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Chordata-2 Invertebrate Phyla
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By Eli Keimach
A Fern (1RM)
Ferns are members of the phylum
. Different types can grow anywhere from 2 or 3 millimeters to 10 meters in height (6 J Stein). Ferns have horizontal rhizomes from which large leaves with extensive vascular systems grow. Fern leaves (fronds) are divided into many leaflets. The fern frond grows as its coiled tip, the fiddleback, unfurls. Tree ferns have tall stems with a crown of leaves at the top. On the underside of ferns leaves are clusters of sporangia. This sporangia or sori, can be green leaves or special non green leaves. The arrangement of a fern’s sori is used to aid in plant identification.
The fronds grow in such a fashion that each one looks like the bigger lear, and is a scale image. This is a great natural example of the chaos theory of mathematics, which deals with patterns like the fern. (JE)
Ferns are the most widespread and diverse of all the pteridophytes. Although they are most diverse in the tropics, they can also be found in temperate forests and even arid conditions. Some ferns have adapted to dry habitats, but most prefer the shady, moist environment of woodlands. They are found in abundant amounts in tropical rain forests (7 JSun).
Generally, there are four particular types of habitats that ferns are found in: moist, shady forests; crevices in rock faces (sheltered from the sun), acid wetlands, and tropical trees. (DC 13)
The vascular system was a major evolutionary adaptation in the ferns that made them better suited for dry environments (16T2).
Three groups of plants have been considered ferns: two groups of eusporangiate ferns, ophioglossaceae and marattiaceae, and the leptosporangiate ferns. The marattiaceae group is a primitive group of tropical ferns with fleshy rhizomes and are now thought to be a sibling to the leptosporangiate ferns. Eusporangiate ferns are more primitive, stout, and thick-walled than leptosporangiate ferns. ( 17 AN) This is because Eusporangiate ferns lack the
, or ring of thickened cells that is present in more advanced ferns like the leptosporangiate ferns. (17 AN)
(Leptosporangiate Fern) (12 VK)
(Ophioglossaceae Fern) (12 VK)
(Marattiaceae Ferns) (12 VK)
Roots- The underground structures that take up water and nutrients from soil are always fibrous and are structurally very similar to the roots of other plants.
Prothallus- An extremely thin structure that produces the fern’s gametes
Leaf- The green, photosynthetic part of the plant. In ferns, leaves are referred to as a frond. New leaves typically expand by the unrolling out of a spiral called a crozier or fiddlehead.
Stem- Either an underground or above ground semi-woonden trunk. The stem has distinct vascular bundles - each bundle has xylem and phloem (found toward the inside and outside, respectively) (CS 14).
Sporangium- A sac-like structure in which fungal spores are formed (KA).
Annulus- ring of cells around the sporangium of some ferns. These cells help aid spore dispersal by becoming progressively thicker, inducing tension and eventually causing the sporangium to rupture (KA).
anatomy of fern (1DO)
Transport of Materials:
Similarly to other plants, ferns use a xylem to transport water and a phloem to carry organic materials. This characteristic of using a xylem separates Pteridophyta (ferns) and Byrophytes (mosses). (12-SC)
Sori, or sporangia, can be found on the undersides of sporophylls. Sporangia are miniature sacks or capsules that produce the dustlike spores that are the seeds which ferns stem from. A sorus refers to multiple sporangia found in a group. (2 AW) Most fern sporangia have a spring-like mechansim that can launch spores several meters.
One mechanism for spore dispersal of ferns relies on cohesion. As water evaporates from the cuplike dead cells, the sporangium bends until the force is too great to be held by the cohesion of the water, at which point the sporangium snaps forward, releasing the spores (DPOD 5).
Spores are the main form of dispersal for ferns. Ferns reproduce with spores that develop on the underside of leaves. Spores are scattered by the wind, and one that falls in a moist environment may grow into a tiny heart-shaped "prothallus," which is the sexual or gametophyte stage of the fern (1 MB). Spores are normally formed in groups of four. Spores contain oil droplets and sometimes chlorophyll in addition to their nucleus. Ferns drop millions, often times billions of spores during their lifetime, but many of these seeds do not land in ideal environments. (2 AW)
(SW 8:) There are two distinct stages in the life cycle of ferns. The fern that we are familiar with is the adult, diploid sporophyte, a generator of spores. The spores germinate and grow into haploid gametophytes, which in turn produce gametes. When the eggs are fertilized, they develop into the adult fern, and the cycle perpetuates.
Life cycle of ferns (6 HL)
Ferns first appear in the fossil record in the Devonian period. By the Triassic period the first evidence of ferns related to several modern families appeared. In the late Cretaceous period many of the modern families of ferns first appeared.
Ferns are thought to have evolved from green algae and from their divergence, ferns developed various adaptations that allowed them to increase in size and complexity. For example, ferns became less dependent on a watery environment because they developed rhizomes (subterranean stems) and their roots that could hold water and carry it through the fern via an efficient vascular system. Leaves were also developed for photosynthesis. (8 AS) Many ferns are drought resistant, and can grow in the shade or the sun. While most are many are in tropical climates, many others are found in temperate and alpine climates. Ferns have evolved to be flexible. However, all ferns must live near a source of water as that is how they reproduce; thus there are no ferns that live in dry climates. This is one factor that separates them from gymnosperms and angiosperms. (AR 12) Ferns in temperate regions have stems (called rhizomes) that grow underground, whereas ferns in the tropics have stems that grow above ground and can reach hights of up to 40 feet (EG).
1. What is the significance in the developement of rhizomes and roots in ferns? (10 AL)
2. What is the significance of the arrangement of a fern's sori? (EK)
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