Parmotrema specimen 1

Specimen.

Stuttgart State Museum of Natural History, Germany (SMNS), SMNS -DO-4928-M; syninclusion unidentified leafy liverwort of the order Porellales.

Age and stratigraphic level.

15‒20 Ma, Langhian – Burdigalian (early to middle Miocene), La Toca Formation, Dominican Republic.

Description.

Lichen fragment approximately 5.4 × 2.6 mm in diameter. Thallus foliose, lobate. Lobes robust, flat, and linear, 0.4–0.9 mm wide, lobe apices truncate (Fig. 7 B). Upper surface slightly uneven, brown, with prominent dark margins (Fig. 7 C). Medulla not visible. Lower cortex dark. Marginal cilia long (up to at least 0.8 mm), dark, thick and tapered (Fig. 7 B, C). Rhizines dark, shorter than cilia. Isidia abundant, laminal, finger-shaped, up to 150 µm long (Fig. 7 C). Apothecia, soredia, or pycnidia not present.

Discussion.

The general habit and long, thick, and tapered marginal cilia identify the specimen as Parmotrema. Parmotrema is an extant genus with approximately 300 species mainly distributed in tropical and subtropical regions, especially in the Pacific Islands and South America (Thell et al. 2012). It is part of the parmelioid crown group of the Parmeliaceae (Pizarro et al. 2018) where apothecial and conidial characters, growth form, cortical and medullar chemistry, and presence, absence and / or type of cell-wall polysaccharides, marginal cilia, rhizines, and surface features, like epicortex and pseudocyphellae, have been used to separate genera (Crespo et al. 2011). Like in many parmelioid genera, molecular phylogenetics have repeatedly shaped the generic boundaries of Parmotrema (e. g., Blanco et al. 2005; Divakar et al. 2005, 2017; Crespo et al. 2011). As the species level taxonomy of Parmotrema mainly relies on chemical and other characters not observable in the fossil inclusions, comparisons of fossils to extant species are often ineffectual. However, the genus currently includes several infrageneric groups that, at some point, have been acknowledged as separate genera based on morphology, anatomy, and chemistry but which were found to be nested within Parmotrema in molecular phylogenetic analyses (Elix 1993; Blanco et al. 2005; Divakar et al. 2005, 2017; Crespo et al. 2011). Parmotrema specimen 1 with the smooth upper surface, dark lower surface, and very long, branched marginal cilia resembles the Parmotrema s. str. group within the genus Parmotrema. The group is, for example, characterized by broad lobes, broad naked marginal zone on the lower surface, marginal cilia, and the lack of maculae on the upper surface (Elix 1993). The extant Parmotrema s. str. group contains more than 250 species distributed especially in the tropical regions of the world (Elix 1993).