Reinvestigation of the Enigmatic Carboniferous Sphenophyte Strobilus Cheirostrobus Scott and Implications of In Situ Retusotriletes Spores
Reinvestigation of the Enigmatic Carboniferous Sphenophyte Strobilus Cheirostrobus Scott and Implications of In Situ Retusotriletes Spores
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神秘的石炭纪蝶藻 Strobilus Cheirostrobus Scott 的重新研究及其原位 Retusotriletes 孢子的意义
DOI：
10.1086/704945
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发表时间：
2019
影响因子：
2.3
通讯作者：
Neregato R
中科院分区：
文献类型：
--
作者：
Neregato R
Cheirostrobus pettycurensisScott是石炭纪早期的一种蝶形植物，仅从其解剖学上保存的孢子叶中了解到，孢子叶具有高度解剖的“孢子叶”，包括下部营养部分和上部可育部分，孢子囊向内。自100多年前斯科特的开创性工作以来，该属一直没有被重新调查，因此它仍然缺乏特征，其系统位置也是谜。我们重新调查了Cheirostrobus，提供了新的见解，其结构，解剖学，并在原位孢子，从而解决长期存在的问题，其相当大的系统和进化的重要性。方法：历史上准备的幻灯片Cheirostrobus从博物馆藏品进行了检查，以方便详细的描述，使用现代术语，允许更有效的比较和解释。 原生木质部有圆形和后生木质部梯状纹孔。主维管束以重叠轮状从中柱分离，在皮层附近垂直分裂，下部（背轴）子束提供2或3个苞片，上部（正轴）子束提供2或3个孢子囊柄，每个苞片对着一个孢子囊柄。单个的孢子囊梗有一个叶尖，通常有四个向内的、纵向伸长的孢子囊，排列成两个垂直的行。原位孢子为同孢子，三裂，边缘突出，外壁脱落，直径为48至77 μm。孢子形态与散孢囊菌（Thesporae dispersae）一致。它被解释为楔叶目的一个成员，在进化的茎谱系上，导致地层上更年轻的炉甘石科。Retusotriletes型孢子首次在楔叶植物中原位报道，以前曾在喙叶植物中发现，在分散的记录中，Retusotriletes incohatus的范围从晚法门期开始，（泥盆纪）至晚期维塞安（石炭纪），常见于基底石炭纪沉积，这表明Cheirostrobus（或产生同种孢子的密切相关的植物）的地层范围比以前认识的要长，并且是石炭纪最早的顶点。
Premise of research.Cheirostrobus pettycurensisScott is an early Carboniferous sphenophyte known only from its anatomically preserved strobili, which bear highly dissected “sporophylls” comprising a lower vegetative part and an upper fertile part bearing inwardly facing sporangia. Since Scott’s pioneering work over 100 years ago, the genus has not been reinvestigated such that it remains poorly characterized and its systematic position enigmatic. We reinvestigateCheirostrobus, providing new insights into its structure, anatomy, and in situ spores and thereby addressing long-standing questions concerning its considerable systematic and evolutionary importance.Methodology. Historically prepared slides ofCheirostrobusfrom museum collections were examined using transmitted light microscopy to facilitate a detailed description using modern terminology, allowing for more effective comparisons and interpretations.Pivotal results. The strobilus axis comprises a stellate protostele with 9–13 protoxylem poles showing exarch maturation. The protoxylem has circular and metaxylem scalariform pitting. The main vascular bundles depart from the stele in superposed whorls and divide vertically close to the cortex, from which the lower (abaxial) daughter bundle supplies two or three bracts and the upper (adaxial) daughter bundle supplies two or three sporangiophores, with each bract subtending one sporangiophore. Individual sporangiophores have a foliar apex and typically bear four inwardly facing, longitudinally elongated sporangia disposed in two vertical rows. In situ spores are homosporous and trilete, have a prominent margo with leavigate exine, and range from 48 to 77 μm in diameter. Spores conform to thesporae dispersae Retusotriletes incohatusSullivan 1964.Conclusions.Cheirostrobushas an organization similar to members of the Sphenophyllales and the Calamitales; it is interpreted as a member of the Sphenophyllales that is on the evolutionary stem lineage leading to the stratigraphically younger Calamitaceae.Retusotriletes-type spores are reported in situ for the first time within sphenophytes, having previously been found within rhyniophytes, zosterophylls, trimerophytes, and algae, further emphasizing the polyphletic nature of the genus and convergent spore evolution across multiple lineages.Retusotriletes incohatusin the dispersed record ranges from the late Famennian (Devonian) to the late Viséan (Carboniferous) and is common in basal Carboniferous deposits, suggesting thatCheirostrobus(or closely related plants producing the same kind of spores) had a longer stratigraphic range than was previously recognized and an earliest Carboniferous acme.