Sword Fern (Nephrolepis)

The genus Nephrolepis, commonly known as the sword fern or Boston fern, is a staple of Florida’s landscape. Yet, within this single genus lies a dramatic contrast: a beloved native species providing critical habitat, and an aggressive, “tuberous” imposter that is systematically dismantling local ecosystems. Understanding the Sword Fern in Florida requires peeling back the layers of its biology, its history in the Victorian parlor, and the ongoing battle to protect Florida’s biodiversity from a plant that looks nearly identical to its native cousin.

The Native Soul: Nephrolepis exaltata and biserrata
Florida is home to two primary native species of sword fern: the Wild Boston Fern (Nephrolepis exaltata) and the Giant Sword Fern (Nephrolepis biserrata).

The Wild Boston Fern (N. exaltata)
This is the quintessential Florida fern. Found in swamps and wet hammocks from the Everglades up through the central peninsula, it is a resilient survivor. It grows both on the ground (terrestrial) and on other plants (epiphytic), often seen tucked into the “boots” of Cabbage Palms. Its fronds are elegant, lance-shaped, and can reach up to 5 feet in length.

The Giant Sword Fern (N. biserrata)
Living up to its name, this species is the “big brother” of the group. Its fronds can tower over a person, sometimes reaching lengths of 7 to 10 feet. It favors the deep, moist shade of cypress swamps and limestone sinkholes in South Florida.

These native ferns are vital to the Florida ecosystem. They provide cover for small reptiles, amphibians, and invertebrates. Their presence is a sign of a healthy, hydrated woodland, serving as a natural moisture regulator for the forest floor.

The Imposter: Nephrolepis cordifolia
The primary villain in Florida’s fern narrative is the Tuberous Sword Fern (Nephrolepis cordifolia), often called the Erect Sword Fern. Native to the global tropics outside of Florida, it was likely introduced as an ornamental plant in the early 20th century. By 1933, it was documented as an “escapee” in Sumter County; today, it is classified as a Category I invasive species by the Florida Invasive Species Council (FISC).

Why is it so dangerous?
Unlike the native species, N. cordifolia is an aggressive colonizer. It spreads through three distinct methods:

Spores: Wind-borne spores allow it to leapfrog into distant, pristine conservation areas.
Stolons: Above-ground runners allow it to crawl across the forest floor, choking out native groundcover.
Tubers: This is its “secret weapon.” N. cordifolia produces small, round, underground storage organs (tubers). These tubers store water and nutrients, allowing the plant to survive droughts or freezes that would kill native ferns. Even if a gardener pulls the plant up, if a single tuber remains in the soil, the fern will regrow.

In natural areas, this fern forms dense, impenetrable monocultures. It displaces not only the native N. exaltata but also rare wildflowers and seedling trees, effectively halting the natural regeneration of the forest.

The Identification Challenge: How to Tell Them Apart
Because they look so similar, many Florida homeowners unknowingly plant the invasive variety, thinking they are supporting local wildlife. Distinguishing them requires a keen eye for botanical detail.

The Horticulture Connection: The “Boston” Fern
The history of Nephrolepis is inextricably linked to the “Pteridomania” (fern fever) of the Victorian era. In 1894, a florist in Boston discovered a mutation in a shipment of N. exaltata from Florida. This mutant had wider, more gracefully drooping fronds than the wild type. It was dubbed the “Boston Fern” (Nephrolepis exaltata ‘Bostoniensis’).

This single plant sparked a global industry. Today, Florida remains a hub for fern production, but this commercial success is a double-edged sword. Because “Boston Fern” is used as a catch-all marketing term, big-box retailers often sell the invasive N. cordifolia or the non-native N. brownii (Asian Sword Fern) under the same name. This leads to “accidental” invasions when homeowners toss old hanging baskets into the woods behind their houses.

Management and Control in the Florida Landscape
Controlling sword ferns in Florida is a labor-intensive process. Because of the aforementioned tubers, simply “weeding” the plants is rarely effective.

Physical Removal
To successfully remove invasive sword ferns, you must dig up the entire root mass. Every tuber must be bagged and disposed of in the household trash—never in a compost pile or “green waste” bin, as the tubers can survive the composting process and spread to new locations.

Chemical Control
For large-scale infestations in natural areas, land managers often use herbicides. A $1.5\%$ to $2\%$ solution of glyphosate is generally effective. However, because these ferns often grow on or near native trees (like palms), great care must be taken to avoid “non-target” damage. Often, a follow-up treatment is required six months later to kill the “regrowth” from dormant tubers.

The Path Forward: Planting Native
The best way to support the “real” Florida sword fern is through conscious gardening. By choosing verified native N. exaltata or N. biserrata from reputable native nurseries, residents can provide essential habitat for Florida’s fauna without the risk of an invasive takeover.

The story of the Sword Fern in Florida is a reminder of the delicate balance of our subtropical ecosystem. In a state where the line between “lush paradise” and “invasive jungle” is paper-thin, the difference between a native treasure and an ecological threat often comes down to a tiny, brown tuber hidden beneath the soil.

Conservation Tip: If you are unsure which fern you have, look for the “bulbs” in the roots. If you see them, you have the invader. If the roots are just a mass of fine, fuzzy hair, you likely have a native friend.