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Saturday, 24 January 2015

Invasive plant species in the South-East of England

These species are all listed on Schedule 9 of the Wildlife and Countryside Act (1981) as amended. Here are some identification features of these invasives in Britain. This may be quite dry without pictures so probably best to just use it for a reference guide! Please note that these only include species found in the south-east of England and exclude marine species.

Terrestrial species


Japanese Knotweed Fallopia japonica

-Large (to 16cm length), cordate leaves with points.
-Alternate, leaves growing on stalks.
-Zig-zag hollow stems to 2m tall.
-Small white flower spike (July-Autumn).
-Disturbed and waste ground.


Giant Knotweed Fallopia sachalinensis
-Similar to Japanese Knotweed but larger.
-Grows taller than 2m (to 5m tall).
-Cordate leaves growing to lengths of 30cm.


Himalayan Balsam Impatiens glandulifera
-Oval-lanceolate leaves (to 15cm length) with serrated edges, on stalks.
-Leaves in whorls of three or opposite on stem. Near the terminal bud leaves are often arranged singly.
-Hairless stems (to 2m height), which thicken at nodes.
-Large, pink flowers (June to October).
-Wasteland or river banks in British lowlands.


Giant Hogweed Heracleum sphondylium
This species is often confused with Common Hogweed Heracleum sphondylium. However there are multiple differences outlined below. In each point Giant Hogweed characteristics are first, with differences of Common Hogweed following:
-Grows to 5m height (in 4th year), however Common Hogweed grows to 2m tall.
-Red-spotted stems to 10cm wide with fine spines that make it appear furry however Common -Hogweed stems are hairy but without red spots and are narrower than those of Giant Hogweed.
-Leaves to 1m long (and 1.5m wide) however Common Hogweed leaves to 50cm long.
-Leaves also 3-times pinnate but with sharper teeth. Common Hogweed leaves are 3-times pinnate with blunt teeth.
-Flower head to 50-150cm across however Common Hogweed flower head (from June) grows to just 15cm diameter.
-Found on lowlands, on disturbed ground especially by rivers. Common Hogweed grows on .grassland, scrub, hedgerows, and riverbanks


Wall Cotoneaster Cotoneaster horizontalis
-Most common introduced Cotoneaster species.
-Deciduous shrub.
-Horizontal stems with a 'herring bone' branch pattern, flat to one plane.
-Alternate leaves (just 0.6-1.2cm long) are shiny and flat on upperside, and near hairless below.
-Common on rocky grassland, pavements, and wasteland. Often found appressed to vertical walls.


Small-leaved Cotoneaster Cotoneaster microphyllus
-Prostrate evergreen shrub growing to just 1m in height
-Upperside of leaves are shiny and flat, lowerside have appressed hairs
-Alternate leaves are typically just 0.5-0.8cm in length (but to 1.2cm).


Entire Leaved Cotoneaster Cotoneaster integrifolius

-Evergreen shrub to 2m in height.
-Leaf upperside is shiny, whereas underside is covered with soft, appressed short hairs.
Mature leaf length of 0.7-1.5 cm, and leaves are oblanceolate to oblong or obovate.
-Has typically longer leaves than Small-leaved Cotoneaster Cotoneaster microphyllus, and also larger berries of 7-10mm diameter compared to 5-8mm of Cotoneaster microphyllus.


Himilayan Cotoneaster Cotoneaster simonsii

-Upright evergreen shrub.
-Leaf upperside is shiny and flat, whereas the underside has sparse hairs (short and soft).
-Alternate leaves.
-Mature leaf is 1.5-3cm in length and broadly ovate.


Hollyberry Cotoneaster Cotoneaster bullatus

-Deciduous shrub growing to 4m tall.
-Alternate leaves (3.5-7cm in length) are shiny and with deep vein indentations on upperside, and quite densely hairy on underside.
-Bright, shiny red fruits ~6-8mm diameter, obovate (narrower end near the stalk) to sub-globose (squashed sphere) with 4-5 stones.


Rhododendron Rhododendron ponticum
-Evergreen shrub to 5m tall. Be careful not to confuse with Laurel species which has smaller leaves, which are sometimes toothed.
-Leaves 6-20cm in length, hairless on both sides, ~flat, elliptic to oblong
-Sandy and peaty soil, rocks in woods and open places.


