Arundo donax L.

Fruits are short achenes with long pappus.

New Caledonia: Arundo donax flowers during the cold season, then fructification occurs during the dry season.

Arundo donax forms dense stands on disturbed sites, sand dunes, in wetlands and in riparian zones (banks of watercourses).It refers sandy to loamy soil.

A. donax is a hydrophytic species but it can also develop on many types of wet soils (even those with a certain salinity) and in very diverse climatic and environmental conditions:
- annual rainfall from 300 to 4000 mm.
- annual temperatures from 9 to 29°C
- soil pH from 5 to 8.7

The only two limiting factors seem to be the extreme altitude (although it is found up to 4 000 meters in Ecuador) and the regular periods of frost (too continental climates). It is frequently found in wetlands, along roadsides and on coastal areas.

New Caledonia: Arundo donax appreciates wet and sunny areas, but has a high degree of ecological plasticity. In particular, it supports droughts. It is found in areas with annual rainfall of 1400 to 4000 mm at medium temperatures. It is found spontaneously throughout the Grande Terre, the LoyautéesIslands and the Ile des Pins but preferentially in altitude on the east coast. It develops along rivers. It is also a ruderal species that colonizes roadsides and wasteland. It is found in pasture mostly in small colonies.

Origine

Arundo donax is native to eastern and southern Asia, and probably also parts of Africa and the southern Arabian Peninsula

Worldwide distribution

Arundo donax currently occupies temperate and Mediterranean Europe, Asia to China, South America and Central America, South Africa, Australia and Oceania. Europe (France, Albania, Cyprus, Greece, Hungary, Italy, Portugal, Azores, Spain, Canary Islands, Serbia and Montenegro, Ukraine); Asia (Afghanistan, Azerbaijan, China, India, Iran, Iraq, Israel, Japan, Jordan, Kazakhstan, Laos, Lebanon, Malaysia, Myanmar, Nepal, Pakistan, Republic of Georgia, Saudi Arabia, Sri Lanka, Syria, Tajikistan, Thailand, Turkmenistan, Uzbekistan, Turkey, Vietnan); Introduced throughout the southern United States, Central America, Caribbean and South America. Central America, the Caribbean and South America. The species is also naturalized and invasive in South Africa, Australia and in islands of Oceania (Belau, Cook Islands, Fiji, Guam, New Caledonia, New Zealand, Samoa, Tonga).

It was introduced in New Caledonia in 1883 to stabilize the slopes of roads. In the flora of the Antilles, A. donax is cited as very rare in Martinique and Guadeloupe. It is not mentioned for French Guyana in the Cayenne Herbarium, but is noted present for this region in the Crop Protection Compendium.

Voluntary introduction

Horticultural sector: Arundo donax is cultivated for many uses (ditch erosion control, handicrafts, energy source, pharmaceuticals...), but also as an ornamental plant (several varieties not all of which present a risk of invasiveness) and for the manufacture of clarinet and saxophone reeds.

Unintentional introduction

Very unlikely

Viable forms of the plant: seeds, rhizomes, stem fragments (cuttings)

Environments at risk

Aquatic to humid environments, but also the coastal zones of Reunion Island. In case of installation on the edge of a sugarcane field, having the same habit and a very similar biology, A.donax can compete with the crop in a very important way. It will then be very difficult to specifically control this species without direct damage to the sugarcane.

Global weediness

Arundo donax is regarded as an environmental weed in many parts of the world. It is invasive in parts of South Africa, Australia, and the USA, particularly in Florida and California, where it is a problem in riparian zones (banks of watercourses) and along roadsides. In densely infested areas it has replaced native plants along rivers, such as willows and cottonwoods, thereby interfering with water flow and displacing riverside habitat. Colonies of A. donax covering hundreds of acres have been recorded. It is highly flammable and can change fire regimes in invaded areas, thereby transforming riparian communities of native plants into solid stands of this species.
A. donax has been nominated as among 100 of the "World's Worst" invaders by the IUCN Invasive Species Specialist Group and it has been 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) and in the Australian state of New South Wales.(from BioNET_EAFRINET). The resulting closure of the environment has the following consequences
- the creation of a physical barrier to access to the watercourses;
- a retention of sediments and a progressive reduction of the width of the watercourses (which thus leave their bed much more easily during floods);
- to favour fires (the plant, even green, is highly flammable).

Its root system is also extremely efficient and places this plant at the forefront of the exploitation of soil water resources. This explains its high competitiveness compared to other riparian species. This results in a strong tendency to dry out the environments in which it develops.

Local weediness

Hawaii: the plant has naturalized on coastal areas where it forms large and dense populations.
New Caledonia : Weed of pastures, it is present mostly in small colonies.
South Africa : A. donax is distributed throughout South Africa. Declared as a category 1 weed (CARA 2002 – Category 1 Proposed legislation: NEMBA – Category 1b). A problem throughout South Africa in wetlands. Competes with and replaces indigenous species. It forms very dense stands on riverbanks and in riverbeds which results in the narrowing of water channels, increased siltation and the exclusion of smaller and less vigorous riverbank species.
USA: In Southern California, rivers from the coastal plains to the seashore are completely covered by the plant. It is probable that the infestation started at the end of the sixties after strong storms (propagation by water fragments and rhizomes).

Herbarium pictures ReCOLNAT: https://explore.recolnat.org/search/botanique/simplequery=Arundo%2520donax