SporePlants213-page12

SporePlants213-page12 - of the Equisetales The Equisetums...

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Spore-Dispersing Vascular Plants - 12 Equisetales There is one living genus in the Equisetales: Equisetum . Equisetums are commonly called horsetails or scouring rushes; the first because some seem to look like horses' tails, the second because they were used to scour pots by many peoples. Though not conspicuous, they are quite abundant throughout the world. None exceeds about 15 feet in height; one species in Washington can reach more than 6 feet. The Equisetales are very important in the fossil record, and members of the Equisetales were once the predominant plants in the landscape. Coal is derived from fossil Equisetum relatives as well as from the fossil Lycophytes. The current is indistinguishable from its fossil ancestors, and some believe it to be the oldest surviving genus of plants (300 million years old). Characteristics
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Unformatted text preview: of the Equisetales The Equisetums may be the most distinctive plants on earth. They have hollow, jointed stems that are impregnated with silica. This gives a rough texture, and is the source of the common name for some Equisetums, scouring rushes. Some Equisetums have whorled axillary branches at the stem joints (which are really the nodes). The axillary branching fools some into thinking the branches are jointed leaves. They are not. The aerial stems arise from nodes of persistent below-ground rhizomes. The rhizomes allow survival in harsh environmental conditions. The mature stems have a hollow pith and two rings of canals in the cortex. The innermost canal, the carinal canal, has xylem and phloem and is used in conduction. The larger, outer canal is air-filled....
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