Great Rhododendron Rhododendron ponticum x Rhododendron maximum

-Leaves hairy on lowerside.
-Very shade tolerant and is usually found in low-lying heavily wooded areas on moist, acidic soils.


Virginia Creeper Parthenocissus quinquefolia
-Deciduous vine with woody stem.
-Compound leaves, containing five leaflets, each 5-15cm long with slightly toothed margins.
-May climb buildings or walls, or trail along the ground.


False Virginia Creeper Parthenocissus inserta
-Differs from Virginia Creeper in leaves more acutely serrate.
-Narrow tendrils not ending in enlarged adhesive discs like in Virginia Creeper.
-Much rarer than Virginia Creeper.


Variegated Yellow Archangel Lamiastrum galeobdolon subsp. argentatum

-Creeping perennial, a.k.a “Yellow Dead-nettle”.
-Has hairy, toothed leaves.
-Upright stems (to 30cm) also finely hairy.
-Yellow flowers in whorls around the stem.
-Native Yellow Archangel Lamium galeobdolon has all-green leaves, whereas the introduced Variegated Yellow Archangel Lamium galeobdolon ssp. argentatum, has silvery blotches on leaves.
-Damp soil and partial shade.


False Acacia Robinia pseudoacacia

-A spiny tree up to 29m height.
-Pinnate compound leaves, with 5-11 opposite pairs of leaflets.
-Numerous white, pea-like flowers subsequently producing 3-10 seed-pods.
-Infrequent in semi-natural habitats in Britain, but colonises brownfield sites and urban waste ground.


Perfoliate Alexanders Smyrnium perfoliatum

-Rounded stem-leaves lack stalks, and are deeply cordate so that they encircle the stem.
-Basal leaves are 2-3 times pinnate.
-Stems erect, typically to 60 (but sometimes 100)cm.
-Flower heads are delicate yellowish green umbels.


Three-cornered Garlic Allium triquetrum

-Leaves sharply keeled on underside, yet have semi-circular indentation running along the centre of the upperside of the leaf.
-Leaves are 4-12mm wide (typically narrower than Few-flowered Leek and Ramsons), 2-5 per bulb.
-Hollow triangular stem, with three concave sides.
-To 45cm in height, with white flowers.


Few-flowered Garlic Allium paradoxum

-Typically one leaf per plant.
-Leaf is flat to scarcely keeled and 5-25mm in width (typically wider than Three-cornered Garlic, but narrower than Ramsons).
-Stems (to 40cm tall) also triangular in cross-section.
-Produces white bulbils with or without flowers (most commonly only with 1 flower).


Montbretia Crocosmia x crocosmiiflora

-Lanceolate, leaves are 30-80cm long and 1-3cm wide, sheath the stem (to 60cm tall)
-Tubular, red six-petalled flowers 3-4cm long  in elongated clusters at top of stems
-Hybrid of Crocosmia aurea and Crocosmia pottsii. Other Crocosmia sp. are rarely found in the wild and tend to not behave in an invasive manner.
-Gardens, naturalised in hedgerows, woods, by lakes and river, on waste ground.


Japanese Rose Rosa rugosa

-Erect stems to 1.5m (sometimes 2m), covered in felt-like hairs, with many slender thorns.
-5-9 (typically 7) leaflets (8-15cm long) which are shiny with deep vein indentations on upperside, and hairy on lowerside.
-White-red flowers (6-9cm across).
-Common in gardens, parks and amenity areas.



Freshwater invasive species



Floating Pennywort Hydrocotyle ranunculoides

-Characteristic leaves and growth form.
-Shiny, kidney-shaped leaves with crinkled edge, frequently broader than long.
-Grows horizontally
-Emergent or floating on the surface of still or slowly moving freshwater.
-Free-floating or rooted.


Parrot's Feather Myriophyllum aquaticum

-Shoots typically emerge from the water (whereas native species of Water-milfoil are submergent).
-Feather-shaped leaves are densely covered with blue-green, stalkless glands (unlike Whorled Water-milfoil - sparse glands and Spiked or Alternate Water-milfoil which lack glands).
-White flowers are arranged in whorls of 4-6.
-Fresh water in reservoirs and canals, ditches and ponds.


