Plants-GymnospermsKingdom: Plantae
Phyla: Gymnosperms


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A forest densely populated with conifers, a phyla of gymnosperms.
http://www.nasa.gov/centers/goddard/images/content/156030main_Conifers_JPG.jpg//


~Ethan R

Introduction and Diagnostic Characteristics:


Gymnosperms are plants adapted to live on land - thus, they are autotrophic, photosynthetic organisms that tend to conserve water. They have a vascular system, used for the transportation of water and nutrients, that includes roots, xylem, and phloem. This system will be discussed further in "Transportation of Materials."
Gymnosperms are seed plants. The name gymnosperm means "naked seed," which is the major distinguishing factor between gymnosperms and angiosperms, the two distinct subgroups of seed-plants. This term comes from the fact that the ovules and seeds of gymnosperms develop on the scales of cones, rather than in enclosed chambers called ovaries. Too, gymnosperms are older than angiosperms on the evolutionary scale. They are found far earlier on the fossil record than angiosperms, and as you will see from the various environmental adaptations gymnosperms made, gymnosperms represent a step in the path to the most successful (diversity-wise) clade (monophyletic branch), angiosperms. (1)




Habitats:


Because of their excellent ability to conserve water, gymnosperms are fairly well suited to drier climates. While gymnosperms would be found more widely, the success of angiosperms has pushed gymnosperms to populate the more extreme regions (ie: higher altitude, colder temperatures). Conifers, the major phylum of gymnosperms, dominate the forrests of the Northern Hemisphere. (1) However, gymnosperms occur in both the Southern and Northern Hemispheres (7, DJ). In fact, the cypress family or the Cupressaceae, the most widely distributed of all gymnosperms, lives on all continents except for Antartica (7, DJ).
external image the%20old%20cypress%20tree,%20over%20the%20bridge,%20luckenbach.JPG
A cypress tree in South America. (VM)




Major Types:


There are 4 significant phyla of gymnosperm, three of which are relatively small.

Phylum Ginkgophyta:

Ginkgo trees maintain a green leaf color in the summer and a gold color in autumn. Female Ginkgo trees produce fleshy seeds known for the stinky odor they produce when decaying. For this reason, landscapers typically plant only male Ginkgo trees (1). Ginkgo trees are credited as being native to China, but there is some mystery as to whether or not the trees grow in the wild (2) (DP). Ginkgo trees may have evolved early when the Earth's atmosphere was not very hospitable to life and when volcanic eruptions were frequent. This might be why they survive well in places with pollution. Ginkgo trees differ from other gymnosperms in that they are deciduous, meaning that they lose their leaves in the fall. Although their leaves are flat like those of true deciduous trees, the veins are neither parallel (running side by side) or net-like (like those on a maple tree). Rather, they fan out from the point at which the leaf is joined to the twig (8) [HZ].

Phylum Cycadophyta:

The Cycad phyla of gymnosperms has a similar appearance to palms, though palms are flowering plants while Cycads are not (1). They are found in tropical and subtropical areas, although some species can live in areas that receive frost. The Phylum Cycadophyta contains one Class, Cycadopsida Brongn, which contains one Order, Cycadales Dumort. All species of Cycadophyta have blue-green algae in their roots that help convert nitrogen into a usable form (2) (DP).
Many tropical cultures find the symbiotic uses of the cycads very useful, but the cycads also produce a toxin that is very toxic to livestock. In addition, Cycads reproduce by means of either swimming sperm or insects, a fairly advanced feature of gymnosperms. (5)(RJS)

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example of a cycad (OZ)

Phylum Gnetophyta:

There are three different genera (genus, but plural) in the phylum gnetophyta, though each are quite different in appearance. Welwitschia has elongated strap-like leaves, Gnetum grow in the tropics as trees or vines, and Ephedra is a shrub of the American deserts (1). Species in Gnetophyta appear to resemble angiosperms more than gymnosperms, due to their flower-like reproductive structures, and were once thought to be a group of angiosperms that evolved separately. However, because of modern molecular data, Gnetophytes are in a "sister group" to conifers (2) (DP).

The biggest of the 4 phyla of gymnosperm is the conifer, of...

