Ferns

Ferns- Part of the Phylum Pterophyta Olivia Roberts-Sano The above picture shows ferns. (CC)[|8] ** Diagnostic Characteristics: ** Ferns belong to a phylum of seedless vascular plants, meaning that they have roots, leaves, and transport systems, but do not have pollen or seeds. The vascular tissue is made up of transport tubes which connect cells and carry water and nutrients. The main character separating ferns from other vascular plants is the reproduction cycle. Ferns instead have spores, and their reproduction cycle is sporophyte dominant. For the most part, ferns are homosporous, having one type of spore, but those ferns that returned to the water during evolution are heterosporous, having two types of spores. Ferns can be confused for seed bearing plants, and, as previously stated, the main difference between the two is in the mechanisms for reproduction. Ferns are less specialized than seed bearing plants to live on land, since their sperm must swim to egg in order to reproduce, so the fern requires moisture for reproduction. Another difference that can be used to diagnose if a plant is a fern is if the fronds (leaves) have sori, which look like red dots and are clustered groups of sporangia, on their underside. (SD) Ferns are commonly found in the tropics and are most diverse there, but many varieties are found in temperate forests. A few can grow in arid environments, but because their gametes use flagella to swim in reproduction, a damp environment is best. The stereotypic images of ferns grow in shady moist conditions of woodland is far from being a complete picture of the habitats where ferns can be found growing. Fern species live in a wide variety of habitats, from remote mountain elevations, to dry desert rock faces, to bodies of water or in open fields. Ferns in general may be thought of as largely being specialists in marginal habitats; however, there are four particular types of habitats that ferns are found in: moist, shady forests; crevices in rock faces, especially when sheltered from the full sun; acid wetlands including bogs and swamps; and tropical trees, where many species are epiphytes (something like a quarter to a third of all fern species).(4)(ZS) Ferns belong to the pterophyta phylum which also includes whisk ferns and horsetails. Water varieties of ferns evolved from water to land but returned to the water at some point. There is also a tall-stemmed fern called the tree fern, the top of which is a crown of fronds. According to a classification system proposed by Smith in 2006 the phylum Pterophyta, or Pteridophyta, can be broken down into four classes. The four classes are Psilotopsida (whisk ferns and ophioglossoid ferns), Equisetopsida (horsetails), Marattiopsida and, Polypodiopsida (leptosporangiate ferns). One way of looking at these classes is that Psilotopsida can be considered "true" ferns and the other three classes can be considered "fern allies".(RL)(10)
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The whisk fern, known as // Psilotum nudum, has a three lobed spore producing structure that is said to be leafless. The aboveground structure of the fern is branched whereas the bottom portion consists of filaments called rhizoids. //Whisk ferns like the warm weather of the tropics and subtropics. They are native to the southeastern region of the United States, Japan, Australia, and New Zealand. Whisk Ferns form large clumps in trees and are occasionally terrestrial in moist well-mulched flower beds. On the other hand, horsetails never developed the ability to reproduce with seeds, and can be found in both the southern and northern locations of the globe.(YA)(5)



(click for larger image. 3)(SM) ** Basic Anatomy: ** Ferns leaves are megaphylls, meaning that they have larger and more leaves than their ancestors. The stems of ferns are often rhizomes, meaning that they run along the ground and bear roots. Large leaves divided into leaflets, called fronds, grow from the rhizomes.

The fronds are the leaf-like structures that are most often seen by observers. The "leaf" of the fronds is called the blade and the "stem" is called the stipe.(KL)([|1]).The organizational pattern for Fern leafs, also called Fronds, is called Pinnate. Pinnate structure means that the leaf has one central axis. This produces lateral structures that are opposite each other along the central axis. Pinnate leaves can either be simple, compound or bicompound. The central axis of compound leafs is also called the Rachis. The leafless portion of the axis that connects the axis to the stem is called the Petiole. (LW) (14)The vascular systems of the fronds are extensively branched. Ferns also can have erect green stems. In horsetails, these erect stems are jointed and serve as the major source of photosynthesis. As vascular plants, ferns contain a xylem, a phloem, and roots which help with the transport of materials.

