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Stele (biology)
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<h2 id="protostele">Protostele</h2> <p>The earliest <a href="/facts/Vascular_plant/5nWI2huT">vascular plants</a> had stems with a central core of vascular tissue.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a><a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> This consisted of a cylindrical strand of <a href="/facts/Xylem/6lovdKuF">xylem</a>, surrounded by a region of <a href="/facts/Phloem/I34nY0gF">phloem</a>. Around the vascular tissue there might have been an <a href="/facts/Endodermis/CjfaLzdU">endodermis</a> that regulated the flow of water into and out of the vascular system. Such an arrangement is termed a protostele.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p><p>There are usually three basic types of protostele: </p> <ul><li>haplostele – consisting of a cylindrical core of xylem surrounded by a ring of phloem. An endodermis generally surrounds the stele. A <a href="/facts/Xylem_development/6lovdKuF">centrarch</a> (protoxylem in the center of a metaxylem cylinder) haplostele is prevalent in members of the rhyniophyte grade, such as <i><a href="/facts/Rhynia/3XRN8WGd">Rhynia</a></i>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></li> <li>actinostele – a variation of the protostele in which the core is lobed or fluted.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> This stele is found in many species of club moss (<i><a href="/facts/Lycopodium/LhqjEerH">Lycopodium</a></i> and related genera). Actinosteles are typically <a href="/facts/Xylem_development/6lovdKuF">exarch</a> (protoxylem external to the metaxylem) and consist of several to many patches of protoxylem at the tips of the lobes of the metaxylem. Exarch protosteles are a defining characteristic of the lycophyte lineage.</li> <li>plectostele – a protostele in which plate-like regions of xylem appear in transverse section surrounded by phloem tissue, thus appearing to form alternating bands.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> These discrete plates are interconnected in longitudinal section. Some modern club mosses have plectosteles in their stems. The plectostele may be derived from the actinostele.</li></ul> <h2 id="siphonostele">Siphonostele</h2> <p>Siphonosteles have a central region of ground tissue called the <a href="/facts/Pith/luGP442D">pith</a>, with the vascular strand comprising a hollow cylinder surrounding the pith.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> Siphonosteles often have interruptions in the vascular strand where leaves (typically megaphylls) originate (called leaf gaps). </p><p>Siphonosteles can be called <i>ectophloic</i> (phloem present only external to the xylem) or they can be <i>amphiphloic</i> (with phloem both external and internal to the xylem).<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Among living plants, many ferns and some <a href="/facts/Asterid/dQK3vQS5">Asterid</a> flowering plants have an amphiphloic stele. </p><p>An amphiphloic siphonostele can be called a <i>solenostele</i>, or this term may be used to refer to cases where the cylinder of vascular tissue contains no more than one leaf gap in any transverse section (i.e. has non-overlapping leaf gaps).<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> This type of stele is primarily found in <a href="/facts/Fern/e6Cngdyo">fern</a> stems today. Where there are large overlapping leaf gaps (so that multiple gaps in the vascular cylinder exist in any one transverse section), the term <i>dictyostele</i> may be used.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> The numerous leaf gaps and leaf traces give a dictyostele the appearance of many isolated islands of xylem surrounded by phloem. Each of the apparently isolated units of a dictyostele that serve a single leaf can be called a <i>meristele</i>.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> Among living plants, this type of stele is found only in the stems of ferns. </p><p>Most seed plant stems possess a vascular arrangement which has been interpreted as a derived siphonostele, and is called a <i>eustele</i> – in this arrangement, the primary vascular tissue consists of <a href="/facts/Vascular_tissue/Xt3VtbKz">vascular bundles</a>, usually in one or two rings around the <a href="/facts/Pith/luGP442D">pith</a>.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> In addition to being found in stems, the eustele appears in the <a href="/facts/Root/x2U60Gdm">roots</a> of <a href="/facts/Monocot/mXCuuCYo">monocot</a> flowering plants. The vascular bundles in a eustele can be collateral (with the phloem on only one side of the xylem) or bicollateral (with phloem on both sides of the xylem, as in some Solanaceae). </p><p>There is also a variant of the eustele found in monocots like <a href="/facts/Maize/lJ6c5xMH">maize</a> and <a href="/facts/Rye/LwdwSNcp">rye</a>. The variation has numerous scattered bundles in the stem and is called an <i>atactostele</i> (characteristic of monocot stems). However, it is really just a variant of the eustele.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a><a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Vascular_tissue/Xt3VtbKz">Vascular tissue</a></li> <li><a href="/facts/Vascular_bundle/m2x5jxoa">Vascular bundle</a></li></ul> <h2 id="citations">Citations</h2> <ul><li><a href="/facts/Chester_A._Arnold/aDV7uBbc">Arnold, Chester A.