Gymnosperms

Gymnosperms by Walker Keenan
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Ginkgo from the phylum Ginkgophyta.

Pun: “Can’t see the gymnosperms for the angiosperms.”

Definition: A **vascular plant** (a plant that carries water and other resources up and down the plant body) that bears **naked seeds not enclosed in specialized chambers** (ovaries).Gymnosperms are broken into **four phylum** **Ginkgophyta, Cycadophyta, Gnetophyta, and Coniferophyta.** They get there name from the Latin word meaning "naked seed" because, unlike angiosperms, their seeds are not protected by the ovaries of the plant, otherwise known as fruit.(JAS)

Diagnostic Characteristics: One way to see if a plant is a gymnosperm is to see whether it loses its leaves (with the exception of the tamarack & dawn redwood and a few others, this is true). In addition, almost all gymnosperms have needles as leaves with the exception of the ginkgo as pictured above. A common gymnosperm that may be familiar to you is the ginkgo, which is commonly grown in urban settings whose leaves turn golden in the fall. Another common example is the pine tree. If you see that the plant flowers, it is not a gymnosperm. The most common gymnosperms are in the conifer phylum. These include cedars, pines, junipers, firs redwoods, and many more. Gymnosperms are also vascular plants meaning they transport water, minerals, and sugars throughout their bodies with a xylem and phloem. The **Xylem** carries water and nutrients from the roots up throughout the plant, while the **phloem** delivers sugar throughout the plant. Instead of seeds, gymnosperms have spores created and stored in the **sporangia**.[A sporania is a plant, fungal, or algal structure that is capable of producing and containing spores.RS []]. **Seeds** vary from **spores** in the fact that seeds have stored food and resources and that spores have little of this. However, Gymnosperms are seeds right before they turn into sporophytes during the zygote phase. Another way to tell if a plant is a gymnosperm is to see if it has cones. If it has cones, it is probably a gymnosperm since all species in the phylum Coniferophyta, which are gymnosperms, have cones. Habitat: Gymnosperms vary in habitat. Some gymnosperms from the genera Welwitschia from the phylum Gnetophyta only grow in certain areas; this plant only grows in the deserts of southwestern Africa. Some gymnosperms are seen in cities around the world like the ginkgo tree (the only surviving species of phylum Ginkgophyta). Plants in the genera Gnetum in the Gnetophyta are often found in tropical climates while some gymnosperms like the plants in the Ephedra genera of the phylum Gnetophyta thrive all around the world.

Major Types: In the category of gymnosperms, there are four phylum, Ginkgophyta, Cycadophyta, Gnetophyta, and Coniferophyta. The phylum that contains the most species and most well-known species is the Coniferophyta phylum. Many pines, firs and redwoods are in this category The Ginkgophyta only contains one species, the ginkgo. The Cycadophyta phylum contains species that look like palm trees. These plants are seen in many different enviroments, but are mainly restricted to tropical climates. One other characteristic common to this phylum is that they have coralloid roots (light colored, club shaped structures that assist in nitrogen fixation). (LD) The phylum Gnetophyta has three genera the Edpheras, the Gnetums, and the **Welwitschia**. The **Edpheras** are shrubs while **Gnetums** are tropical vines and Welwitschia have large strap like leaves. Gymnosperms can also be divided into families. The major families of gymnosperms include: Pinaceae (Pine Trees), Cupressaceae (Cypress), Ephedraceae (Mormon Tea; includes a variety of shrubs), Ginkgoaceae (Ginko), Taxaceae (Yew Family), and Zamiaceae (Cycas Trees; include tropical palm trees). (JAF) Trees from the family Pinaceae include the giant sequoias, which are the world's largest trees and may weigh up to 4.4 million pounds.The Bristle Cone Pines are over 4000 years old. They are the oldest living plants. (JJF) Redwood trees are also of the family Pinaceae; these are the tallest trees and may be more than 110 meters tall. Both of these species are commonly found in California. (SF) Basic Anatomy: In the female reproductive cones (all woody cones are female cones) there are two ovules in the middle and specialized leaves (**sporophylls**) on the outside The sporophylls are the leaves that make up the woody cone. The male cones are very small and have **pollen** (which produce male gametes) under their own modified leaves like the ones female cones have. Transport of materials: The gymnosperm is a vascular plant meaning water and nutrients are sent throughout the body using **x****ylem** and **phloem**. Xylem and phloem are tissues found in vascular bundles, much like veins and arteries, that carry materials throughout the plant. These tissues extend from the leaves all the way down to the roots of the plant (KNS). Water and minerals are sent up through the plant by the xylem while sugars are sent through the plant by the phloem. diagram of xylem and phloem (JL)

Reproduction: **Sporophytes** are trees or organisms that resulted from the union of two haploid gametes into one diploid organism that produces haploid spores, starting the cycle again. The sporophytes contain the female and male cones.

