Department of Botany, University of British Columbia , Vancouver BC, V6T 1Z4, Canada.
Department of Botany and Plant Pathology, 2082 Cordley Hall, Oregon State University, Corvallis, Oregon 97331.
Mycologia. 2020 May-Jun;112(3):504-518. doi: 10.1080/00275514.2020.1718441. Epub 2020 Mar 13.
Fly-speck fungi reproduce via thyriothecia that consist of sporogenous tissue appressed to cuticle surfaces of plant leaves and covered by a shield-like scutellum. Thyriothecial scutella likely evolved repeatedly in Dothideomycetes (Ascomycota), and their morphology varies by lineage. Fly-speck fungi have an exceptionally good fossil record that begins in the Mesozoic. The interpretation of scutellum characters in fossils may provide insights into origins of Dothideomycetes and help calibrate the timing of ascomycete evolution. From sediments of the Lower Cretaceous (125-112 Ma) Potomac Group of Virginia, from Dutch Gap Canal, lower Zone 1, we found scutella similar to those of extant Aulographaceae (Dothideomycetes), attached to a single piece of dispersed coniferous cuticle. We analyze hyphae and scutellum development among four extant Aulographaceae species for comparison with the fossil. The excellent preservation of fungi on the leaf cuticle surface allows us to infer a developmental sequence for the fossil. Scutellum development begins with coordinated growth of multiple neighboring generator hyphae and continues with hyphae producing two-dimensional pseudomonopodial, dichotomous, radial growth. Asci and ascospores were not found. We coded states for seven morphological characters using direct observations of the fossil and eight extant taxa, and using the literature for 28 others. We inferred a phylogeny using nuclear 18S and 28S rDNA of 36 extant taxa, 34 Dothideomycetes and two Arthoniomycetes. The phylogeny includes newly determined sequences from five species, two from Aulographaceae. With a branch-and-bound search, we inferred the most parsimonious placements of the fossil given the molecular tree topology. The parsimony analysis constrained by the rDNA phylogeny places the fossil taxon among stem lineages near Aulographaceae or among the known living members of Aulographaceae. We describe the fossil morphotype as , gen. et sp. nov. The fossil provides the oldest evidence of morphological characters restricted among extant fungi to Aulographaceae.
飞斑菌通过子囊壳繁殖，子囊壳由贴附在植物叶片表皮上的产孢组织和一个盾状的盾片组成。子囊壳的盾片可能在散囊菌纲（子囊菌门）中反复进化，其形态因谱系而异。飞斑菌具有非常好的化石记录，始于中生代。对化石中盾片特征的解释可能有助于了解散囊菌纲的起源，并有助于校准子囊菌进化的时间。我们在弗吉尼亚州下白垩统（125-112 百万年前）波托马克组的荷兰峡谷运河下部 1 区发现了与现存的节皮菌科（散囊菌纲）相似的盾片，这些盾片附着在一块分散的针叶状表皮上。我们分析了四个现存的节皮菌科物种的菌丝和盾片发育情况，以便与化石进行比较。真菌在叶片表皮上的良好保存使我们能够推断出化石的发育序列。盾片的发育始于多个相邻发生器菌丝的协调生长，并继续由产生二维单轴、二叉、放射状生长的菌丝进行。没有发现子囊和子囊孢子。我们使用化石的直接观察和 8 个现存分类群对 7 个形态特征进行了编码，并使用文献对另外 28 个特征进行了编码。我们使用来自 36 个现存分类群、34 个散囊菌纲和 2 个节皮菌纲的核 18S 和 28S rDNA 推断了系统发育。系统发育树包括从五个物种中确定的新序列，其中两个来自节皮菌科。通过分支和界限搜索，我们根据分子树拓扑推断了化石在最简约位置的位置。由 rDNA 系统发育约束的简约分析将化石分类群置于与节皮菌科或已知的节皮菌科活成员接近的茎系中。我们将化石形态型描述为 ，属和种。新。化石提供了最早的证据，证明了形态特征仅限于现存真菌中的节皮菌科。
