Data from: The fossil Osmundales (Royal Ferns)—a phylogenetic network analysis, revised taxonomy, and evolutionary classification of anatomically preserved trunks and rhizomes

The Osmundales (Royal Fern order) originated in the late Paleozoic and is the most ancient surviving lineage of leptosporangiate ferns. In contrast to its low diversity today (less than 20 species in six genera), it has the richest fossil record of any extant group of ferns. The structurally preserved trunks and rhizomes alone are referable to more than 100 fossil species that are classified in up to 20 genera, four subfamilies, and two families. This diverse fossil record constitutes an exceptional source of information on the evolutionary history of the group from the Permian to the present. However, inconsistent terminology, varying formats of description, and the general lack of a uniform taxonomic concept renders this wealth of information poorly accessible. To this end, we provide a comprehensive review of the diversity of structural features of osmundalean axes under a standardized, descriptive terminology. A novel morphological character matrix with 45 anatomical characters scored for 15 extant species and for 114 fossil operational units (species or specimens) is analysed using networks in order to establish systematic relationships among fossil and extant Osmundales rooted in axis anatomy. The results lead us to propose an evolutionary classification for fossil Osmundales and a revised, standardized taxonomy for all taxa down to the rank of (sub)genus. We introduce several nomenclatural novelties: (1) a new subfamily Itopsidemoideae (Guaireaceae) is established to contain Itopsidema, Donwelliacaulis, and Tiania; (2) the thamnopteroid genera Zalesskya, Iegosigopteris, and Petcheropteris are all considered synonymous with Thamnopteris; (3) 12 species of Millerocaulis and Ashicaulis are assigned to modern genera (tribe Osmundeae); (4) the hitherto enigmatic Aurealcaulis is identified as an extinct subgenus of Plenasium; and (5) the poorly known Osmundites tuhajkulensis is assigned to Millerocaulis. In addition, we consider Millerocaulis stipabonettiorum a possible member of Palaeosmunda and Millerocaulis estipularis as probably constituting the earliest representative of the (Todea-)Leptopteris lineage (subtribe Todeinae) of modern Osmundoideae.

紫萁目（Osmundales，皇蕨目）起源于晚古生代，是现存最古老的薄囊蕨类（leptosporangiate ferns）谱系。相较于如今极低的多样性（6个属仅含不足20个物种），该类群拥有所有现存蕨类类群中最为丰富的化石记录。仅结构保存完好的茎干与根状茎，就可归入超过100个化石物种，这些化石被划分为多达20个属、4个亚科以及2个科。这一多样的化石记录，是该类群从二叠纪至今的演化历史的绝佳信息来源。然而，术语使用不统一、描述格式各异，且普遍缺乏统一的分类学概念，使得这一丰富的信息难以被高效获取与利用。为此，我们基于标准化的描述术语，全面综述了紫萁目轴结构的多样性特征。我们构建了包含45个解剖学性状的新型形态性状矩阵，对15个现存物种以及114个化石操作分类单元（operational units，物种或标本）开展网络分析，以建立基于轴解剖结构的紫萁目化石类群与现存类群间的系统发育关系。研究结果促使我们提出了紫萁目化石类群的演化分类方案，并对所有至（亚）属级别的类群修订了标准化的分类系统。我们引入了多项分类学新处理：（1）建立新亚科Itopsidemoideae（隶属于Guaireaceae科），以容纳Itopsidema、Donwelliacaulis和Tiania三个属；（2）将穗蕨类（thamnopteroid）类群的Zalesskya、Iegosigopteris及Petcheropteris均归为Thamnopteris的同物异名；（3）将12个Millerocaulis和Ashicaulis属的物种归入现代紫萁族（Osmundeae）的属中；（4）将此前分类地位不明的Aurealcaulis鉴定为Plenasium的一个已灭绝亚属；（5）将研究较少的Osmundites tuhajkulensis归入Millerocaulis属。此外，我们认为Millerocaulis stipabonettiorum可能属于Palaeosmunda属，而Millerocaulis estipularis大概率是现代Osmundoideae亚科下（Todea-）Leptopteris谱系（Todeinae亚族）的最早代表类群。