica)

Common buckthorn (Rhamnus cathartica) is a serious invader of Wisconsin's wooded areas. It also commonly invades hedge rows of open fields, from which it may gradually spread throughout a whole field. Both common and glossy buckthorn are small deciduous trees or shrubs that can reach a height of 20-25 feet and have a trunk up to 10 inches wide. It most often grows as a shrub, and may send out several shoots. The crown shape of mature plants is spreading and irregular.

The bark is gray to brown, rough textured when mature and may be confused with that of plum trees in the genus Prunus. When cut, the inner bark is yellow and the heartwood pink to orange. They are distinctive in winter with naked, hairy terminal buds and curving or arched twigs with closely spaced and prominent leaf scars that make the twigs look bumpy.

Twigs are often tipped with a spine. In spring, dense clusters of 2 to 6, yellow-green, 4-petaled flowers emerge from stems near the bases of leaf stalks. Male and female flowers are borne on separate plants. Leaves are broadly oval, rounded or pointed at the tip, with 3-4 pairs of upcurved veins, and have jagged, toothed margins. The top and bottom of the leaf are hairless. Leaves appear dark, glossy green on the upper surface and stay green late into fall, after most other deciduous leaves have fallen, but do eventually turn yellow. They are arranged somewhat variably in opposite to subopposite pairs or alternately. Small black fruits about 1/4 inch in cross-section and containing 2-4 seeds, form in the fall.

Species Identitification

Species Identitification

Species Identitification

Species Identitification

Look Alikes:

Several native American buckthorns that occur in the eastern U.S. that could be confused with the exotic species. If in doubt, consult with a knowledgeable botanist to get an accurate identification. Carolina buckthorn (Rhamnus caroliniana), is a lovely native shrub that has finely toothed leaves somewhat resembling those of black cherry, and are smooth on the underside; it produces attractive fruits from August to October. Alder buckthorn (Rhamnus alnifolia), is a low-growing shrub that may grow to a maximum of 3 feet in height, and has leaves with 6-7 pairs of veins

 

 

Glossy buckthorn (Rhamnus frangula)

Glossy buckthorn (Rhamnus frangula) is a similar serious invaders of Wisconsin's wooded areas. To differentiate it from Common buckthorn, note that Glossy buckthorn does not have a spine at twig tips, leaves are not toothed, and the undersides of the leaves are hairy!

Species Identitification

Species Identitification

 

 

 

Honeysuckle (Lonicera spp.)

There are several species of honeysuckle that cause problems in Wisconsin natural areas, but there is no reason to classify them since they are all nonnative and they are all bad. The native honeysuckles in most of Wisconsin can easily be distinguished from the bad ones because the natives are mostly woody vines rather than bushes. The exception is in northwestern Wisconsin where the native fly honeysuckle is an abundant understory shrub in wet mesic sites. Bush honeysuckles are upright shrubs ranging from a few feet to 15 feet tall. They form many branches from the base, and the spreading branches shade other plants.

From a distance...

From a distance, bush honeysuckle appears as a thicket.

Species Identitification

Species Identitification

Closer Up...

Notice the large white flowers with distinctively yellow anthers. The leaves are opposite, simple oval, 1–10 cm long; most are deciduous. Many of the species have sweetly-scented, bell-shaped flowers that produce a sweet, edible nectar. Breaking of the Honeysuckle's stem will release this powerful sweet odor.

Species Identitification

Species Identitification

Links...

IPAW Factsheet
PCA Plant Conservation Alliance Factsheet - Japanese honeysuckle
USDA Factsheet - Japanese honeysuckle
USDA PLANTS Species profile - Japanese honeysuckle
WDNR - Japanese honeysuckle

 

 

Garlic Mustard (Alliaria petiolata)

It is a herbaceous biennial plant (sometimes an annual plant) growing from a deeply growing, thin, white taproot that is scented like a horse-radish. Plants grow from 30-100 cm (rarely to 130 cm) tall. The leaves are stalked, triangular to heart-shaped, 10-15 cm long (of which about half being the petiole) and 2-6 cm broad, with a coarsely toothed margin. In biennial specimens, first-year plants appear as a rosette of green leaves close to the ground; these rosettes remain green through the winter and develop into mature flowering plants the following spring. The flowers are produced in spring and summer in button-like clusters. Each small flower has four white petals 4-8 mm long and 2-3 mm broad, arranged in a cross shape. The fruit is an erect, slender, four-sided pod 2-7 cm long, called a silique, green maturing pale grey-brown, containing two rows of small shiny black seeds which are released when the pod splits open. .

