Excerpts from Jim Conrad's
Naturalist Newsletter

from the May 8, 2016 Newsletter with notes from a visit in mid April to Lacanja Chansayab in the Lacandon Reserve, Chiapas, MÉXICO
CLIMBING FERN
On April 14th as I hiked small gravel backroads around Lacanja Chansayab in Chiapas's Lacandon Reserve, along the road I came upon a vine with extraordinary compound leaves twining across a dense wall of tree and shrub branches, shown below:

LYGODIUM VENUSTUM

In Mississippi we've something like this. You can confirm how similar the "leaves" are at http://www.backyardnature.net/n/x/climfern.htm

The Mississippi plant was the invasive Japanese Climbing Fern, Lygodium japonicum, a real fern, with extraordinary anatomy. Our Chiapas fern is the closely related LYGODIUM VENUSTUM, native from central Mexico and the Caribbean south through Central America and most of tropical South America. Species of Lygodium often are known as climbing ferns.

What's amazing about climbing fern anatomy is that what appears to be the fern's wiry stem stretched across my fingers in the picture is actually the frond's midrib, or rachis. The two "fronds" in the picture and several others along the wiry stem, are subdivisions of one extremely long frond. In the technical words of my old Bailey's Manual of Cultivated Plants, in the genus Lygodium "... the 'lvs.' are secondary pinnae, which are palmately or pinnately compound or decompound."

On the margins of the leaflets, or secondary pinnae, notice the tiny, dark green, fingerlike items, of which a close-up of several is seen below:

LYGODIUM VENUSTUM, marginal spikes

Ferns reproduce with spores, and these structures, sometimes called marginal spikes, are where the spores are produced. You might know that fern spores are produced inside microscopic, baglike-items known as sporangia, and in many kinds of ferns the fronds' groups of sporangia are partly or completely covered with a thin layer of tissue called the indusium. This climbing fern's marginal spikes are composed of overlapping indusia. In the picture, each green, scale-like item is an indusium that if you should peel one back you'd find sporangia inside which spores are developing.

In Mexico Lygodium venustum sometimes is known as Hierba de la Víbora, which can be loosely translated as Snake Plant. It's famed as treatment for snakebite and scorpion stings. After being bitten, the fronds can be eaten directly. Also, teas can be made of the whole plant for diarrhea, dysentery, and for various female diseases.