An Early Devonian actinostelic euphyllophyte with secondary growth from the Emsian of Gaspé (Canada) and the importance of tracheid wall thickening patterns in early euphyllophyte systematics

Secondary growth is a tracheophyte structural feature whose earliest known occurrence dates to the late Pragian-early Emsian.  Armoricaphyton, Franhueberia and an unnamed plant from eastern Canada represent the only instances of secondary growth documented to date for the Early Devonian.  Here, we describe a new Early Devonian euphyllophyte exhibiting secondary growth, from the Emsian (c. 400-395 Ma) Battery Point Formation (Québec, Canada): Gmujij tetraxylopteroides gen. et sp. nov. is characterized by a mesarch actinostele with Psilophyton-type (P-type) tracheid wall thickenings and exhibits a new type of anatomical organization among Early Devonian wood-producing euphyllophytes.  Gmujij differs from coeval euphyllophytes, but lack of data on branching patterns, reproductive structures and other traditional diagnostic features preclude classification among previously recognized euphyllophyte groups.  We experiment with a numerical approach to tracheid size distributions, to compare Gm...

次生生长（secondary growth）是维管植物（tracheophyte）的结构特征，目前已知其最早出现于晚布拉格期（Pragian）-早埃姆斯期（Emsian）。Armoricaphyton、Franhueberia以及一种发现于加拿大东部的未命名植物，是迄今早泥盆世（Early Devonian）仅有的已被记录的具次生生长的类群。本文报道产自加拿大魁北克省（Québec）埃姆斯阶（Emsian，约400~395 Ma）巴特里角组（Battery Point Formation）的一件早泥盆世真叶植物（euphyllophyte）新类群，其展现出次生生长特征，命名为Gmujij tetraxylopteroides gen. et sp. nov.（新属新种）：该类群具有以裸蕨型（Psilophyton-type，简称P型）管胞（tracheid）壁加厚为特征的中始式星状中柱（mesarch actinostele），在早泥盆世产木质部真叶植物中展现出一种全新的解剖组织结构。Gmujij与同时代的真叶植物存在差异，但由于缺乏分枝模式（branching patterns）、生殖结构（reproductive structures）及其他传统鉴别特征（diagnostic features）的相关数据，目前无法将其归入已被公认的真叶植物类群。我们尝试采用数值方法（numerical approach）分析管胞大小分布，以对比Gm……