</a> (1947). <a href="https://archive.org/details/in.ernet.dli.2015.270777"><i>An Introduction to Paleobotany</i></a> (1st ed.). New York and London: McGraw-Hill Book Company.</li> <li>Beentje, Henk (2010). <i>The Kew Plant Glossary</i>. Richmond, Surrey: <a href="/facts/Royal_Botanic_Gardens%2c_Kew/XN0rTTRv">Royal Botanic Gardens, Kew</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-1-84246-422-9.</li> <li><a href="/facts/Harold_Charles_Bold/yvl3GaH9">Bold, Harold C.</a>; Alexopoulos, Constantine J. & Delevoryas, Theodore (1987). <i>Morphology of Plants and Fungi</i> (5th ed.). New York: Harper & Row. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-06-040839-1.</li> <li><a href="/facts/Adriance_S._Foster/UMrF5Tln">Foster, A. S.</a> & Gifford, E. M. (1974). <a href="https://archive.org/details/comparativemorph00fost"><i>Comparative Morphology of Vascular Plants</i></a> (2nd ed.). San Francisco: W. H. Freeman. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 978-0-7167-0712-7.</li> <li>Gifford, Ernest M. & <a href="/facts/Adriance_S._Foster/UMrF5Tln">Foster, Adriance S.</a> (1988). <i>Morphology and Evolution of Vascular Plants</i> (3rd ed.). New York: W. H. Freeman and Company. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-7167-1946-0.</li> <li>Stewart, Wilson N. & Rothwell, Gar W. (1993). <i>Paleobotany and the Evolution of Plants</i> (2nd ed.). Cambridge: Cambridge University Press. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-521-38294-7.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Foster & Gifford (1974), p. 58. - Foster, A. S. & Gifford, E. M. (1974). Comparative Morphology of Vascular Plants (2nd ed.). San Francisco: W. H. Freeman. ISBN 978-0-7167-0712-7. <a href="https://archive.org/details/comparativemorph00fost" target="_blank">https://archive.org/details/comparativemorph00fost</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Gifford & Foster (1988), p. 42. - Gifford, Ernest M. & Foster, Adriance S. (1988). Morphology and Evolution of Vascular Plants (3rd ed.). New York: W. H. Freeman and Company. ISBN 0-7167-1946-0. <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Bold, Alexopoulos & Delevoryas (1987), p. 320. - Bold, Harold C.; Alexopoulos, Constantine J. & Delevoryas, Theodore (1987). Morphology of Plants and Fungi (5th ed.). New York: Harper & Row. ISBN 0-06-040839-1. <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Stewart & Rothwell (1993), pp. 85–89. - Stewart, Wilson N. & Rothwell, Gar W. (1993). Paleobotany and the Evolution of Plants (2nd ed.). Cambridge: Cambridge University Press. ISBN 0-521-38294-7. <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Gifford & Foster (1988), p. 44. - Gifford, Ernest M. & Foster, Adriance S. (1988). Morphology and Evolution of Vascular Plants (3rd ed.). New York: W. H. Freeman and Company. ISBN 0-7167-1946-0. <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Arnold (1947), pp. 66–68. - Arnold, Chester A. (1947). An Introduction to Paleobotany (1st ed.). New York and London: McGraw-Hill Book Company. <a href="https://archive.org/details/in.ernet.dli.2015.270777" target="_blank">https://archive.org/details/in.ernet.dli.2015.270777</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Beentje (2010), p. 7. - Beentje, Henk (2010). The Kew Plant Glossary. Richmond, Surrey: Royal Botanic Gardens, Kew. ISBN 978-1-84246-422-9. <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Beentje (2010), p. 89. - Beentje, Henk (2010). The Kew Plant Glossary. Richmond, Surrey: Royal Botanic Gardens, Kew. ISBN 978-1-84246-422-9. <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Beentje (2010), p. 109. - Beentje, Henk (2010). The Kew Plant Glossary. Richmond, Surrey: Royal Botanic Gardens, Kew. ISBN 978-1-84246-422-9. <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Beentje (2010), p. 109. - Beentje, Henk (2010). The Kew Plant Glossary. Richmond, Surrey: Royal Botanic Gardens, Kew. ISBN 978-1-84246-422-9. <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Beentje (2010), p. 109. - Beentje, Henk (2010). The Kew Plant Glossary. Richmond, Surrey: Royal Botanic Gardens, Kew. ISBN 978-1-84246-422-9. <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Beentje (2010), p. 39. - Beentje, Henk (2010). The Kew Plant Glossary. Richmond, Surrey: Royal Botanic Gardens, Kew. ISBN 978-1-84246-422-9. <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Beentje (2010), p. 71. - Beentje, Henk (2010). The Kew Plant Glossary. Richmond, Surrey: Royal Botanic Gardens, Kew. ISBN 978-1-84246-422-9. <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Bold, Alexopoulos & Delevoryas (1987), p. 322. - Bold, Harold C.; Alexopoulos, Constantine J. & Delevoryas, Theodore (1987). Morphology of Plants and Fungi (5th ed.). New York: Harper & Row. ISBN 0-06-040839-1. <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Bold, Alexopoulos & Delevoryas (1987), p. 322. - Bold, Harold C.; Alexopoulos, Constantine J. & Delevoryas, Theodore (1987). Morphology of Plants and Fungi (5th ed.). New York: Harper & Row. ISBN 0-06-040839-1. <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Gifford & Foster (1988), p. 45. - Gifford, Ernest M. & Foster, Adriance S. (1988). Morphology and Evolution of Vascular Plants (3rd ed.). New York: W. H. Freeman and Company. ISBN 0-7167-1946-0. <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> </ol>