From a distance...

Second year plants look like a thick, tall carpet of very green plants often dotted with white flowers when in seed. The plant typically appears as distinct patches in shaded or moist areas.

Species Identitification

Closer up...

Upon further examination, leaf surfaces appear crinkled, and for second year plants after flowering, the long seed pods (siliques) are obvious and stick out at abrupt angles at the tops of stalks. First year plants form attractive clumps of round shaped, slightly wrinkled leaves, that when crushed smell like garlic.

Species Identitification

Flowers...

The flowers are soft white and have four petals like all mustard plants positioned in a "crucifix" or cross indicative of the old latin name for the mustard fanily (Crucifereae).

Species Identitification

Species Identitification

Leaves of first year plants...

Clusters of 3-8 rounded to kidney-shaped leaves develop at ground level during the first growing season. The leaves have scalloped edges, a wrinkled appearance, and remain green all winter. Note oak leaves for size comparison.

Species Identitification

Species Identitification

Late Summer, Fall, and Winter...

Plants die and seeds are dispersed in July or August. Dry stalks often remain standing through winter.

Species Identitification

Look Alikes...

  • Violet
    • leaves resemble first-year plants, but flowers bloom low and have 5 petals; leaf surfaces are less crinkly and there is no taproot.
  • Ground ivy (creeping Charlie)
    • spreads along the ground as a vine and has purple flowers.

Links...

IPAW Factsheet
PCA Plant Conservation Alliance Factsheet
USDA Factsheet
WDNR Factsheet

 

 

Dame's Rocket (Hesperis matronalis)

Hesperis matronalis grows 100cm or taller, with multiple upright hairy stems. Typically the first year of growth produces a mound of foliage and flowering occurs the second year, plants are normally biennials but a number of races can be short lived perennials. The plants have showy blooms in early to mid spring. The leaves are alternately arranged on upright stems and lanceolate shaped, they typically have very short or lack petioles and have toothed margins but sometimes are entire, they are widest at the base. The foliage has short hairs on the top and bottom surfaces that give the leaves a somewhat rough feel. The larger leaves are around 12cm long and over 4cm wide. In early spring, a thick mound of low growing foliage is produced, during flowering the lower parts of the stems are generally unbranched and denuded of foliage and the top of the blooming plant might have a few branches that end in inflorescences. The plentiful fragrant flowers are produced in large showy terminal racemes, that can be 30+cm tall, that elongate as the flowers of the inflorescence bloom. When stems have both flowers and fruits, the weight sometimes causes the stems to bend. Each flower is large (2 cm across), with four petals. Flower coloration varies, with different shades of lavender and purple most common, but white, pink, and even some flowers with mixed colors exist in cultivated forms. The four Petals are clawed and hairless. The flowers have six stamens in two groups, the 4 closest to the ovary are longer than the two oppositely positioned. Stigmas are two-lobed. The four sepals are erect and form a mock tube around the claws of the petals and are also colored similarly to the petals.

Species Identitification

Species Identitification

Species Identitification

 

 

 

Asian Bittersweet (Celastrus orbiculatus)

Oriental bittersweet is a deciduous woody perennial plant which grows as a climbing vine and a trailing shrub. Stems of older plants 4 inches in diameter have been reported. The leaves are alternate, glossy, nearly as wide as they are long (round), with finely toothed margins. There are separate female (fruiting) and male (non-fruiting) plants. Female plants produce clusters of small greenish flowers in axillary clusters (from most leaf axils), and each plant can produce large numbers of fruits and seeds. The fruits are three-valved, yellow, globular capsules that at maturity split open to reveal three red-orange, fleshy arils each containing one or two seeds. The abundance of showy fruits have made Oriental bittersweet extremely popular for use in floral arrangements.

Species Identitification

 


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