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Evolution of H2O Conservation Methods in "Equisetum"

Introduction:
From as far back as the Devonian, fossil predecessors of Equisetum have shown progressive methods of water conservation. Presumed to have originated during a fairly wet period of Earth's history, the repetitive cycling of moist and dry conditions in the areas where Equisetum ancestors flourished enabled the evolution of several family-specific characteristics. These include thickened cells constituting the outer walls, the fusion of leaves into a sheath surrounding the main stalk of the plant, and the incorporation of silica into the stems.

Equisetum Ancestors:
Phylogenetic research into the origins of Equisetum has lead to a probable first ancestor. It is now hypothesized that the Trimerophytophyta were the family from which all sphenophytes are derived. Arising in the Devonian era, trimerophytes consisted mostly of wholly photosynthetic branching stems, lacking all root and leaf structures. Their branching was unequal, leading to the appearance of a main axis with several smaller lateral offshoots. Vascular tissue had evolved by now, forming a protostele within the trimerophytes (Stewart, 210). All of the trimerophyte vascular systems are composed of a three-ribbed protostelic system throughout with the exception of the extreme appendages. The vascular tissues begin in the center of the stem and grow outward. When one of the strands crosses an area where a lateral branch occurs, it begins to enlarge in the direction of the branch, resulting in the ribbing of the stem. (Wright, 209).
The arrangement of the branches in a trimerophyte is unique. In the plant families ancestral to it, all extensions arise as a dichotomously branching. The trimerophytes brought about a new method. Lateral branches arise in a fashion similar to the whorled leaves of the modern horsetail with a notable exception. The branches stem out from the main axis in a "staircase" arrangement, the lateral extensions coming off of the stem at one point with the next one growing a certain distance around the stem and slightly higher up (Stein, 108).
In the middle Devonian, Trimerophytophyta gave rise to Ibyka, a cryptic genus found in the eastern parts of the United States. Morphologically, Ibyka is similar in appearance to the trimerophytes. The plant is composed of the same sort of branching system with the lateral branches arising from the main stem in a spiral form. It's been determined that the width of the

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