Alligator Weed (Alternanthera philoxeroides) is an aquatic or semi-aquatic perennial herb in the family Amaranthaceae, notorious as one of the world's worst aquatic invasive weeds — yet its young shoots and leaves are edible and are in fact eaten as a vegetable in parts of South America, its native range. This paradoxical plant chokes waterways across five continents while simultaneously being a traditional food in its homeland.
• One of the world's most aggressive aquatic invasive plants, choking rivers, canals, and lakes on every continent
• Despite its invasive reputation, young shoots are eaten as a vegetable in South America
• Can grow as a fully aquatic plant, a semi-aquatic plant, or entirely on dry land
• Extremely difficult to eradicate — fragments as small as 2 cm can regenerate into new plants
• Related to the edible sessile joyweed (Alternanthera sessilis)
• Named for its habit of forming dense mats that look like alligator skin on the water surface
Taxonomía
• Native to southern Brazil, Paraguay, Uruguay, and northern Argentina
• Introduced to the United States in the 1890s, likely as a contaminant in ship ballast
• Now invasive in the southeastern United States, Australia, New Zealand, Southeast Asia, China, and India
• First described by the Austrian botanist August Grisebach in 1879
• In its native range, it is a harmless component of wetland ecosystems
• Outside its range, it costs millions annually in waterway management
• In Australia, it is classified as a Weed of National Significance
• Biological control using the alligator weed flea beetle (Agasicles hygrophila) has been partially successful
• In parts of Southeast Asia, local communities harvest and eat it despite its invasive status
Stems:
• Hollow, buoyant (in aquatic form), allowing the plant to float
• Green to yellowish-green, smooth, 50 to 100+ cm long
• Root at the nodes
• Terrestrial forms have solid stems; aquatic forms have hollow stems
Leaves:
• Lanceolate to oblanceolate, 3 to 10 cm long and 1 to 2 cm wide
• Dark green, glossy, smooth, slightly fleshy
• Opposite arrangement
• Sessile or short-petiolate
• Entire margins, with a prominent midrib
Flowers:
• Small, white, 1 to 1.5 cm in diameter
• Born in dense, clover-like, ovoid heads 1 to 2 cm in diameter
• On long stalks (peduncles) 3 to 8 cm
• Five white, papery tepals
• Blooms in summer
Fruit:
• Seed production is extremely rare outside the native range
• Reproduction is primarily vegetative through stem fragmentation
• In the native range, small utricles containing seeds may be produced
• Per 100 g fresh shoots: approximately 25 to 35 kcal
• Contains vitamins A and C
• Provides iron, calcium, and potassium
• Moderate protein content for a leaf vegetable
• Contains dietary fiber
• Similar nutritional profile to related Alternanthera species
• Typically consumed in small quantities as a supplementary vegetable
• WARNING: It is ILLEGAL to cultivate or sell alligator weed in many countries
• In Australia, New Zealand, and parts of the USA, strict regulations prohibit its cultivation
• For foraging only: harvest young shoots from established invasive populations in areas where collection is permitted
• Collect only young, tender shoots and leaves
• WARNING: Never transport plant fragments — even tiny pieces can start new infestations
• Do not dispose of any plant material in waterways
• In its native South America, it is cultivated as a vegetable without ecological concerns
• If found outside its native range, report to local invasive species authorities
• Biological control agents (flea beetles) are used in some regions for management
• In its native South America, young shoots and leaves are cooked as a potherb
• Used in soups, stews, and stir-fries
• Can be prepared similarly to spinach or water spinach
• The flavor is mild and slightly grassy
• In parts of Southeast Asia, foraged from waterways and cooked as a vegetable
• Always cook thoroughly before eating
• Combined with other vegetables in mixed dishes
• Used as a famine food in some regions
• Not commonly sold in markets due to its invasive status in most countries
• In Myanmar and Thailand, sometimes added to curries
Dato curioso
Alligator weed is so aggressive that a single plant fragment the size of your fingernail can start an infestation that covers an entire lake within a single growing season
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