An extinct group of plants that flourished in the mid- to late Devonian (360–350 million years ago) and contained the ancestors of modern gymnosperms (conifers and cycads). They were shrubs and trees, some up to 12 m tall, with frondlike leaves. Progymnosperms evolved a vascular cambium that was bifacial, capable of producing not only xylem on its inner face (as in the more primitive lycophytes and sphenophytes) but also phloem on its outer face. Moreover, as the cambium was pushed outwards during radial growth of the stem, the cambial cells were able to divide radially and so function indefinitely. These features permitted the growth of wider trunks, with more efficient vascular sytems and stronger wood. Also, the first true simple leaves appear among certain members of the group, such as Archaeopteris (see telome theory
). However, reproduction was by spores, not seeds.
Cite this article
Pick a style below, and copy the text for your bibliography.
Learn more about citation styles
Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).
Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.
Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:
Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.