Ferns





Diagnostic Characteristics
//The Pterophyta are extremly diverse, so it difficult to state diagnostic characteristics for the entire group, but in general, the Pterophyta are seedless plants that have the advent of a vascular system with familiar roots, stems and leaves. (JS) [|6] //

There are three different categories of plants that fall under the phylum //Pterophyta//.
 * Psilophytes, also known as whisk ferns, have a dichotomous (Y-like) branching and possess neither true leaves nor true roots.
 * Ferns have no upright stems, but instead they have huge leaves (growing from a horizontal rhizome) with clusters of sporangia on leaf undersides. Each leaf is divided into several leaflets.
 * Sphenophytes or Horsetails have a brushy appearance and, unlike ferns, have upright stems. These stems are green and jointed and have small rings of leaves or branches attached to each joint.

**Major Types**

__Psilophytes__ are similar to ancient vascular plants, and they do not possess true leaves or true roots. Therefore, prior to DNA and ultrastructural analysis that show their close relatedness to ferns, they were places in their own phylum. This DNA and ultrastructural analysis shows that the lack of true roots and true leaves evolved when psilophytes diverged from ferns, and not prior to this divergence.

__Ferns__ are the most widespread and diverse members of the phylum Pterophyta; there are over 12,000 species of ferns. They grew during the Carboniferous period in the huge swamp forests, but today they can be found in the tropics, temperate forests, and arid climates.

__Sphenophytes or Horsetails__, similar to Psilophytes, were previously part of a separate phylum from ferns, but based on molecular data are shown to be close relatives of ferns. During the Carboniferous period, horsetails were huge and they varied considerably, but today there are only around fifteen species of horsetails.



**Habitats**

//Psilophytes are located in areas of warm weather, generally in the tropics and subtropics: they can be found in nations surrounding the Pacific ocean such as Japan, Australia, and New Zealand along with areas in the Gulf of Mexico like the Caribbean. In the U.S., they are generally found in swamp lands and on dry cliffs, but they also form large clusters near trees and flowerbeds. Psilophytes have no leaves, and it has a root-like stem called the rhizome, which anchors it to the ground (SD) (3).//

The greatest variety of ferns can be found at tropical latitudes. However, many ferns also grow in temperate forests, and a select few are present in arid climates. //The fern species of largest physical size occur in the tropics, where a considerable number occur in tree form. In Papua New guinea, it has been estimated that over one eighth of the world's fern species can be found. Some ferns are found even in extreme latitudes; in particular, the species Cryopteris fragilis occurs well up into the Arctic region. As a generalization, ferns occur more commonly and with greater diversity of taxa in the tropics and subtropics, regions in which many of the species are epiphytes. In some regions of the world certain fern species can gain dominance in a given habitat, often with undesirable outcomes. For example, in Great Britain and in New Zealand, ferns with the common name bracken can suffocate and crowd out entire plant associations, although the true species in these two cases are different. In many tropical lakes the Mosquito fern can take over large areas. (MP)// //[|8]// //Some ferns are adapted to a dry habitat but most prefer the shady moist conditions of woodlands. They are particularly abundant in tropical rainforests and in the modern world there are still thousands of different species of this ancient and very successful group. (CC) [|7] //

Horsetails are generally found in swampy marshes or next to streams. As a result, they are specially adapted to their soil, which is oxygen-poor because of the high water concentration.

**Basic Anatomy**

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Psilophytes (for example, the whisk fern) have stems that are branched in the shape of a “Y”, but they possess neither true leaves nor true roots. //It is a rootless, green stemmed epiphyte that is anatomically characterized as having a rhizome, which anchors the plant and absorbs nutrients, a spore producing organ called the synangium, and an angular stem axis. The stem is covered in stomates to allow gas exchange to occur, and the stem can also perform photosynthesis (SD) (4). The development of seeds arose from the retention of the embryo inside maternal tissue. Early seed ferns gave rise to the gymnosperm group, including pines, spruces, and firs. (MS)// [|4]

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Ferns have stems, but they are present above the ground. Rather, they possess rhizomes, horizontally oriented stems (found underground) from which large leaves (known as fronds) with extensively branched vascular systems grow. These leaves are divided into several smaller leaflets. As the fiddlehead (coiled leaf tip) of each leaf opens up, the fern frond grows. Also unlike many plants with which people are familiar, ferns do not produce seeds. Instead, ferns produce clusters of sporangia (capsules in which haploid spores develop) known as sori. These sori are stored on the undersides of special leaves and can be found in a variety of different patterns. Fern sporangia possess unique spring-like devices that aid in reproduction; these devices eject the sporangia from the leaves and allow them to become airborne, when they can be transported far away by the wind.



