Department of Botany and Plant Pathology, Cordley Hall, Oregon State University, Corvallis, OR, 97331, USA.
Department of Environmental and Plant Biology, Ohio University, Athens, OH, 45701, USA.
Am J Bot. 2023 Aug;110(8):e16210. doi: 10.1002/ajb2.16210. Epub 2023 Aug 3.
An anatomically preserved fossil fern sporeling has been discovered in a Lower Cretaceous marine concretion from Vancouver Island, British Columbia, Canada, providing an opportunity to characterize rhizome growth from an extinct species.
The specimen was studied from serial transverse sections prepared by the cellulose acetate peel technique.
The rhizome ranges from ~0.7 to 1.1 mm in diameter, has a sclerenchymatous pith, a stele that attains a dictyoxylic architecture, and sclerenchymatous outer cortex, features that are characteristic of osmundaceous rhizomes. Cauline xylem forms a medullated protostele or solenostele at some levels, but is dissected into discrete xylem bundles at others. Fronds diverge in a helical phyllotaxis, range up to 1.1 mm in greatest dimension, and have a C-shaped trace and outer cortex of sclerotic cells. Inside the sclerenchyma of the petioles are two lateral sclerotic strands and a sclerotic bundle adaxial to the trace. Together, these characters reveal the occurrence of a new species, Todea minutacaulis and provide evidence for developmental changes that occur in the rhizome as the sporeling increased in size.
Small size of the specimen, medullated protostelic-dictyoxylic solenostelar vascular architecture, and incompletely sclerified cells apically reveal that osmundaceous sporeling development has remained constant since at least the Early Cretaceous. Together with Todea tidwellii and Osmunda vancouverensis that also are present in the Apple Bay flora, this sporeling documents the occurrence of a multispecies assemblage of osmundaceous ferns and demonstrates that the genus Todea was diversifying rapidly by the Early Cretaceous.
在加拿大不列颠哥伦比亚省温哥华岛的下白垩纪海相结核中发现了一株保存完好的解剖化石蕨类孢子体，为研究灭绝物种的根茎生长提供了机会。
通过纤维素醋酸酯皮技术制备的连续横切面对标本进行了研究。
根茎直径约为 0.7 至 1.1 毫米，具有韧皮部髓，一个达到二原型结构的中柱，以及韧皮部外皮层，这些特征是 osmundaceae 根茎的特征。在某些水平上，茎木质部形成有髓原中柱或分体中柱，但在其他水平上则被分割成离散的木质部束。叶片以螺旋状叶序展开，最大尺寸可达 1.1 毫米，具有 C 形痕迹和硬化细胞的外皮层。叶柄的韧皮部内有两条侧硬化束和一条靠近痕迹的硬化束。这些特征共同揭示了一种新物种 Todea minutacaulis 的存在，并为在孢子体生长过程中发生的根茎发育变化提供了证据。
标本体积小、髓原二原型-二歧分叉中柱的维管束结构以及顶部未完全硬化的细胞表明，osmundaceae 孢子体的发育自至少早白垩纪以来一直保持不变。与也存在于 Apple Bay 植物群中的 Todea tidwellii 和 Osmunda vancouverensis 一起，这个孢子体记录了 osmundaceae 蕨类植物的多种物种组合的发生，并表明 Todea 属在早白垩纪就已经迅速多样化。