Phylum Coniferophyta (or Pinophyta):

While all gymnosperms have roughly cone-like structures used in reproduction, conifers are known for and named for their cones (the name conifer means "carrying a cone"). Included in this phyla are pines, firs, spruces, larches, yews, junipers, cedars, cypresses, and redwoods, all of which are typically large, except for those at higher altitudes. There are roughly 550 species of conifers, though just a few of them are commonly seen in the forests of the Northern Hemisphere.
Many conifers are evergreens - they do not lose their leaves in a cyclical manner but retain them all year long. Their leaves often are scales or needles (very thin leaves as show in the background of the picture of the seed bearing cone.) [3] (SV) This strategy is used so that the conifers can perform some minor photosynthesis in the winter and so they can have fully developed leaves for the first sunnier days of the spring. Examples of conifers that drop leaves in the fall (and thus are deciduous) are the dawn redwood and tamarack.
Conifers are the biggest and oldest organisms on our planet. One bristlecone, named Methuselah, is more than 4,600 years old! (1)
external image western-larch-tree-fall2.jpg
http://www.bentler.us/eastern-washington/plants/trees/western-larch-tree-fall2.jpg
Above is an example of a Larch tree. It has needles and is large, like most of the other trees in the Coniferophyta phylum. (AR)



Basic Anatomy:


As modern vascular plants, gymnosperms use food-transporting phloem and water-conducting xylem tissue. Additionally, gymnosperms have true roots in order to collect water and nutrients from the ground. Gymnosperms are leaved plants, though their leaves generally have less surface area in order to minimize water-loss. Gymnosperms are seed-bearing plants, and conifers specifically utilize closely packed sporophylls that together form cones. (Other varieties of gymnosperms cluster the sporophylls together but usually from fruit-like structures instead of cones.) [3] (SV)
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A seed-bearing cone hanging from a pine.
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While conifers are typically tall, other phyla of gymnosperms vary greatly in their shape. (1)



Transport of Materials:

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A closer look at the xylem and phloem of the vascular transport system of a gymnosperm.
(6 SES)

As aforementioned, gymnosperms use a vascular transport system to carry water and nutrients to all parts of the plant. The intake of water and nutrients begins at the roots of the gymnosperm, which diffuse into the ground in order to maximize the amount of water and nutrients collected. The water and nutrients collected by the roots are distributed throughout the plant by the vascular tissue, where cells are joined into tubes. The small diameter of the tubes facilitates the flow of materials by allowing for "capillary action," in which the materials are pulled up the tubes (mainly due to water's innate properties of cohesion and adhesion). The stems which h off of carry the water and nutrients to the leaves and move the sugar produced by the leaves away. The vascular tissue involved in plant transport of materials can be broken into 2 main types: xylem and phloem. Xylem transports water throughout the plant (interesting fact: the cells that make up xylem are actually dead!), and phloem transports food. (1)



Reproduction of Conifers:


Gymnosperms are sporophytes (a plant with 2 copies of its genetic material, capable of producing spores). Their sporangia (receptacle in which asexual spores are formed) are found on sporophylls, plated scale-like structures that together make up cones. The female gametophyte develops from the haploid (meaning 1 set of genetic material, DNA) spores that are contained within the sporangia. Like all plants, gymnosperms are heterosporous, specifically for gymnosperms, both sexes of gametophytes develop from 2 different types of spores produced by 2 separate cones. One type of cone is the small pollen cone, which produces microspores, which subsequently develop into pollen grains, or male gametophytes. The other type of cones, the larger "ovulate" cones, make megaspores that develop into female gametophytes. Incredibly, this whole sexual process can take three years, from the production of the two sexes of gametophytes to bringing the gametophytes together in the process of polination, and finally to forming mature seeds from fertilized ovules. After this process is completed, the individual sporophylls separate (the cone breaks apart) and float in the wind to a (hopefully) habitable place. This is concluded with germination and the formation of a seedling. Conifers have sperm that do not have flagella, but instead are conveyed to the egg via a pollen tube. (7 KN) It is important to note that the seeds of gymnosperms are unenclosed in their final state upon the cone. This is significant because the term gymnosperm comers from the greek word gumnospermos//, meaning "naked seeds". (7 Nangia)


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The reproductive cycle of a gymnosperm.
http://dbs.umt.edu/courses/sci226/gifs/images/lab4/img7_large.gif




Environmental Adaptations:


The phyla of gymnosperms arose during the Carboniferous and early Permian periods. As the supercontinent Pangaea formed, it is possible that the interior of the continents got drier, as there was less coastal land. Thus, gymnosperms adapted to make good use of the water that was available to them. The needle shaped leaves of pines and firs are adapted to dry conditions, as a cuticle (outer layer of living tissue) covers the leaf and the stomata (pores in the leaf) are found in pits. Since seedless reproductive mechanisms generally require water, the adaptation of seed use was another step in the move away from dependence on water. An additional environmental adaptation is the great height of the conifers, which allows for improved spreading the fertilized sporophyls that are released when the cone breaks apart. (1) A variety of gymnosperms are adapted to rather severe climate conditions. Since these conditions usually result in a dry environmental, gymnosperms have several adaptations that allow them to survive in those habitats through conservation of water. Although there is a fairly wide variety of adaptations, these are some of the more prominent examples: a waxy cover and pores deep in the leaf surface are used to prevent evaporation of valuable water (4, NK). In particular, conifers are more common in cooler regions and in xeric, or extremely dry, habitats. Because of their leaf and stem anatomy they are better adapted to drought than most broadleaved trees. Additionally, many conifers have evolved to become durable in cold weather so that the above ground structures can continue to function even in harsh environments. (5) (SS)

54672205.GulmargDay12565SnowMountainView.jpg<http://i.pbase.com/g3/62/629762/2/54672205.GulmargDay12565SnowMountainView.jpg>. This pictures demonstrates one of the environmental adaptations of conifer trees: adaptations to severe climates. Conifers have adapted to the temperatures of snowy mountains, an environment where a severe snow storm could always hit. However, conifers are able to survive in these climates by their ability to conserve water! (Jesse Carmen)

Importance of Gymnosperms on Humans and Ecology:

Some of the oldest things on earth are redwood trees and bristlecone pines, both of which are gymnosperms. Not only do gymnosperms live in the wild, but they also tend to decorate the homes and gardens of many human households. Also, most of the wood we use to build houses and other things that lumber is used for are from gymnosperms. Many species of gymnosperm are used to create certain medicinal substances (10 BL). Below is an example of a Redwood tree. It is evident that it is very important to preserve these great trees(SJB)
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5-05 Eddie Redwood Forest -sm.JPG.jpg
http://www.awsumb.com/images/5-05%20Eddie%20Redwood%20Forest%20-sm.JPG



Review Questions:
1. List and describe the biggest of the four phyla of gymnosperms. (YS)
2. Relate the structure and anatomy of gymnosperms to their function. (RK)
3. Describe the structure and function of the water and nutrient transport system of gymnosperms. (HS)
4. What are the major unique features in gymnosperms that are different from other phyla? (JAC)
5. Discuss the various environmental adaptations that gymnosperms have made to be able to survive in cold conditions.(GR)
6. Explain how gymnosperm reroduction is similar and different to other types of plants. (BMB)


Works cited:
1) Campbell, Neil A., and Jane B. Reece. Biology. 6th ed. Boston: Benjamin-Cummings Company, 2002
2)
Earle, Christopher J. "Gymnosperms." The Gymnosperm Database. 30 Nov. 2008 <http://www.conifers.org/>.
3)http://botit.botany.wisc.edu/courses/systematics/Phyla/Phylum_directory.html
4)"gymnosperms." Geocites. 3 Dec. 2008 <http://www.geocities.com/heartland/plains/6761/ecycads.htm>.
5) "Gymnosperms." Hort & Crop Science. The Ohio State University. 7 Dec. 2008 <http://hcs.osu.edu/hcs300/gymno.htm>.
6) "The Vascular Bundle." Photosynthesis. 7 Dec. 2008. <www.hobart.k12.in.us/ jkousen/Biology/phobig.html>
7) Earle, Christopher J. "Cupressacae." The Gymnosperm Database. 31 Jul. 2008 <http://www.conifers.org/>.
8) Conrad, Jim. "The Ginkgo." Backyard Nature. 13 Dec. 2008 <http://www.backyardnature.net/ginkgo.htm>.
9) 15 Dec 2008 <http://2bits.ca/images/journal/on%20to%20texas/the%20old%20cypress%20tree,%20over%20the%20bridge,%20luckenbach.JPG>10) "gymnosperm." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 17 Dec. 2008 <http://www.britannica.com/EBchecked/topic/250316/gymnosperm>.

Page Edited by: DP, Sarah Vlach, NK, SS, Sarah Schwarzschild, Daisy Joo, Hanna Zhu, Kevin Nayer, Hilary Stepansky, Josh Czik, Vonai Moyo, Becca Levenson, Sam Blatchford, Meru Nangia, Brittany Marcus-Blank