(APS) As described earlier, the **female cones** are the larger ones with two ovules in the middle and specialized leaves (sporophylls) on the outside while the **male cones** are much smaller and have many **microsporangia** (very small sporangia) underneath sporophylls in the cone. Micro spores are produced in the sporangia of male cones and they develop into **pollen grains,** which are **haploid** (half the chromosomes of the original). The female has a **megaspaorangiua** (large sporangium) in each ovule. The fertilization can take up to 12 months. During the fertilization, one of the female cone's four cells with one set of chromosomes survives. This haploid cell turns into a mega spore and grows into a gametophyte which contains one set of chromosomes. Inside the gametophyte, there are a few archegonia (the part of the gametophyte that holds the actual gamete). The pollen grain has already reached the female gametophyte by this time. When the pollen grain has attached itself to the female gametophyte, it puts a sperm nuclei into the egg. After fertilization, the plant goes from being an embryo (when the process has reached this state it is a seed) to a zygote, and back to being a sporophyte. This sporophyte develops into its mature form over time. [It initially developes in the middle of a female gametophyte. The gametophyte provides the new sporophyte with food until it eventually: gains a protective seed coat from the remains of the megasporophyll left over from the original pinecone and even a feature which allows it to travel through the wind. Once this is aquired and the seed has matured, it will detach itself from the female cone and allow the wind to bring it to a new place. After it lands and germinates, it will feed off of the female gametophyte until its leaves have surpassed the surface of the ground and can perform photosynthesis. (DG)]. [Gymnosperms are polycots (many cotyledons), which is determined by their "naked" seeds. No fruit is produced to hide the seed, but many little leaves grow around the embryo before it sprouts. (BY)]

[Microspores and megaspores are formed on sporophylls in male and female cones respectively. Each scale in the male cone has two sporangia in which meiosis occurs to produce tetrads of spores, just as in a fern sporangium.RS []]

Reproduction of a Pine Environmental Adaptations: Gymnosperms have primarily adapted because the **angiosperms** (vascular plants that have flowers and fruit as their reproductive organs) have outcompeted gymnosperms for land and resources. The **fundamental niche** (the entire area where an organism(s) can survive) is practically the whole world. Different gymnosperms can live in different climates and conditions, but as a whole gymnosperms can live around the world. However, the flowering angiosperms outcompete the gymnosperms and take over much of their fundamental niche. The **realized niche** (the actual area in which a species lives after **resource partitioning** (the splitting of resources by species as a result of competition)) for the gymnosperms for the most part has been pushed to fringe areas on the planet. These areas are often temperature extremes and gymnosperms have been able to survive there. For example, welwitschia plants are able to grow in the harsh climates of southwestern African deserts and the tamarack grows in the tundra at bitterly cold temperatures.

Review Questions: What are the functions of the xylem and phloem? (KTD) Define, in context, the terms diploid and haploid. (AG) Briefly explain the four Gymnosperms phylum.(CP) Explain the difference between the male and the female reproductive anatomy. (AK) What are the differences between the female cones and the male cones? (SW) Contrast gymnosperms and angiosperms. Why have these differences arisen? (LS) How have the gymnosperms adapted their niches in response to being outcompeted by angiosperms? (AZ) What has caused gymnosperms to be pushed to "fringe areas" on the planet? What are two examples of such gymnosperms? (AS) What are some of the major families of gymnosperms and where can each be found? (JM)

__**Sources:**__


Campbell, Neil A., and Jane B. Reece. __Biology__. Sixth Edition. Boston: Benjamin-Cummings Company, 2002.

[] (Jake Schwartz) [] [BY] [] (JAF) http://www.britannica.com/EBchecked/topic/132725/conifer (Sarah Fleming) []( APS) [] (DG) [] (LD) http://www.life.umd.edu/classroom/BSCI124/lec19.html (KNS) http://kvhs.nbed.nb.ca/gallant/biology/xylem__phloem.jpg (Jesse Landy) http://www.cavehill.uwi.edu/FPAS/bcs/bl14apl/gym1.htm (JJF)