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Sphenophytes (aka horsetails) possess both traditional, upright green stems and rhizomes. The upright green stems (the major photosynthetic organisms of sphenophytes) are jointed, and a ring of small leaves or branches emerges from each joint. Additionally, these upright green stems contain large air canals within that permit the flow of oxygen gas into the roots and the rhizomes. At the tips of certain horsetail stems can be found cones that are composed of sporangia-producing leaves.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 17px; line-height: 25px;">**Transport of Materials**

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Ferns are some of the simplest and earliest vascular plants, plants that possess vascular tissue. The extensively branched vascular tissue found in ferns is crucial to the transport of water and nutrients. Xylem is the first type of vascular tissue, and it transports water and dissolved minerals from the roots of the fern to the leaves. Phloem is the second type of vascular tissue, and it transports food made in the leaves (via photosynthesis) to the roots and to other parts of the fern that do not perform photosynthesis. //The xylem of ferns contains only cells called tracheids, long cells to support the plant structure and transport water. Phloem cells include tube-like sieve-tube member cells and companion cells, which allow the flow of water between cells. (DB) (1)//



<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 17px; line-height: 25px;">**Reproduction**

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Ferns and their relatives reproduce via a general reproductive cycle common to all land pants known as alteration of generations, in which there is both a multicellular diploid form and a multicellular haploid form. The majority of a fern’s life is spent in the multicellular diploid form. Following are the basic steps of reproduction of a fern:


 * 1) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Each spore develops into a gametophyte (the multicellular haploid form) that lives by performing photosynthesis. Each gametophyte possesses archegonia (female sex organs) and antheridia (male sex organs) that mature at different times such that cross-fertilization is ensured.
 * 2) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Fertilization occurs when fern sperm use their flagella to swim from the antheridia to the archegonia of another gametophyte.
 * 3) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The fertilized egg develops into a new sporophyte (the multicellular diploid form), and the plant grows.
 * 4) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The cycle starts again when the sporangia of this new sporophyte release their spores.





<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 17px; line-height: 25px;">**Environmental Adaptations**

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Pterophytes, unlike the huge number of plants categorized as angiosperms, do not produce flowers. Therefore, pollination by other animals (like bees, for instance) is not a method by which pterophytes can spread their genetic material. Instead, pterophytes have sporangia supplied with springlike apparatuses that launch the sporangia into the air like projectiles. These sporangia are then carried by the wind to various other locations, where they then release their spores.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; line-height: normal;">//The rhizomes of the maidenhair ferns allow the plant to grow on almost completely bare rock and in areas susceptible to strong runoff after rain. The rhizomes also act as a food store when the fern is unable to photosynthesize during dry/unsuitable conditions. Maidenhair ferns can become dormant and re-grow leaves from the rhizome as well as reproducing asexually when sections of rhizome break off and continue to grow as a new plant. (AK) (2)//

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Horsetails are further adapted to their environment. Since horsetails are generally found in soil that is saturated with water, the oxygen level in that soil is very low. In order for the roots and the rhizome to obtain this necessary oxygen, horsetail stems contain air canals that allow oxygen gas to flow directly from the leaves (that captured the oxygen gas from the air) to the roots and to the rhizome.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Some ferns can live in very bright or very limited temperatures. The Crocodile fern for example, can live in low sunlight or extreme sunlight, due to the odd, croc-skin-like texture of its leaves. (GR)([|14])

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif; font-size: 17px; line-height: 25px;">**Review Questions:**

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">1) What are the three different types of Pterotphyta? (MLK) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">2) What evidence was led to the inclusion of the 3 types of Pterotphyta into they same phylum? (LJ) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">3) Describe the different types of habitats ferns live in, and explain how they have adapted to thrive there. (SM) <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">4) What is the significance in the development of rhizones and roots in ferns? (KS)

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Sources:
<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Reece, Jane B., and Neil A. Campbell. Campbell Biology. San Francisco: Pearson Benjamin Cummings, 2009. Print.

<span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">1. [] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">2. [] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">3. [] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">4. [] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">5. [] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">6. [] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">7. http://www.alientravelguide.com/science/biology/life/plants/tracheo/pteropsi/fernlike.htm <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">8. [] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">9. [] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">10. [] <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">11. http://www.deanza.edu/faculty/mccauley/6a_site_images/plants-images/pteridium-rhiz-vb-300.jpg <span style="font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">12. [] 13. [] 14.http://www.tellys.com/departments/Ferns (GR)