Fern

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Classification/Diagnostic Characteristics


Ferns are categorized under the clade monilophytes, also known as "fern and fern allies". Within that clade, there are more than 12000 species that can be classified as leptosporangiate ferns, the largest of four subdivisions of ferns. The majority of ferns are terrestrial and can be identified by their large leaves and branching vascular strands. Certain species of ferns can climb surrounding structures and grow up to 30 meters in length. The sporophytes of ferns are large and can survive for centuries, while the gametophytes in alternating generations of ferns are small, delicate, and short-lived. A fern's sporangia, vessels where reproductive spores are most commonly found in clusters called located sori, which are often located on the underside of leaves. (1)

Ferns contain true roots, stems, and leaves. Fern leaves, also known as fronds, are considered to be megaphylls, which means that they possess several vascular strands that conduct water and nutrients throughout the plant body. When the fern leaves first emerge they are tightly coiled and called fiddleheads for their resemblance to the top portion of the fiddle instrument. The leaves arise from an underground stem known as a rhizome, which serves as the attachment point for the underground roots.The phylogeny of modern ferns is as follows:

Domain - Eukarya
Kingdom - Plantae
Division - Pteridophyta
Class - Pteridopsida
Order - Athyriales


Further classification of ferns is based on whether or not they are protected by a covering called an indusium, the shape of the fronds, and how the fronds unfold. (Alexander Soloviev)

http://www.sas.upenn.edu/~joyellen/fernreproduction.html

Relationship to Humans


Ferns are popular horticultural plants, as many of them are grown in ornamental or indoor gardens. Additionally, the fossils of these plants, because they were once the dominant terrestrial plants, contribute greatly to coal, oil, and natural gas. Some non-western cultures also use ferns for food or for treating ulcers, rheumatism, and other infections.
http://science.jrank.org/pages/2689/Ferns-Importance-humans.html (BHu).

Besides ornamental purposes, ferns are also used as stuffing material (ex. in bedding, etc.) in tropical areas. The ferns fronds can be used as material when weaving baskets, hats, etc. and also is used when brewing certain types of ales. (http://www.biology-online.org/11/13_vascular_plants.htm) Medically speaking, in India, fern extract, rhizome, mixed with water, seems to be used for various neurological illnesses, like epilepsy, as well as headaches. (http://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1029&context=ebl)

Habitat and Niche


Most ferns can be found in shaded, moist environments such as woodlands and swamps. (1)

These environments can be either temperate or tropical, although they must be warmer and wetter. The fern is versatile in that it grows equally successfully on any most surface, whether it be rocks or soil. It typically grows in the early stages or forest succession due to it growing easily in a variety of locations. (Colin Gray)
http://www.britannica.com/EBchecked/topic/204819/fern#toc49908

The biggest variety of ferns can be found in places with plenty of moisture and shade. Ferns can turn the forest floor into a carpet, while others give the under story thousands of shades of green. In the woodlands, the variety of ferns is less.
http://www.vumba-nature.com/about_ferns.htm#Habitats

Ferns are most abundant in damp, New Zealand forests beneath evergreen trees and on trees along stream banks. They require damp, humid envrionments so they are in danger where forest conditions changes.
http://www.doc.govt.nz/conservation/native-plants/ferns/

Predator Avoidance


Like other plants, some ferns are capable of producing toxic substances to fend of herbivores. Unlike some plants, like flowering plants, ferns do not need to attract pollinators, decreasing the chance for herbivores to find them. (http://phys.org/news/2012-11-herbivore-defence-ferns.html)

Predators of ferns include the European woodmouse and the Azores Bullfinch
http://news.bbc.co.uk/earth/hi/earth_news/newsid_8523000/8523825.stm

Nutrient Acquisition

Ferns contain a vascular system that uptakes water and minerals from the roots of the plant. The xylum continues up to the stem and leaves and once the water reaches this point it evaporates and the water shoots up the fern from the roots. (Cam Somers) http://www.britannica.com/EBchecked/topic/204819/fern/49914/Ecology

The fern's vascular system is also composed of phloem, which distributes sugars around the plant and consist of live cells. In general, the xylem is found inside the vascular bundle in the stem, surrounded by phloem.
http://biology.clc.uc.edu/courses/bio106/mosses.htm

Reproduction and Life Cycle


Ferns undergo a sexual life cycle that is known as alternation of generations. This means that the plant goes through multicellular haploid and diploid stages of life. The cycle begins with meiosis, a process of cell division that produces daughter cells that contain half the genetic material of the original cell, and this ends up creating spores. The spores germinate after being disseminated from the parents plant and and develop small appendages called rhyzoids, which absorb nutrients and water from its surroundings in order to sustain the growth of the spore. When the spore's growth reaches about 0.5 centimeters wide, it becomes what is known as a mature gametophyte. The gametophyte represents the haploid stage of the fern's life cycle. Within the gametophyte, there are individual sections that house the eggs and sperm of the fern; the structure that houses the eggs are called archegoniums and the structure that houses the sperm are called antheridium. Since ferns develop a single type of spore that each contain the separate gametes of the parent plant, ferns can be categorized as homosporous plants. After a certain amount of time in the gametophyte's life, the archegoniums and antheridiums open up, and the sperm migrate to the archegoniums, where they fertilize the egg to create embryo. After fertilization, the organism becomes diploid because the genetic material doubles. The embryo allows for the development of a appendage called the sporophyte, which eventually grows into the broad, branching vascular leaves that characterize ferns. Mature sporophyte develop sori clusters on the underside of their leaves, groups of sporangium that house the spores of the next generation. The immature spores then undergo meiosis, and the cycle begins again. (1)

