Department of Biological Sciences, California State Polytechnic University-Humboldt, Arcata, CA 95521, USA.
Botany Department, Trinity College, Dublin, 2, Ireland.
Am J Bot. 2024 Oct;111(10):e16418. doi: 10.1002/ajb2.16418. Epub 2024 Oct 13.
Cladoxylopsids, one of the first lineages with complex organization to rise from the plexus of structurally simple plants that comprised the earliest euphyllophyte floras, are moniliformopsid euphyllophytes. They formed Earth's earliest forests by the Middle Devonian and are thought to have given rise to the equisetopsids and probably some fern lineages. The Lower Devonian (Emsian) Battery Point Formation (Quebec, Canada) contains previously unrecognized cladoxylopsids preserved anatomically. One of these provides new data on structural evolution among euphyllophytes and is described here.
The anatomy and morphology of permineralized axes of the new plant were studied with light and electron microscopy on sections produced using the cellulose acetate peel technique. Morphological comparisons and phylogenetic analysis were used for taxonomic placement of the plant.
The plant represents a new species, Paracladoxylon kespekianum Chu et Tomescu, gen. et sp. nov., that has tracheids with modern-looking bordered pits and the complex cauline vascular architecture characteristic of the genus Cladoxylon. Its dissected ultimate appendages have complex regular taxis and a pattern of vascularization that suggests bilateral symmetry.
Paracladoxylon kespekianum is one of the largest Early Devonian euphyllophytes, among the oldest representatives of the cladoxylopsid group, and older than any species of the closely related Cladoxylon by at least 35 million years. It is also one of the oldest anatomically preserved representatives of the cladoxylopsid group. Its anatomical organization pushes the rise of complex vascular architecture among moniliformopsid euphyllophytes deeper in time than previously recognized.
cladoxylopsids 是最早的复杂组织谱系之一，从构成最早的真叶植物花系的结构简单植物丛中崛起，是 moniliformopsid 真叶植物。它们在中泥盆世形成了地球最早的森林，被认为是节蕨类植物和可能的一些蕨类植物谱系的起源。下泥盆统（埃姆斯期）电池点组（加拿大魁北克）含有以前未被识别的 cladoxylopsids，其保存了解剖学特征。其中之一为真叶植物的结构演化提供了新的数据，并在此进行描述。
使用纤维素醋酸酯皮技术制作切片，通过光镜和电子显微镜研究新植物的矿化轴的解剖结构和形态。进行形态比较和系统发育分析，以确定该植物的分类位置。
该植物代表了一个新种，Paracladoxylon kespekianum Chu et Tomescu，gen. et sp. nov.，它具有具有现代外观的具缘纹孔的管胞，以及典型 cladoxylon 属的复杂茎干维管束结构。其解剖的最终附属物具有复杂的规则排列和血管化模式，表明具有双侧对称性。
Paracladoxylon kespekianum 是最早的泥盆纪真叶植物之一，是 cladoxylopsid 群中最古老的代表之一，比密切相关的 Cladoxylon 属的任何物种都要早至少 3500 万年。它也是 cladoxylopsid 群中最早保存解剖结构的代表之一。其解剖组织的复杂性将复杂的维管束结构在 moniliformopsid 真叶植物中的出现时间推得比以前认为的更早。