Australian Swamp Stonecrop Crassula helmsii

-Perennial with fleshy, opposite linear-lanceolate leaves of 4-20mm length sometimes fusing together around stem.
-Tiny, white flowers (June to September).
-Stems (to 30cm) either trailing in water, ascending from it or growing from mud.
-Will grow in water up to 3m deep.


Australian Stonecrop in Epping Forest

Fanwort Cabomba caroliniana
-Opposite, fan-like leaves to ~5cm across.
-Tubular stems to lengths of 1.8m.
-Flowers typically white-cream (although some are pink-purple) and to 1.5cm wide (May-September).
-Grows underwater, although small oval or diamond-shaped floating leaves may develop.
-Prefers lakes and ponds, and occasionally rivers.


Water Fern Azolla filiculoides

-Forms floating rosettes of branched, overlapping leaves (to 2.5cm long) with non-wettable surface and rough, granular appearance.
-Black-brown roots from beneath floating leaves, easily break off.
-Initially green, becoming reddish late in the season.
-Duckweed leaves just 1.5-4mm across and are not branched. Also have a white-green root attached to each leaf.
-Ponds, lakes, and slow flowing rivers.


Water Hyacinth Eichhornia crassipes

-Free-floating perennial plant growing to a height of 1m.
-The circular to elliptical leaves are attached to spongy, inflated leaf stalks.
-Striking light blue to violet flowers located on a terminal spike.


Water Lettuce Pistia stratiotes
-Fleshy leaves, which are velvety-hairy with parallel veins.
-Leaves form rosettes to 15cm across, resembling floating lettuce-heads, and produce long roots (up to 50cm).
-Floating stems link rosettes of leaves.
-Still or slowing-flowing water, but can survive in mud.


Water primrose Ludwigia grandiflora

-Vertical stems (to 1m+), and long horizontal stems.
-Alternate leaves (to 13cm length) on emergent stems. (round-oval in Spring, narrowly-elliptic in Summer).
-Rounded leaves on horizontal stems, forming floating rosettes.
-One large, yellow flower per stem (July to August).
-Floating in still/slow-flowing water or terrestrially in marginal mud.



Waterweeds/Pondweeds of the Elodea Genus

-Elodea sp. leaves are stalkless and minutely serrated.
-Lower leaves are usually opposite.
-Upper leaves are in whorls of 3-5.
-Stems are long (to 3m) branched.
-Grow as submerged plants, which are rooted in mud.


Canadian Waterweed Elodea Canadensis
-Leaf tips (apices) obtuse – more rounded leaf tips than other two invasive Elodea sp.
-Oblong-linear leaves 6-23mm long, arranged in whorls of 3, leaves are 1.5-4mm broad.

Other two invasive Elodea sp. have pointed leaf tips 

Nuttall’s Waterweed Elodea nuttallii
-Some leaves strongly recurved,
-Leaves narrow in width (1.5 mm).
-Marginal leaf teeth 0.05-0.1mm

South American Waterweed Elodea callitrichoides 
-Leaves (to 25 mm long and 2-5mm width) and never strongly recurved.
-Tooth's of leaves usually 0.1-0.15mm


Curly Waterweed Lagarosiphon major
-Also long, branched stems (to 3m).
-Leaves are mostly spirally arranged up stem (although sometimes in whorls like Elodea sp.).
-The lowest leaves always spiralled (not opposite like those of Elodea sp.).
-Strongly recurved leaves are closely packed together.
-Also grows as submerged plant, rooted in mud.


References
Averis, B. (2013). Plants and Habitats: An Introduction to Common Plants and Their Habitats in Britain and Ireland

https://www.gov.uk/

http://jncc.defra.gov.uk/default.aspx?page=5431


http://www.nonnativespecies.org/home/index.cfm


Rose, F. and O'Reilly, C. (2006). The Wild Flower Key (Revised Edition) - How to identify wild plants, trees and shrubs in Britain and Ireland. Warne.


Stace, C. (2013). New Flora of the British Isles. Cambridge University Press, Cambridge.

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