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Junggaria
''Junggaria'' was a genus of rhyniophyte-like land plants known from fossils found in China in Upper Silurian strata (, around ). It bore leafless dichotomously or pseudomonopodially branching axes, some of which ended in spore-forming organs or sporangia of complex shape. The genus ''Cooksonella'', found in Khazakstan from deposits of a similar age, is considered to be an illegitimate synonym.〔
==Description==
''Junggaria spinosa'' was first described as a new species by Dou in 1983,〔 from four fossil specimens found in the Wutubulake Formation, Xinjiang, China, now dated to the Late Silurian (, around ). Further specimens were found later and a more detailed description was published in 1993 by Cai et al.〔
The specimens are fragmentary so that a full reconstruction is difficult. It appears that the sporophyte of ''Junggaria spinosa'' had 'pseudomonopodial' branching, i.e. the leafless stems (axes) divided into two branches in such a way that one continued as the 'main' stem and the other became a side or lateral branch. Lateral branches divided dichotomously up to twice, terminating in spore-forming organs or sporangia. Stems varied in width from around 1.1 mm to 2.5 mm. Most of the stems were smooth but some bore hair-like structures up to 0.1 mm in diameter and 0.5 mm long. A darker central strand was observed on some stems, but the internal structure is not known.〔
In the flattened fossils, the sporangia consist of a central, roughly circular area, on average 2 mm in diameter, smoothly connected to the end of the stem on which they were borne. Around the top and sides of the central area there is a border, around 1 mm wide, which is not connected to the stem and ends abruptly. The border varies in shape, sometimes being uniform, sometimes lobed; it appears to consist of two layers separated by a 'filling'. The layers appear separated into two 'valves' in some specimens. Cai et al. say that it is difficult to reconstruct the three-dimensional structure of a sporangium before preservation; it may have been more-or-less spherical or it may already have been compressed from side to side before being fossilized. They concluded that "()hese unique and somewhat bizarre sporangia ... defy our understanding", but that the most surprising feature was their complexity relative to other Silurian species such as ''Salopella'', ''Cooksonia'' or ''Steganotheca''.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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