Alligatorweed (Alternanthera philoxeroides)
Kingdom: Plantae, Division: Tracheophyta, Class: Magnoliopsida, Order: Caryophyllales, Family: Amaranthaceae, Genus: Alternanthera, Species: A. philoxeroides · Amaranthaceae (Amaranth family) · Simple, perennial or annual depending on climate
Species
Alternanthera philoxeroides
Leaf Type
Simple, perennial or annual depending on climate
Family
Amaranthaceae (Amaranth family)
Shape
Oblanceolate to elliptical
Size
Approximately 1 to 3 inches long and 0.5 to 1 inch wide, typical for the species
Margin
Entire (smooth)
Arrangement
Opposite
Rarity
Very Common in its introduced and invasive ranges
Color & Pattern
Medium to bright green upper surface with a paler green underside, uniform coloration without distinct variegation
Venation Pattern
Pinnate with a prominent central midrib
Texture & Surface
Slightly puberescent to glabrous, somewhat matte finish
Description
Alternanthera philoxeroides, commonly known as alligatorweed, is a robust herbaceous plant capable of growing in both aquatic and terrestrial environments. It forms dense mats of hollow-stemmed vegetation with opposite, simple leaves and produces small, white, clover-like flower heads.
Key Features
Hollow stems, opposite leaves with entire margins, distinct white pom-pom-like flowers, and the ability to thrive in both wet and dry soils
Habitat
Aquatic to semi-aquatic habitats including marshes, ponds, drainage ditches, and moist terrestrial soils
Geographic Range
Native to South America (Parana River region), widely naturalized and invasive across southeastern North America, parts of Asia, Australia, and New Zealand
Condition Notes
Good health, showing typical green pigmentation with minor insect grazing marks common to wild specimens
Interesting Facts
Alligatorweed is a highly aggressive aquatic weed capable of choking out waterways, blocking navigation, and outcompeting native vegetation. It reproduces primarily through stem fragments rather than viable seeds in many introduced regions.
Medicinal & Uses
Generally regarded as a problematic invasive weed rather than having widespread modern uses, though historically used in traditional practices in its native range. No major commercial value.
Ecological Role
Acts as an aggressive invasive species that disrupts aquatic ecosystems, reduces dissolved oxygen in water bodies, and crowds out native flora
Similar Species
Other Alternanthera species such as Alternanthera sessilis (sessile joyweed), which typically lacks the hollow floating stems and has sessile flowers directly in the leaf axils
Foraging Tips
Look for dense mats along ditch banks, ponds, and slow-moving streams, particularly in warm temperate to subtropical climates
Toxicity Warning
Non-toxic to humans, but can accumulate heavy metals or nitrates if growing in polluted waters, making foraging from unknown water sources risky