rhyniophytes A group of extinct vascular land plants that flourished in the early Devonian (400–380 million years ago). They had short upright aerial axes (‘stems’), several centimetres tall, that arose from rhizomes or corms and branched dichotomously to form two equal growing points. The ‘naked’ branches lacked leaves and ended in multicellular spore-forming organs (sporangia). Rhyniophytes, such as Cooksonia and Rhynia (named after fossil-rich chert deposits at Rhynie in Scotland), were the earliest true vascular plants, having a solid mass of xylem vessels in the centre of the stem. In the 1980s, evidence emerged of the coexistence of similar gametophyte forms alongside the sporophyte rhyniophytes. This prompted speculation that these might have been alternative forms of the same species and that subsequent reduction of the gametophytes could have led to evolution of the predominant sporophyte forms of modern vascular plants (see transformation hypothesis). Compare trimerophytes; zosterophyllophytes.
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