Pterophyta Filicales |
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| Some Ferns are Pioneer organisms on Lava Flows like these from Hawaii Volcanoes National Park. | ||
This is a large and familiar taxon. We are only studying the Filicales. However, there are several other classes that we are not considering.
The Filicales is the largest and most wide-spread taxon of ferns, and thus the best representatives this Division. They occupy a wide range of habitats. They are commonly terrestrial or epiphytic in the Tropics. Terrestrial forms predominate in the Temperate zone.
 Sadleria sp. This is a tree fern from Haleakala National Park, Maui |
 New Sadleria Fronds display Circinate Vernation |
 Sadleria Habitat |
 Cibotium sp. Tree Fern from Volcanoes National Park, Hawaii |
 Cibotium Fronds are Pinnately Compound Megaphylls |
 Cibotium Fronds seen from above. |
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| The aquatic fern Azolla is one of the smallest ferns. | Staghorn Fern: A Most Famous Epiphyte | "Filmy Fern" Manoa Cliffs Trail (Oahu) |
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| Habitat Overview of the smallest Hawaiian fern Gonocormus minutus (Minute Fern that comes from a Bulb). It is one example of a "Filmy Fern". | Gonocormus minutus grows in wet places among Moss and Liverworts. Due to its size it is hard to distinguish it from its neighbors. | Gonocormus minutus has Dichotomously organized Megaphylls. The Sporangia are found in cup-like leaf outgrowths. |
The
Filicales contains many large families including the Polypodiaceae,
Osmundaceae,
& Cyatheaceae plus several others. There are approximately 300 genera & 9,000
species. These are most abundant in the
humid tropics but they are also plentiful in temperate regions,
including temperate rainforests like those found on the Olympic peninsula
(Washington) and New Zealand. A few species are aquatic or
semi-aquatic while a few species can survive in arduous environments.
Ferns are relatively small
plants and they do not generally 
dominate ecosystems, However, they can be
very important in certain environments. Tree ferns may be among the dominant species
is certain places. This is true for the Hawaiian Islands. Ferns have
greater ecological significance in Hawaii than elsewhere due to the absence
of competitors which would normally displace them as sites mature. In
some cases ferns are the only significant ground cover in Hawaiian forests and open slopes.
They are consequently important for soil stabilization and erosion
control. They should be considered for the initial revegetation
of some disturbed sites.
The
class that we are studying is characterized by pinnate leaf
organization.
This is evident in their venation (vein
pattern) and the overall appearance of their lamina
(blade). However, there are ferns
which have entire, lanceolate leaves. Some have Palmate
organization while others are Dichotomous..
Another
diagnostic leaf characteristic is Circinate
Vernation. Immature leaves are tightly coiled and tightly packed at
the shoot apex. The leaves begin to uncoil when favorable
conditions occur. They resemble the tops of violins
and have been called "fiddle
heads". They also resemble the shepherd's
crook and have been so named. The fiddle heads mature from the
base towards the tip (acropetal maturation). Consequently, the
lower sections of the petiole and blade mature first. The leaflets
of compound leaves also display circinate vernation. 
Ferns have Megaphylls (large leaves). However, size is not the chief characteristic of megaphylls. A Megaphyll is a leaf which contains more than one vein and its leaf trace is associated with a leaf gap in the stele. A leaf gap occurs when the departure of a leaf trace from the stele results in the development of parenchyma rather than vascular tissues in the stele, just above the leaf trace. This gives the stele a dissected appearance like the dictyostele.
Some
ferns have very simple leaf
organization with little mesophyll
differentiation. 
Others have a complex anatomy which rivals the structural specialization of angiosperm leaves.
