Sometimes it can be hard to differentiate our native sword ferns – Nephrolepis exaltata & Nephrolepis biserrata from their invasive, non-native relatives – Nephrolepis cordifolia & Nephrolepis brownnii. All of these ferns, too often, are called Boston fern or, to add to our confusion, sword fern.
The “real” and original Boston fern in commerce since the 1890’s is Nephrolepis exaltata, called sword fern or wild Boston fern by the Florida Plant Atlas. We saw it growing in the wild when we visited the Coastal Oaks Preserve on 2-26-2022.
The fronds of sword fern grow to be 3 – 6′ long and have a graceful weeping habit. It always is a joy to see them.
Most often tuberous sword fern (Nephrolepis cordifolia) is what we see planted in yards, often overtaking other vegetation. Some nurseries continue to grow this invasive non-native fern, even though in 1999 the Florida Nurserymen & Growers Association agreed to phase out production of this fern. This all-too common fern has escaped into our natural areas. Neither of our native sword ferns have tubers. Most, but not all, tuberous sword ferns have round tubers that confirm ID. This fern tends to have shorter fronds and a more upright habit (as opposed to a weeping form), and its pinnae often overlap and have blunt rather than pointed tips …
Native sword words fern have round or horseshoe-shaped indusium (a flap of tissue that protects spores, shown below. Non-native sword ferns have kidney or crescent shaped indusium.
With their long weeping fronds, native sword ferns can be an excellent, but somewhat aggressive, landscape plant.