Protographum luttrellii Le Renard, Upchurch, Stockey & Berbee, sp. nov. FIG. 1
MycoBank number: MB 831508; Index Fungorum number: IF 831508; Facesoffungi number: FoF 12432;
Typification: USA. VIRGINIA: Potomac Group, lower Zone 1, Pseudofrenelopsis parceramosa bed; Aptian (Lower Cretaceous, 125–113 Ma). Holotype specimen occurring in slide DG 083 fragment B (England Finder coordinates M43–O43, label on specimen slide to the right), deposited in the Denver Museum of Nature and Science under slide EPI.53110.
Etymology: The species is named in honor of the late Everett S. Luttrell, University of Georgia, for his contributions to the study of Aulographaceae and other thyriothecial Dothideomycetes.
Diagnosis: Superficial mycelium composed of septate hyphae, 1–3 µm wide; appressoria infrequent. Thyriothecia represented by shield-like scutella appressed to host leaf surface, circular to elongate in largest specimens. Young scutella 20–60 µm diam, connected to surrounding mycelium by multiple generator hyphae; made of pseudomonopodial dichotomously branching hyphae, 1–3 µm wide, radiating from generator hyphae and overlapping with one another, mostly nonseptate; few cross-septa laid in older, proximal portion of hyphae.
Notes: Protographum luttrellii is distinguished from other fossil taxa by pseudomonopodial dichotomous branching in a scutellum initiated by multiple generator hyphae (Table 1). Due to its lack of asci and ascospores and of a known mode of dehiscence (ostiole vs. slit), the fossil cannot be placed in a living genus.
Table 1. Comparison of Protographum luttrelli characters with fossils discussed in text.
Figure 1. Fossils of Protographum luttrellii, gen. et sp. nov., on Lower Cretaceous (125–112 Ma) cuticle of unidentified conifer. Holotype, DMNS EPI.53110. A. Overview of cuticle with P. luttrellii (black arrowheads), and an undescribed species arising from the stomata that are aligned in rows (white arrowheads); pollen grain (P). B. Closer view of two P. luttrellii scutella (black arrowheads), one on old sporocarp (white arrowheads) of a fungal colonizer of stomata (S). C. Higher magnification of box from A; a large thyriothecium with some morphological similarities to P. luttrellii connected to surrounding mycelium in at least three points (black arrowheads); growing next to a row of stomata colonized by a different fungus (white arrowheads). Possible, faint line of dehiscence (white arrows). D–F. Young thyriothecia of P. luttrellii initiated from at least three surface hyphae (black arrowheads). G. Close-up of dashed box from C; pseudomonopodial dichotomous branching less obvious than in smaller scutella; septation and overlap between neighboring hyphae obscures evidence of early hyphal branching. H–J. Higher magnification of boxes from D–F, respectively, showing pseudomonopodial dichotomous branching; septa restricted to proximal segments of hyphae (black arrowheads). K. Higher magnification of box from G, showing hyphal segments that may have originated through septation of pseudomonopodial dichotomies (white arrowheads). Elongate hyphal segments distal to septa (black arrowhead) are unbranched. L, M. Intercalary appressoria with penetration pegs (white arrowheads). L. Appressorium connected to large sporocarp in C. M. Appressorium connected to hypha of smaller sporocarp. Illustration of manually assembled stacks of three and two focal planes in D and E, respectively. All other illustrations are of a single focal plane. Bars: A = 50 µm; B–C = 20 µm; D–G = 10 µm; H–M = 2 µm.