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，俗称皇家蕨类）起源于晚古生代，是现存最古老的薄囊蕨类（leptosporangiate ferns）演化支。相较于现今极低的物种多样性（6属不足20种），它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化石，就可归属于超过100个化石物种，这些化石被划分为至多20个属、4个亚科以及2个科。这一多样的化石记录，为该类群自二叠纪至今的演化历史提供了极为珍贵的研究资料。然而，由于术语使用不统一、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资源难以被有效获取与利用。为此，我们采用标准化描述术语，对紫萁目轴部结构的特征多样性开展了全面综述。本研究构建了一套包含45个解剖学特征的全新形态特征矩阵，针对15个现存物种与114个化石操作分类单元（物种或标本）进行特征编码，并通过网络分析法展开研究，以期基于轴部解剖结构厘清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针对化石紫萁目的演化分类方案，并建立了针对直至（亚）属级别的所有类群的修订版标准化分类体系。我们还提出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与Tiania三个属；（2）将Thamnopteris类群的Zalesskya、Iegosigopteris及Petcheropteris均视为Thamnopteris的同物异名；（3）将12个隶属于Millerocaulis与Ashicaulis的物种归入现代紫萁族（Osmundeae）的属中；（4）此前归属存疑的Aurealcaulis被鉴定为Plenasium的已灭绝亚属；（5）研究程度较低的Osmundites tuhajkulensis被归入Millerocaulis属。此外，我们认为Millerocaulis stipabonettiorum可能属于Palaeosmunda属，而Millerocaulis estipularis或许是现代紫萁亚科（Osmundoideae）的（Todea-)Leptopteris演化支（托德蕨亚族Todeinae）最早的代表类群。