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Canna plants with yellow flowers and detail of seed pods and seeds (Photo: Robert Uyeyama, CC-BY-SA)
Canna fruits, Reunion Island (Photo: BrunoNavez, CC-BY-SA)
Canna plant, Reunion Island (Photo: Bruno Navez, CC-BY-SA)
Canna plant, Uganda (Photo: Geoffrey Howard, IUCN)
Canna invasion, Fort portal, Uganda (Photo: Geoffrey Howard, IUCN)
Canna edulis Ker Gawl.; C. aurantiaca Roscoe; A. barbadica Bouche; C. ammaei Andre
Wild canna lily, canna, Indian shot
Locations within which Canna indica is naturalised include eastern and south-eastern Australia. New Zealand, southern USA, southern and eastern Africa, Hawaii and several other Pacific islands.
Canna indica is invasive in parts of Kenya and Uganda (A.B.R. Witt pers. obs.) and Tanzania (Henderson 2002, Global Invasive Species Database).
Swamp and wetland edges, streambanks and other moist areas. Sometimes also found growing in old gardens, disturbed sites and waste areas.
The upright (erect) stems (1-2 m tall) are sturdy, hairless (glabrous) and green in colour. The alternatively arranged leaves consist of a stem-clasping sheath at the base and very large, spreading, leaf blade (20-60 cm long and 10-30 cm wide). The leaf blades are elongated or oval (elliptic) in shape but come to a point at the tip (they have acute or acuminate apices). They are hairless (glabrous), have entire margins, and narrow at the base where they join to the top of the leaf sheath.
The flowers can be either red, yellow or occasionally red and yellow (yellow with red spots or vice versa) and are quite showy. They are borne singly or in pairs (monochasial cymes) and arranged into larger branched clusters (with 6-20 flowers) at the tips of the flowering stems. Each flower appears to have five 'petals' but these are actually other floral structures (staminodes and petaloid filaments) that have become modified to imitate petals. The petals are actually the three bract-like structures below these false 'petals' (4-6.5 cm long and 0.4-0.7 cm wide). They are fused together at the base (into a perianth tube 5-15 mm long) and their margins are curved inwards. Each flower has three slightly different types of false 'petals' (three outer staminodes, an inner staminode and a petaloid filament). The three outer staminodes are relatively broad (3.5-6 cm long and 0.5-1.5 cm wide) while the inner staminode (labellum) is usually somewhat narrower (up to 4-5 cm long and 0.8 cm wide) with its tip bent backwards (it has a recurved apex). The single petaloid filament is narrower again (3-4 mm wide) and has an anther about 10 mm long about half way up one of its sides. Each flower also has three narrow sepals (9-17 mm long and 2-5 mm wide) and their bases are also surrounded by a floral bract (5-30 mm long and 5-15 mm wide) and bracteoles (5-20 mm long and 3-8 mm wide).
The papery capsules (1.5-3 cm long and 1.5-2 cm wide) are oval (ellipsoid) to almost rounded (sub-globose) in shape and are crowned by the persistent sepals. They are initially green or purplish in colour and covered in numerous short projections (they are verrucose), but turn brown as they mature and may lose some or all of their tiny projections. They split open at maturity to release numerous smooth, black, rounded (spherical) or egg-shaped (ovoid) seeds. These seeds are relatively large (5-8 mm long and 4-7 mm wide) and very hard.
This species reproduces by seed and vegetatively via its fleshy underground stems (rhizomes). The seeds are thought to be dispersed by birds, while the seeds and rhizomes may also be spread by floods and in dumped garden waste.
Canna indica is very similar to the garden cannas (Canna x generalis and Canna x orchiodes). These species can be distinguished by the following differences:
Cannas are popular cultivated flowers in tropical and temperate gardens and there are many cultivated varieties. They come in beautiful and exotic yellow, orange, pink or red blossoms, sometimes with spots or flames on it. The blossoms of the cultivated varieties are much bigger than those of Canna indica (Bourne et al.1988). They come in many colours while the flowers of the wild-growing Canna only come in red and yellow. The seeds are used in jewellery such as bracelet and earrings. However, these uses cannot compensate for this plant's overall negative impacts.
Canna indica forms large dense clumps, particularly in riparian zones (banks of watercourses), and replaces native freshwater and wetland species. It can restrict water movement, cause flooding, and limit access to waterways. In Hawaii and Fiji it also becomes naturalised in disturbed wetter forests and in forest clearings. In Hawaii it also a weed of plantation crops (e.g. coconut).
C. indica is regarded as an invasive species in other parts of the world such as Australia and many Pacific islands. It is listed in the Global Invasive Species Database (GISD 2011). It is listed as a noxious weed in South Africa is listed as a noxious weed in South Africa (prohibited plants that must be controlled. They serve no economic purpose and possess characteristics that are harmful to humans, animals or the environment).
The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species. Some components of an integrated management approach are introduced below.
The best form of invasive species management is prevention. If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Controlling the weed before it seeds will reduce future problems. Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.
Small plants can be uprooted but it is important to remove the roots completely as Canna indica reproduces vegetatively from rhizomes. Usually digging or herbicide spraying will be required. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.
Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.
Germplasm Resources Information Network (GRIN). www.ars-grin.gov/npgs/index.html. National Germplasm Resources Laboratory, National Genetic Resources Program, Agricultural Research Service (ARS), United States Department of Agriculture (USDA), Beltsville, Maryland, USA. Accessed March 2011.
Henderson, L. (2001). Alien weeds and invasive plants. A complete guide to declared weeds and invaders in South Africa. Plant Protection Research Institute Handbook No. 12, 300pp. PPR, ARC South Africa.
Henderson, L. (2002). Problem plants in Ngorongoro Conservation Area. Final Report to the NCAA.
Henderson, L. and Cilliers, C.J. 2002. Invasive aquatic plants-a guide to the identification of the most important and potentially dangerous invasive aquatic and wetland plants in South Africa. PPRI Handbook No. 16, Agricultural Research Council, Pretoria.www.arc.agric.za/uploads/images/0_SAPIA_NEWS_No._17.pdf.
Pacific Island Ecosystems at Risk (PIER). Canna indica L., Cannaceae: plant threats to Pacific ecosystems. www.hear.org/Pier/species/canna_indica.htm. Institute of Pacific Islands Forestry, Hawaii, USA. Accessed March 2011.
USDA Plants Profile. Canna indica L. Indian shot. Plants Profile. plants.usda.gov/java/profile?symbol=CAIN19. National Plant Data Center, National Resources Conservation Service, United States Department of Agriculture, Baton Rouge, Louisiana, USA. Accessed March 2011.
Agnes Lusweti, National Museums of Kenya; Emily Wabuyele, National Museums of Kenya, Paul Ssegawa, Makerere University; John Mauremootoo, BioNET-INTERNATIONAL Secretariat - UK.
This fact sheet is adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland. We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).
BioNET-EAFRINET Regional Coordinator: firstname.lastname@example.org