Ferns are a group of about 10,560 known extant species of vascular plants that reproduce via spores and have neither seeds nor flowers.
They differ from mosses by being vascular, i.e., having certain tissue that conducts water and nutrients. They have branched stems and leaves like other vascular plants.
These are "megaphylls", which are more complex than the simple "microphylls" of clubmosses.
Most ferns are Leptosporangiate ferns, sometimes denominated the "true ferns": they produce what are called "fiddleheads" that uncoil and expand into fronds.
Ferns first appear in the fossil record 360 million years ago in the late Devonian period but many of the current families and species did not appear until roughly 145 million years ago in the early Cretaceous, after flowering plants came to dominate many environments.
Some ferns have not changed for well over 100 million years
The fern Osmunda claytoniana is a paramount example of evolutionary stasis. Paleontological evidence indicates it has remained unchanged, even at the level of fossilized nuclei and chromosomes, for at least 180 million years.
Description or shapes aka morphology of ferns
- Fern stems are often referred to as "rhizomes", even though they grow underground only in some of the species. Epiphytic species and many of the terrestrial ones have above-ground creeping stolons (e.g., Polypodiaceae), and many groups have above-ground erect semi-woody trunks (e.g., Cyatheaceae). These can reach up to 20 metres (66 ft) tall in a few species (e.g., Cyathea brownii on Norfolk Island and Cyathea medullaris in New Zealand).
- The green, photosynthetic part of the plant is technically a megaphyll and in ferns, it is often referred to as a frond. New leaves typically expand by the unrolling of a tight spiral called a "crozier" or "fiddlehead fern". This uncurling of the leaf is termed "circinate vernation”.
Fern Leaves are divided into two types a trophophyll and a sporophyll.
- A trophophyll frond is a vegetative leaf analogous to the typical green leaves of seed plants that does not produce spores, instead only producing sugars by photosynthesis.
- A sporophyll frond is a fertile leaf that produces spores borne in sporangia that are usually clustered to form sori. In most ferns, fertile leaves are morphologically very similar to the sterile ones, and they photosynthesize in the same way.
- In some groups, the fertile leaves are much narrower than the sterile leaves, and may even have no green tissue at all (e.g., Blechnaceae, Lomariopsidaceae).
Simple or highly divided
The anatomy of fern leaves can either be simple or highly divided. In tree ferns, the main stalk that connects the leaf to the stem (known as the stipe), often have multiple leafy. The leafy structures that grow from the stipe are known as "pinnae" and are often again divided into smaller pinnules.
These are underground non-photosynthetic structures that take up water and nutrients from soil. They are always fibrous and structurally are very similar to the roots of seed plants.
source adapted from: Fern. (2017, February 3). In Wikipedia, The Free Encyclopedia. Retrieved 21:30, February 3, 2017, from https://en.wikipedia.org/w/index.php?title=Fern&oldid=763451846