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===The rise of plants===
Transitional fossils are not only those of animals. With the increasing mapping of the [[Phylum#Land plant phyla (divisions)|divisions]] of plants at the beginning of the 20th century, the search began for the ancestor of the [[vascular plant]]s. In 1917, [[Robert Kidston]] and [[William Henry Lang]] found the remains of an extremely primitive plant in the [[Rhynie chert]] in [[Aberdeenshire]], Scotland, and named it ''[[Rhynia]]''.<ref name="Kidston1917">{{cite journal |last1=Kidston |first1=Robert |author-link1=Robert Kidston |last2=Lang |first2=William Henry |author-link2=William Henry Lang |date=27 February 1917 |title=XXIV.—On Old Red Sandstone Plants showing Structure, from the Rhynie Chert Bed, Aberdeenshire. Part I. Rhynia Gwynne-Vaughanii, Kidston and Lang |url=https://www.biodiversitylibrary.org/item/130747#page/961/mode/1up |journal=Transactions of the Royal Society of Edinburgh |volume=51 |issue=3 |pages=761–784 |doi=10.1017/S0263593300006805 |s2cid=251580286 |issn=0080-4568 |oclc=704166643 |access-date=2015-05-18 }}</ref>
The ''Rhynia'' plant was small and stick-like, with simple [[Dichotomy|dichotomously]] branching stems without leaves, each tipped by a [[sporangium]]. The simple form echoes that of the [[sporophyte]] of [[mosses]], and it has been shown that ''Rhynia'' had an [[alternation of generations]], with a corresponding [[gametophyte]] in the form of crowded tufts of diminutive stems only a few millimetres in height.<ref name="Kerpetal2004">{{cite journal |last1=Kerp |first1=Hans |last2=Trewin |first2=Nigel H. |last3=Hass |first3=Hagen |year=2003 |title=New gametophytes from the Early Devonian Rhynie chert |journal=Transactions of the Royal Society of Edinburgh: Earth Sciences |volume=94 |issue=4 |pages=411–428 |doi=10.1017/S026359330000078X |s2cid=128629425 |issn=0080-4568 }}</ref> ''Rhynia'' thus falls midway between mosses and early vascular plants like [[fern]]s and [[Lycopodiopsida|clubmoss]]es. From a carpet of moss-like gametophytes, the larger ''Rhynia'' sporophytes grew much like simple clubmosses, spreading by means of horizontal growing stems growing [[rhizoid]]s that anchored the plant to the substrate. The unusual mix of moss-like and vascular traits and the extreme structural simplicity of the plant had huge implications for botanical understanding.<ref>{{harvnb|Andrews|1967|p=32}}</ref>
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