Spore bearing plants examples with names10/4/2023 A variety of names have been used, which the table below summarizes.Īlternative names for Banks' three groups of early polysporangiophytesįor Banks, rhyniophytes comprised simple leafless plants with terminal sporangia (e.g., Cooksonia, Rhynia) with centrarch xylem zosterophylls comprised plants with lateral sporangia that split distally (away from their attachment) to release their spores, and had exarch strands of xylem (e.g., Gosslingia). These groups have since been treated at the ranks of division, class and order. In 1975, Banks expanded on his earlier 1968 proposal that split it into three groups at the rank of subdivision. Īs additional fossils were discovered and described, it became apparent that the Psilophyta were not a homogeneous group of plants. The living Psilotaceae, the whisk-ferns, were sometimes added to the class, which was then usually called Psilopsida. Prior to that, most of the early polysporangiophytes had been placed in a single order, Psilophytales, in the class Psilophyta, established in 1917 by Kidston and Lang. Polysporangiophytes may or may not have vascular tissue – those that do are vascular plants or tracheophytes. This distinguishes polysporangiophytes from liverworts, mosses and hornworts, which have unbranched sporophytes each with a single sporangium. (The taxobox at the right represents their view of the classification of the polysporangiophytes.) The defining feature of the clade is that the sporophyte branches and bears multiple sporangia. The concept of the polysporangiophytes, more formally called Polysporangiophyta, was first published in 1997 by Kenrick and Crane. Fossils assigned to the genus Cooksonia, which is more certainly a polysporangiophyte, have been dated to the succeeding Wenlock epoch ( 433 to 427 million years ago). Īs of 2019, Eohostimella, dated to the Llandovery epoch ( 444 to 433 million years ago), is one of the earliest fossils that has been identified as a polysporangiophyte. Since these discoveries, similar megafossils have been discovered in rocks of Silurian to mid-Devonian age throughout the world, including Arctic Canada, the eastern USA, Wales, the Rhineland of Germany, Kazakhstan, Xinjiang and Yunnan in China, and Australia. The vertical stems were dichotomously branched with some branches ending in sporangia. The fossils were better-preserved than Dawson's, and showed clearly that these early land plants did indeed consist of generally naked vertical stems arising from similar horizontal structures. Lang published a series of papers describing fossil plants from the Rhynie chert – a fine-grained sedimentary rock found near the village of Rhynie, Aberdeenshire, now dated to the Pragian of the Lower Devonian (around 411 to 408 million years ago). įrom 1917 onwards, Robert Kidston and William H. speculate that this was because his reconstruction looked very unusual and the fossil was older than was expected. Dawson's discoveries initially had little scientific impact Taylor et al. Cross-sections of the upright axes showed that vascular tissue was present. The upright stems or axes branch dichotomously and have pairs of spore-forming organs ( sporangia) attached to them. The reconstruction shows horizontal and upright stem-like structures no leaves or roots are present. In 1859 he published a reconstruction of a Devonian plant, collected as a fossil from the Gaspé region of Canada, which he named Psilophyton princeps. ĭawson, a Canadian geologist and paleobotanist, was the first to discover and describe a megafossil of a polysporangiophyte. Megafossils are preserved parts of plants large enough to show structure, such as stem cross-sections or branching patterns. Microfossils are primarily spores, either single or in groups. Paleobotanists distinguish between micro- and megafossils. Extinct polysporangiophytes are known that have no vascular tissue and so are not tracheophytes.Įarly polysporangiophytes History of discovery While the definition is independent of the presence of vascular tissue, all living polysporangiophytes also have vascular tissue, i.e., are vascular plants or tracheophytes. The clade includes all land plants ( embryophytes) except for the bryophytes (liverworts, mosses and hornworts) whose sporophytes are normally unbranched, even if a few exceptional cases occur. The name literally means 'many sporangia plant'. Polysporangiophytes, also called polysporangiates or formally Polysporangiophyta, are plants in which the spore-bearing generation ( sporophyte) has branching stems (axes) that bear sporangia. unclassified fossil Polysporangiophytes.non-vascular fossil Polysporangiophytes.Modern polysporangiophyte, monarch fern is a vascular plant. Reconstruction of Aglaophyton, illustrating bifurcating axes with terminal sporangia, and rhizoids.
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