Cross shrub

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Cross shrub
Baccharis halimifolia, flowers on a female shrub, with a long pappus

Baccharis halimifolia , flowers on a female shrub, with a long pappus

Systematics
Order : Astern-like (Asterales)
Family : Daisy family (Asteraceae)
Subfamily : Asteroideae
Tribe : Astereae
Genre : Baccharis
Type : Cross shrub
Scientific name
Baccharis halimifolia
L.

The cross shrub , scientific name Baccharis halimifolia , is a shrub of the genus Baccharis from the sunflower family , native to coastal vegetation on the east coast of North America. It was introduced to Europe as an ornamental shrub in the 18th century and is naturalized as a neophyte on the Atlantic coasts of Western Europe . The cross shrub is considered an invasive species in Europe and Australia , and is included in the European Union's list of invasive alien species of Union concern .

description

Foliage leaves

The cross shrub is a shrub, more rarely a small tree , with a stature height of one to three, rarely up to six meters in its North American home, in Europe only up to a maximum of three to four meters. The lignified shoot axes are upright or ascending, usually densely branched from the base, with bark that is smooth or small when young, later longitudinally furrowed to deeply longitudinally fissured, often somewhat sticky due to escaping resin , they reach a diameter of about 16 centimeters. The alternate leaves are sessile or short-stalked, they are multiform in outline, elliptical to obovate on older branches, mostly diamond-shaped on young branches, they are thick and coarse, often a bit glandular and sticky and light green, colored gray-green with age. They are wedge-shaped and with entire margins at the base, usually roughly serrated towards the tip in the leaf margin, they reach about 3 to 5 centimeters in length with 1 to 4 centimeters in width, rarely a little above.

The cross shrub is a dioecious plant, so male and female flowers are on different individuals. It blooms in late summer to autumn with numerous, white-colored heads that appear together with the leaves. The basket-shaped flower heads, which are typical of the daisy family, have few, usually one to five, in terminal or axillary total inflorescences . Each head consists of about 20 to 30 tubular flowers with a corolla about 3 to 4 millimeters long and is surrounded by green, roof-tile-like overlapping bracts . The white colored pappus of the 1 to 2 millimeter long fruits (called achenes or cypsela) is much longer than the flower tube and protrudes long from it.

distribution

The cross shrub grows indigenously in coastal western North America, on the Atlantic coast and in the Gulf Coast Plain , east to Oklahoma and Texas , in Mexico and in the Caribbean (Cuba and Bahamas). The northern limit of the distribution is on Nova Scotia , Canada, where the species is extremely rare and was only discovered in 1998.

The species was introduced by humans into some regions of the world, has become wild there and is now a wild neophyte. Some of these occurrences displace native species there and change the autochthonous vegetation, which is why the species was classified as "invasive". The occurrences in Australia, Queensland and New South Wales are considered invasive, with cross-shrub thickets taking up thousands of hectares here. In New Zealand there is only a small deposit on the Banks Peninsula on the South Island, it is considered to be unproblematic. Little is known about another naturalized occurrence in Abkhazia , on the coast of the Black Sea.

In Europe the species occurs in different regions. The largest deposits are on the coast of the Atlantic from northern Spain ( Biscay ), along the French Atlantic coast to Belgium. In the neighboring Netherlands, only one inconsistent occurrence in the nature reserve De Kwade Hoek , Goedereede was reported in 2003, which could not be confirmed later. From Great Britain there are only two individual records from the English south coast. Occurrences also exist on the coasts of the Mediterranean Sea, from Catalonia along the French Mediterranean coast to northern Italy (Po estuary in Veneto and near Livorno ).

No overgrown occurrences are known in Germany or Austria.

Biology and location

Baccharis halimifolia grows in subtropical to temperate (temperate) climates, it tolerates frosts down to about −15 ° C, but larger occurrences only exist in almost frost-free habitats. Seeds prefer to germinate at 15 to 20 ° C. Due to the late flowering and seed maturity, the species requires a relatively long growing season. The shrub needs permanently well-moistened soils, it prefers salt marsh and other humus soils with a high organic content, but occurs on a variety of soils, from sand to clay and rocky subsoil.

Indigenous occurrences of the cross shrub grow mainly in the middle, tidal marshland , often mixed with the salt-tolerant shrub Iva frutescens . On raw soils and disturbed soils, the species can sometimes settle for a time far from the coast due to its wind-dispersed seeds.

It often grows in locations that have been flooded with brackish water for a long time , such as on the edge of lagoons . Salt contents of up to 1.5% up to 2% in the root space are tolerated without any problems. The cross shrub can withstand full sun, but also grows in the partial shade of other woody plants, where seeds ripen. Especially in northern Spain and southern France, the shrub species penetrates natural vegetation units of the coastal landscape, where salt-tolerant shrubs are naturally lacking. He replaced here reedbed , reeds the beach bulrush , holdings of beach-couch grass ( Elymus athericus ) and salt marshes , he penetrates to seaward in Sarcocornia -Salzwatten ago, but can still strongly influenced by saline samphire -Watten not colonize. The decline in reed beds is proving to be problematic for adapted species such as the rare reed warbler.

