Old World Climbing Fern

Lygodium microphyllum is native across a broad swath of the Old World tropics and subtropics, including:
• Sub-Saharan Africa
• South and Southeast Asia (India, Sri Lanka, southern China, Indochina, Malaysia, Indonesia)
• Northern and eastern Australia
• Various Pacific islands

It was introduced to southern Florida, USA, likely in the late 19th or early 20th century as an ornamental plant. It was first documented as naturalized in Florida in 1965 and has since spread aggressively throughout the state.

The genus Lygodium comprises approximately 40 species worldwide, with the greatest diversity in tropical Asia. Fossil evidence suggests the lineage is ancient, with related forms dating back to the Cretaceous period.

Lygodium microphyllum is morphologically distinctive among ferns due to its climbing habit.

Rhizome & Stipes:
• Rhizome is creeping, slender, and wiry, branching extensively underground
• Covered with dark brown to blackish hairs
• Stipes (leaf stalks) are slender, tough, and flexible, enabling twining around supports

Fronds:
• Fronds are indeterminate in growth — the rachis (central axis) continues to elongate indefinitely, climbing over other vegetation
• Fronds can reach lengths of 30 meters (nearly 100 feet) in optimal conditions
• Pinnae (primary leaflets) are arranged alternately along the rachis
• Each pinna bears 5–12 pairs of pinnules (ultimate leaf segments)
• Pinnules are small (~1–3 cm long), narrowly lanceolate to oblong, with entire or shallowly lobed margins
• Texture is herbaceous to slightly leathery; color bright green to dark green
• Sterile and fertile pinnules are dimorphic — fertile pinnules are smaller and bear sporangia along their margins

Sori & Spores:
• Sori are borne on the margins of fertile pinnules, protected by reflexed leaf margins forming false indusia
• Spores are trilete (tetrahedral), pale brown, and minute (~40–50 micrometers)
• A single frond can produce millions of spores, facilitating rapid colonization of new areas

In its native range, Lygodium microphyllum occupies a variety of moist habitats:
• Edges of tropical and subtropical forests
• Riparian zones and swamp margins
• Disturbed areas and secondary growth
• Elevations from sea level to approximately 1,500 meters

In its invasive range (notably Florida), it thrives in:
• Cypress swamps and wet prairies
• Pine flatwoods and hardwood hammocks
• Canopy gaps and edges of tree islands
• It climbs over shrubs and trees, forming dense mats that can reach the upper canopy

Ecological Impact (Invasive Range):
• Smothers native vegetation by blocking sunlight, leading to die-off of understory and canopy plants
• Dramatically increases fire risk — the climbing fronds act as "fire ladders," carrying ground fires into the tree canopy where they kill mature trees
• Alters hydrology and nutrient cycling in wetland ecosystems
• Reduces biodiversity by displacing native plant communities and the wildlife that depends on them

Reproduction:
• Spores are wind-dispersed over long distances
• Spores germinate into small, heart-shaped prothalli in moist conditions
• Also spreads vegetatively through rhizome fragments, which can be transported by water, animals, or human activity
• Rapid growth rate — fronds can elongate several centimeters per day under favorable conditions

Lygodium microphyllum presents a paradox in conservation biology:

In its native range:
• Not considered threatened; widespread and common across tropical Africa, Asia, and Australia
• No specific conservation measures are generally required

In its invasive range (Florida, USA):
• Listed as a Federal Noxious Weed under the United States Department of Agriculture (USDA)
• Classified as one of the most serious invasive species in Florida
• Active management programs include:
• Mechanical removal (labor-intensive and often ineffective due to rhizome regrowth)
• Herbicide application (triclopyr-based herbicides are commonly used)
• Biological control – the Australian moth Austromusotima camptozonale and the mite Floracarus perrepae have been studied and released as biocontrol agents
• Prescribed burning (though the fern's fire-ladder effect complicates this approach)
• The Florida Fish and Wildlife Conservation Commission (FWC) and the South Florida Water Management District coordinate ongoing eradication and containment efforts

Lygodium microphyllum is NOT recommended for cultivation outside its native range due to its highly invasive nature. In many jurisdictions, it is illegal to possess, sell, or transport this species.

In its native range, where it may be grown ornamentally:

Light:
• Prefers partial shade to full sun
• Tolerates a wide light range but grows most vigorously with some direct sunlight

Soil:
• Moist, well-drained soils rich in organic matter
• Tolerant of a range of soil types including sandy, loamy, and clay soils
• Prefers slightly acidic to neutral pH

Watering:
• Requires consistently moist soil
• Does not tolerate prolonged drought
• Thrives in humid, wetland-adjacent environments

Temperature:
• Hardy in USDA zones 9–11
• Cannot tolerate frost; damaged or killed by freezing temperatures
• Optimal growth at 20–30°C

Propagation:
• Spore sowing on moist, sterile medium
• Division of rhizome fragments
• Extremely vigorous once established — containment is essential