(9)(MF) ** Transport of Materials: ** Ferns have true roots and lignified vascular tissue. The roots pull up water and necessary minerals from the soil. The phloem brings sugar from sugar heavy photosynthetic areas, called sources, to sinks, areas with little sugar. The xylem brings water and minerals, mostly from the roots, to the rest of the pant. Just like a circulatory system, a transport system in plants is necessary to carry materials through the fern. The xylem transports water from the roots to the top of the fern through a series of connected vessels. These vessels pump the water from the bottom to the top quickly and efficiently. When a tree is cut open, the rings that are seen is left over xylem tissue. From the top, the glucose made by photosynthesis needs to be transported as well. This is done by the phloem. Phloem is always alive, but xylem dies after one year, which is why the rings inside a tree tell how old it is. (NG)(7) ** Reproduction: ** As previously mentioned, ferns have sporophyte dominant reproduction cycles, where the spores are larger than the gametophytes. Sporophytes are diploid cells (having two sets of chromosomes) which divide to produce spores, which are haploid (one set) reproductive cells. Unlike gametes, spores do not need to fuse with other cells to produce an organism. Spore production is done by plant organs called sporangia. On the undersides of fern leaves, clusters of sporangia called sori are arranged in patterns specific to the fern variety. The sporangia release the spores which develop into gametophytes, which have both sex organs. After fertilization and mitosis the fertilized egg develops into a new sporophyte. Sporangia are found on the underside of the fern's fronds, or leaves. They are usually in clusters, known as sori, and are often covered by a clear flap called the indusium. this setup protects the sporangia, while still allowing them to distribute effectively. Each sporangia has an annulus which catapults the spores out of the sporangium itself. After the spores germinate they produce gametophytes called prothalli which contain both antheridia(male gametes) and archegonia(female gametes). (ZXU)([|2]) ** Environmental Adaptations: ** Following the evolutionary trend of moving from water to land, ferns have adaptations that allow them to live more independent of water. The waxy cuticle on fern leaves allows the plant to retain water. The vascular system helps ferns go for longer periods of time without water because roots can pull up water from the soil. The xylem brings water and minerals from the roots to the rest of the pant, making in unnecessary for every cell to be wet. The lignin in the vascular tissue provides the support needed for ferns to grow larger and taller than their nonvascular ancestors, which allows for more light and surface area and therefore more photosynthesis. The phloem is an adaptation that allows for more specialization because not every cell needs to create the “food”. Just as a factory with each person at just one step is more successful than one with each person making the entire product, cell specialization makes production more efficient. The production of lightweight spores instead of seeds is a great adaptation for ferns because the spore can be blown long distances to mature in ne﻿w areas. (CW)(13) ** Review Questions: ** 1. Describe the process ferns go through to transport materials throughout their structure. (SI)  2. How do ferns survive in arid conditions? What environmental adaptations enable them to grow in dry, rocky habitats? (MT)  3. Spores grow into gametophytes which have what sex organ? (MC)  4. What are basic parts of a fern? What are their functions? [MS]  5. What is the significance in the developement of rhizomes and roots in ferns? (KS) ** Sources: ** Campbell, Neil A., and Jane B. Reece. //Biology//. 6th ed. San Francisco: Benjamin Cummings, 2002. Print. 1. [](KL) 2. [] 3. @http://nefern.info/jpgs/notaxa/frndprts.BMP (SM) 4. [|http://en.wikipedia.org/wiki/Fern (ZS)] 5. [|http://www.washjeff.edu/greenhouse/Pnudum/](YA) 6. [] (SR) 7. [] (NG) 8. [] 9. [] (MF) 10.[] (RL) 11.[] (CSR) 12.[] (SD) 13.[] 14.[] (LW)