Acacia karroo Hayne, Fabaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Other Latin names:  Acacia dekindtiana A. Chev.

Common name(s): [more details]

English: Cape thorn tree, karoo thorn, mimosa thorn, sweet-thorn, white-thorn

Habit:  tree

Description:  "Tree (1.5) 3-15 m. high, rarely shrubby; bark on trunk dark-red-brown to blackish; young branchlets glabrous or rarely sparsely and inconspicuously puberulous, also with small inconspicuous pale to reddish sessile glands; epidermis flaking off to expose a dark-rusty-red not powdery under-bark, sometimes grey to brown and persistent. Stipules spinescent, up to 7 (17) cm. long, rather robust, whitish, often ± deflexed, sometimes fusiform-inflated, up to 1 cm. (? or more) thick, but remaining distinct to the base and not confluent; other prickles absent. Leaves with a small to large (sometimes paired) gland at the junction of each pinna-pair, rarely lacking at the basal 1-2 pairs; sometimes a large gland on the upper side of the petiole; pinnae (1) 2-7 (9) pairs; leaflets 5-15 (27) pairs, 4-7 (12) x 1-3 (5.5) mm., glabrous or rarely with minutely ciliolate margins, eglandular, obtuse to subacute but not spinulose-mucronate at the apex; lateral nerves invisible beneath. Flowers deep- or golden-yellow, in axillary pedunculate heads 8-12 mm. in diameter borne along shoots of the current season, sometimes aggregated into ± leafless terminal "racemes"; involucel c. 1/3-3/4-way up the peduncle, c. 2 mm. long. Calyx 1.25-2 mm. long, subglabrous. Corolla c. 2.5-3 mm. long, glabrous or almost so. Pods dehiscent, (4) 6-16 x 0.6-0.9 (1) cm., linear, ± falcate, usually ± constricted (sometimes not) between the seeds, glabrous except for small usually inconspicuous glands. Seeds olive-green to -brown, 5-8 x 3-5 mm., oblong-elliptic, compressed; areole 4.5-5.5 x 2-3.5 mm"  (Flora Zambesiaca).

"Arbuste à petit arbre de 2 à 10 m de hauteur, pouvant atteindre 25 m dans sa région d’origine, reconnaissable à la paire de longues épines de 1 à 2,5 cm de long, de longues gousses de 16 cm de long sur 1 cm de large comprimées au niveau des graines"  (Meyer, 2008; p. 30).

Habitat/ecology:  "A pioneer species with a climax of 40 years, it occupies a successional position between the tropical forest and the bushveld. It grows in riverine communities and even in arid environments, where it can do well provided there is an assured supply of groundwater. Large specimens are an indicator of underground water. A. karroo is included in the national weed list in South Africa. It competes for space, water and nutrients with pasture grasses, thus replacing them. Sweet thorn is frost- and drought-tolerant. Altitude: 0-1 000 m, Mean annual temperature: 12-40 deg. C, Mean annual rainfall: 200-1 500 mm Soil type: Prefers heavy black, hydromorphic cracking vertisols with high pH, deep alluvial clay-loam soils in river valleys and sometimes on shale and even on acid soils"  (Agroforestree database).  "Woodland, wooded grassland, coastal scrub, often by rivers and in valleys near sea-level to 1520 m"  (Flora Zambesiaca).

Propagation:  Seed.  "Buried seeds of A. Karroo remain viable for up to seven years"  (du Toit, 1972, cited in Csurhes & Edwards, 1998).

"Les graines sont disséminées par le vent, les rivières et les animaux. Elle est extrêmement envahissante en Australie"  (Meyer, 2008; p. 30).

Native range:  Southern Africa (GRIN).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Chile (offshore islands) Rapa Nui (Easter) Island	Rapa Nui (Easter) Island (Isla de Pasqua)	introduced invasive	Meyer, Jean-Yves (2008) (pp. 30-31) cf. Acacia karroo
French Polynesia Society Islands	Tahiti Island	introduced cultivated	Florence, J./Chevillotte, H./Ollier, C./Meyer, J.-Y. (2011) Cultivée

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	New South Wales	introduced	ILDIS Co-ordinating Centre (2011)
Australia Australia (continental)	Queensland	introduced	ILDIS Co-ordinating Centre (2011)

Indian Ocean
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Mauritius Mautitius Islands (Mauritius and Rodrigues)	Mauritius Island	introduced	ILDIS Co-ordinating Centre (2011)

Control:  La lutte manuelle par arrachage des plantules et coupe des arbustes associée à une lutte chimique par traitement des souches avec un herbicide (à base de triclopyr et/ou dicamba) sont réalisables.

Additional information:
Weed Management Guide from the Government of Australia. (PDF format).
Weed identification guide from Weeds Australia.
Fact sheet from the Agroforestree database.

Additional online information about Acacia karroo is available from the Hawaiian Ecosystems at Risk project (HEAR).

Information about Acacia karroo as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

Taxonomic information about Acacia karroo may be available from the Germplasm Resources Information Network (GRIN).

References:

Florence, J./Chevillotte, H./Ollier, C./Meyer, J.-Y. 2011. Base de données botaniques Nadeaud de l'Herbier de la Polynésie Française (PAP). (online resource).

ILDIS Co-ordinating Centre. 2011. International Legume Database & Information Service. Online searchable database.

International Center for Research in Agroforestry. 2008. AgroForestryTree database: a tree species reference and selection guide (online resource). World Agroforestry Centre.

Meyer, Jean-Yves. 2008. Rapport de mission d'expertise a Rapa Nui du 02 au 11 Juin 2008: Plan d'action strategique pour lutter contre les plantes introduites envahissantes sur Rapa Nui (Île de pâques) [Strategic action plan to control invasive alien plants on Rapa Nui (Easter Island) [unpublished report]. Délégation à la Recherche, Ministère de l'Education, l'Enseignement supérieur et la Recherche, B.P. 20981 Papeete, Tahiti, Polynésie française. 62 pp. .

U.S. Dept. Agr., Agr. Res. Serv. 2011. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.