Department of Botany, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada.
Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, 97331, USA.
Am J Bot. 2021 Jan;108(1):129-144. doi: 10.1002/ajb2.1602.
Fossils can reveal long-vanished characters that inform inferences about the timing and patterns of diversification of living fungi. Through analyzing well-preserved fossil scutella, shield-like covers of fungal sporocarps, we describe a new taxon of early Dothideomycetes with a combination of characters unknown among extant taxa.
Macerated clays from the Potomac Group, lower Zone 1, from the Lower Cretaceous (Aptian, 125-113 Ma) of Virginia USA yielded one gymnospermous leaf cuticle colonized by 21 sporocarps of a single fungal morphotype. We inferred a tree from nuclear ribosomal DNA of extant species, and coded morphological characters to evaluate alternative, equally parsimonious placements of the fossil in a molecular constraint tree of extant species.
Bleximothyrium ostiolatum gen. et sp. nov. has an ostiolate scutellum of radiate, dichotomizing hyphae. Unlike otherwise similar extant and fossil taxa, B. ostiolatum has tangled hyphae at its scutellum margin. Scutella of B. ostiolatum are connected to superficial mycelium, to intercalary and lateral appressoria, and to extensive subcuticular "mycélium en palmettes". The gymnospermous host has characters consistent with identity as a non-papillate ginkgophyte or cycad.
Bleximothyrium ostiolatum is the oldest known fossil fly-speck fungus that occurs on plant cuticles and has the radiate, ostiolate scutellum known only from Dothideomycetes. Its combination of characters, its scutellum margin, and mycélium en palmettes are unknown in other extant and fossil species, and Bleximothyrium ostiolatum likely represents a new group of fly-speck fungi that may now be extinct.
化石可以揭示早已消失的特征，从而为推断活真菌的多样化时间和模式提供依据。通过分析保存完好的真菌子实体的盾状盖——即化石盾片，我们描述了一个新的早期散囊菌分类群，其具有一些在现存分类群中未知的特征组合。
美国弗吉尼亚州下白垩统（阿普特阶，1.25-1.13 亿年前）波特兰海相地层 1 带下部的泥岩中，含有单一真菌形态的 21 个子实体的 21 个子实体，这些子实体定殖在一片裸子植物叶片的角质层上。我们从现存物种的核核糖体 DNA 推断出一棵树，并对形态特征进行编码，以评估化石在现存物种分子约束树上的替代、同样简约的位置。
Bleximothyrium ostiolatum gen. et sp. nov. 具有辐射状、二叉分枝的菌丝构成的有孔盖盾片。与其他类似的现存和化石分类群不同，B. ostiolatum 的盾片边缘有纠结的菌丝。B. ostiolatum 的盾片与浅表菌丝、中间和侧生附着胞以及广泛的皮下“棕榈状菌丝体”相连。该裸子植物宿主具有与非乳突状银杏或苏铁身份一致的特征。
Bleximothyrium ostiolatum 是已知最古老的在植物角质层上发生的飞蝇真菌化石，其辐射状、有孔盖盾片仅在散囊菌纲中发现。它的特征组合、盾片边缘和棕榈状菌丝体在其他现存和化石物种中都不为人知，Bleximothyrium ostiolatum 可能代表了一个现已灭绝的飞蝇真菌新类群。
