February Ferns: Giant Leather Fern

Giant leather fern (Acrostichum danaeifolioum) lives up to its common name. This fern is pictured above at one of the reflection ponds at Bok Tower.

Known as the largest fern in north America, its fronds can reach up to 12′, and it can grow to be 5 – 10′ wide. This clumping fern of moist places is very versatile: It will grow in sun or substantial shade and in fresh or brackish water.

Below it is pictured growing at Cypress Bend Community Preserve in fresh water along the St. Sebastian River along with false indigo (Amorpha fruiticosa).

This enormous fern grows in moist areas throughout the Oslo Riverfront Conservation Area (ORCA) and is prevalent along the coastal wetland crossover bridges where Diane LaRue (Class of 2012) provides scale …

Its leaflets (pinnae) are lanceolate with pointed tips (acute apices). The edges (margins) of the leaflets are entire.

Below you can see a fertile frond growing on a mosquito control dikes at the Florida Medical Entomology Laboratory underneath a strangler fig (Ficus aureum).

Fertile fronds are more erect than “regular” fronds. All of the leaflets are covered with golden brownish spore cases (sporangia). This character differentiates giant leather fern from golden leather fern (Acrostichum aureum), a threatened species that ranges as far north as Martin County on the east coast. Golden leather fern only has sporangia on its uppermost leaflets, does not grow to be as large, and has more space between the individual leaflets (pinnae).

These ferns belong to the family Pteridaceae. The genus Acrostichum is derived from the Greek words akros (terminal) and stichos (a row). The species name of giant leather fern, danaeifolium, also is of Greek origin means having leaves like Danae (named for the mythological Greek daughter of the King of Argon). Aureum, the species name for golden leather fern and strangler fig (also know as golden fig), means golden in Greek.

Common plant names can be confusing, and folks sometimes call Acrostichum danaeifolium by the name golden leather fern, which should be “reserved” for Acrostichum aureum. Other common names for giant leather fern include mangrove fern and swamp fern. In the right light and at the right time of development, the sporangia on fertile leaves appear golden.

The central stem (rachis) also has a golden hue …

The fronds of of all ferns begin as a fiddlehead (crosier), all coiled up …

Usually the central “stem” (rachis) is straight but will sometimes be bent when it has encountered an impediment as it unfurled …

Giant leather fern could be a wonderful addition to your landscape in a moist place, sunny or shady. Look for this substantially sized fern throughout our County including at Pelican Island National Wildlife Refuge, where it is shown going with salt meadow cordgrass (Spartina patens).

Look for landscape lessons in Nature!

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