Fern_life_cycle2copy.jpeg
http://amerfernsoc.org/lernfrnl.html

Growth and Development:

Life cycle of a typical fern:
  1. A diploid sporophyte phase produces haploid spores by meiosis (a process of cell division which reduces the number of chromosomes by a half).
  2. A spore grows into a haploid gametophyte by mitosis (a process of cell division which maintains the number of chromosomes). The gametophyte typically consists of a photosynthetic prothallus.
  3. The gametophyte produces gametes (often both sperm and eggs on the same prothallus) by mitosis.
  4. A mobile, flagellate sperm fertilizes an egg that remains attached to the prothallus.
  5. The fertilized egg is now a diploid zygote and grows by mitosis into a diploid sporophyte (the typical "fern" plant).
http://en.wikipedia.org/wiki/Fern
fern.jpg
A fern is referred to as a 'fiddle head' in its early growth stages. The fern subsequently unrolls upwards, and then spread its leaves outward. Fun fact: fiddle heads are a fairly common food and are sometimes put on salads!


Integument


Acting as support and protection from uv rays, desiccation, and potentially dangerous chemicals, ferns are covered by a thin, non-cellular layer called the plant cuticle. (GC)
http://www.uni-muenster.de/GeoPalaeontologie/Palaeo/Palbot/cuticles.htm

Movement

While the fern, as with most Like other plants, cannot actually move on its own whim, it is a plant with chloroplasts. Meaning, under high-light levels, the chloroplast will line up parallel to the light across the cell wall, causing the plant to physically grow in the direction of light. In low-light levels, the chloroplasts grow perpendicularly to the light (Prashant). http://plantsinmotion.bio.indiana.edu/plantmotion/projects/livingpics/livingpics.html

Like other plants, ferns can not move. They spread, however, through spores, from which free-living bisexual gametophyte generations develop.
http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookdiversity_5.html#The Ferns



Sensing the Environment

Ferns as well as other plants in the world all sense the environment by growing towards their light source to obtain more sunlight for food and to live a sustained life. This process of a plants growth towards the sunlight is know as phototropism. Tropism is the growth of a plant in a response to a stimulus, and phototropism is the repose of a plant to light by bending in the direction of the light.

http://www.scienceclarified.com/Oi-Ph/Phototropism.html#b


Gas Exchange


Guard cells and the stomata play a central role in the gas exchange of the environment within ferns. The stomata normally opens when light strikes the leaf during daytime, and closes to preserve water during the night. When open, carbon dioxide flows freely through a permeable membrane in, and oxygen out through the process of photosynthesis. The stomata also opens and closes based upon the status of the guard cells. When filled with water and properly hydrated, it causes the guard cells to bulge out, forcing the stomata to open. When there is a dearth of water, the inner walls of the guard cells dry up and close, mainly to prevent water loss and gas exchange (Prashant).
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/GasExchange.html


Waste Removal

Ferns remove waste by transpiration. The fern has a stomata which gives off the unused water. Also, in photosynthesis, the ferns remove O2. (Evan Kates) (http://www.genomenewsnetwork.org/articles/2004/08/06/fern.php)

Environmental Physiology (Temperature, Water, and Salt Regulation)


Most ferns prefer tropical or subtropical regions, regions synonymous with high levels of sunlight, rainfall, and high humidity. Temperature-wise, the optimal growing conditions for ferns during the day time is around 72 degrees Fahrenheit, while the nighttime temperature should be around 60 degrees Fahrenheit. Because ferns themselves are such a varied species with many sub-species, there really is no "perfect" condition that adheres to all ferns. Speaking in general though, ferns need a constant supply of moisture, and particularly during their primary growing season, almost daily. (Prashant). http://www.caes.uga.edu/applications/publications/files/pdf/B%20737_3.PDF


Internal Circulation


Ferns are vascular plants, which means they have complex vascular systems containing tissues that are specifically used for the transport of materials across the internal parts of the plant. An example of an important vascular tissue is the xylem, which conducts water and minerals from the soil to all other parts of the plant that requires it. It is important to note that the branching sporophytes of ferns can develop and grow nutritionally independent of the gametophyte when they reach full maturity. (1)

Another example of a vital vascular tissue is the phloem, which transports essential nutrients, such as glucose and sucrose, throughout the the plant to the needed areas. It works in tandem with the xylem to maintain homeostasis and regulatory behavior within the fern.
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Chemical Control

Plant hormones, also known as phytohormones, do not directly contribute to bodily processes such as digestion and growth due to the fact that plants do not have formal circulatory systems, but they do play minor roles in modifying these biological mechanisms in response to environmental stimuli. This is very different from the endocrine system of animals, which have circulatory systems to transport hormones across their entire bodies efficiently; hormones play a smaller part in a plant's life than in an animal's life. The five main phytohormones are auxins, cytokinins, ethylene, abscisic acid, and gibberellins. These five phytohormones all perform different functions within a plant. (http://www.hcs.ohio-state.edu/hcs300/hormone.htm)

Review Questions

1. Describe how ferns differ from gymnosperms and angiosperms in reproduction.

2. Describe how cuticles and phloem and xyelm tissues are advantageous for ferns.

3. What is the structure of the adult fern within which cells undergoing meiosis can be found?

4. What are the main differences between the gametophytes and sporophytes of ferns?

5. Ferns were one of the first vascular plants. What are the main differences between ferns and the nonvascular plants that still exist today (moss, hornworts, liverworts)? Use the other wikipages to come up with an answer!

References


‚Äč1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.