Excerpts from Jim Conrad's
from the February 1, 2015 Newsletter issued from Río Lagartos, on the north-central coast of Yucatán, MÉXICO
GIANT SWORD FERN
About a kilometer into the mangroves east of Río Lagartos, at Petén Tucha where we've seen Spider Monkeys swinging among branches of strangler fig trees, some years ago a tree fell, opening the canopy so that sunlight, at least at mid-day, floods onto the forest floor. The forest floor there is ankle-deep in brackish water. Nature's reaction to this penetration of sunlight into an otherwise shadowy and somber understory has been to engender the massive tangle of eight-ft-tall (2.5m) ferns, shown at the top of this page.
Those giant ferns glowing in sunlight during their brief mid-day photosynthetic rush put one in mind of the Carboniferous Period 300 million years ago, when giant dragonflies glided among treelike lycopods, seed ferns, horsetails and cordaites, whose dead bodies when sunk into swamp mire eventually lithified into the stuff we call coal. But the sunlight does something else, too: They backlight certain fronds so that their clusters of fruiting bodies, or sori, easily can be seen on pinna undersides, as shown below:
Seeing the sori is important because every fern has its own way of grouping its spore producing sporangia, so if you can see the sori, you've seen important field marks. In the last photo this big fern's sori look like round warts in single file just inside the pinnae's margins. Another good field mark is the fern's stiff main stem, or rachis, that almost looks woody, and is round in cross section.
This is the Giant Sword Fern, NEPHROLEPIS BISERRATA, occurring throughout the Earth's tropical and semitropical regions in a variety of habitats, not only in mangroves and woody swamps but also sometimes in clearings and roadsides, and even epiphytically on trees. In the US they occur in southern Florida.
At Petén Tucha the Giant Sword Fern is so rank and robust that you can't imagine taming it in a pot on your patio, but that's exactly what many gardeners do. Then the fern at best gets only half the size we see here, but it makes a handsome landscaping plant, and even looks good in baskets hung so that the fronds cascade over the size.