Fern Friday: Giant-ness

Giant leather fern (Acrostichum danaeifolium) is the largest fern in North America. Its fronds can grow to be 15′ tall. When we visited Osprey Aces Stormwater Park and Nature Preserve, we saw giant leather fern growing in the rocks on the edge of one of the wetland stormwater cleansing ponds.

The rock rip-rap appears has been colonized by giant leather fern, far smaller shield fern (Thelypteris sp.), and some grasses. You will find giant leather fern growing in moist places, both fresh and brackish, throughout central and south Florida. Florida is the only state in which the tropical fern grows. Its range includes tropical central America, south America, Puerto Rico, and the Virgin Islands.

Ferns are very primitive plants from the days of dinosaurs and reproduce by tiny wind-borne spores. Fertile fronds, fronds that have reproductive spores, of giant leather fern are taller than “regular”, non-fertile fronds, as you can see in the photo below taken at Pelican Island National Wildlife Refuge …

The underside of the leaflets of fertile fronds are covered with golden brown or reddish spore cases (sporangia) that resemble suede. This characteristic is distinctive: Only a very few genera of ferns have spore cases that completely cover the underside of their leaflets.

Older giant leather fern can be identified by their sheer size. They can grow to be 15’ tall and more than 6’ wide. Non-fertile fronds have coarse, leathery leaflets that are dark green above and paler green below. One of its ascending or arching fronds can have 20 to 60 individual leaflets. Like all ferns, the fronds of giant leather ferns begin as fiddleheads, coiled up fresh fronds.

The roots of giant leather fern are strong, spongy and rhizomatous. Their structure helps to stabilize shorelines.

You can include giant leather fern in your landscape wherever it will have “wet feet”, be it sunny or shady. Just be prepared for its ultimate giant size.