Combat

The species is controlled as an invasive neophyte in Australia and Europe. One project was carried out in the Spanish Basque Country, for example, where the cross shrub grows large populations in the brackish water habitats of the estuaries, around more than 300 hectares of bushland in the Urdaibai Biosphere Reserve , one of the most important wetlands in Spain. Here an attempt is made to pull up young plants by hand. Older shrubs are cut off and the cut surface is herbicide treated.

In the European Union, breeding and trade has been banned since 2016 because it was included on the list of invasive alien species of Union-wide importance

In Australia, the rust fungus Puccinia evadens is used for biological pest control against the cross shrub.

Taxonomy

The species was first described by Carl von Linné in his work Species Plantarum in 1753 . It is the type species of the genus Baccharis described by Linné as early as 1737 in the Hortus Cliffortianus , established as such on the basis of a suggestion by the Jena botanist Frank H. Hellwig. A synonym is Baccharis cuneifolia Moench, 1794. Also the Baccharis halimifolia var. Angustior DC described from the Caribbean . is usually no longer recognized today.

Within the very species-rich genus, the species of the subgenus Baccharis s. st. attributed, about 240 species of which are distributed from South America north to southern Canada.

Individual evidence

  1. ↑ Baccharis halimifolia, Sea-myrtle, consumption-weed, eastern baccharis . Scott D. Sundberg & David J. Bogler: 140. Baccharis Linnaeus. Flora of North America Vol. 20, 28.
  2. ↑ a b c d Guillaume Fried, Lidia Caño, Sarah Brunel, Estela Beteta, Anne Charpentier, Mercedes Herrera, Uwe Starfinger, F. Dane Panetta (2016): Monographs on Invasive Plants in Europe: Baccharis halimifolia L .. Botany Letters 163 ( 2): 127-153. doi: 10.1080 / 23818107.2016.1168315
  3. ^ Raymond A. Fielding (2001): Baccharis: a genus of the Asteraceae new to Canada. Proceedings of the Nova Scotian Institute of Science 41 (4): 214-215.
  4. ^ Distribution map , Australasian Virtual Herbarium.
  5. ↑ G. Rappé, F. Verloove, W. van Landuyt, E. Vercruysse (2004): Baccharis halimifolia (Asteraceae) aan de Belgische kust. Dumortiera 82: 18-26.
  6. ↑ Johan JLCH van Valkenburg, Leni H. Duistermaat, Han Meerman (2015): Baccharis halimifolia L. Nederland: waar blijft Struikaster? Gorteria 37: 25-30.
  7. ↑ EPPO (2013): Pest Risk Analysis for Baccharis halimifolia. EPPO European and Mediterranean Plant Protection Organization, Paris. download
  8. ^ Cross shrub (Baccharis halimifolia) . Neobiota portal North Rhine-Westphalia, State Office for Nature, Environment and Consumer Protection North Rhine-Westphalia, last updated on September 18, 2019.
  9. ↑ Baccharis halimifolia - cross shrub . Neobiota in Austria. The influence of alien species on genes, species, and ecosystems. Federal Environment Agency, Department of Biological Diversity & Nature Conservation, Vienna.
  10. ↑ L. Can˜ño, JA Campos, D. García-Magro, M. Herrera (2013): Replacement of estuarine communities by an exotic shrub: distribution and invasion history of Baccharis halimifolia in Europe. Biological Invasions 15: 1183-1188. doi: 10.1007 / s10530-012-0360-4
  11. ↑ J. Arizaga, E. Unamuno, O. Clarabuch, A. Azkona, (2013): The impact of an invasive exotic bush on the stopover ecology of migrant passerines. Animal Biodiversity and Conservation 36 (1): 1-11.
  12. ↑ E. Beteta, L. Oreja, A. Prieto, M. Rozas: Life + Project Estuaries of the Basque Country: control and elimination of Baccharis halimifolia L. in Urdaibai. NEOBIOTA 2012: 7th European Conference on Biological Invasions, Pontevedra (Spain) September 12-14, 2012: Halting Biological Invasions in Europe: from Data to Decisions, Abstracts: 237-238.
  13. ↑ Jim Cullen, Mic Julien, Rachel McFadyen: Biological Control of Weeds in Australia. Csiro Publishing, 2012, pp. 91f.
  14. ↑ Frank H.Hellwig (1989): (953) Proposal to conserve 8933 Baccharis L. (Asteraceae) with a conserved type. Taxon 38: 513-515.