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Abstract Detail


Paleobotanical Section

Matsunaga, Kelly K.S. [1], Stockey, Ruth [2], Tomescu, Alexandru [1].

A chlorolichen with modern thallus organization from the Early Cretaceous (Valanginian-Hauterivian) of Vancouver Island (British Columbia, Canada).

Mutualistic association with photosynthetic autotrophs, in the form of lichen symbioses, is a highly successful nutritional strategy among fungi. Today > 20% of known fungal species are lichenized, and lichens dominate 8% of terrestrial ecosystems. Despite the diversity of extant lichens, their fossil record is spotty and unequivocal lichen fossils are rare. Here we present a new lichen from Early Cretaceous deposits (Valanginian-Hauterivian boundary, ca. 136 Ma) at the Apple Bay locality, on Vancouver Island (British Columbia). The specimen is a thallus fragment of a foliose or squamulose lichen 260 µm thick, 1.1 mm wide, and at least 1.3 mm long. The lichen exhibits the complex internal stratification of a modern heteromerous lichen, consisting of an upper and lower cortex, medulla, and photobiont layer. Both upper and lower cortex are comprised of a dense reticulum of anastomosing hyphae 1.1-3.5 µm in diameter. Each is differentiated into a thinner outer layer with a denser reticulum, and an inner layer with looser structure. The medulla consists of hyphae 1-2.5 µm in diameter that run parallel to the cortex. Transverse septations devoid of clamp connections were observed in cortical and medullary hyphae, indicating that the mycobiont is an ascomycete. The photobiont layer consists of globose cells 5.8-11.6 µm in diameter surrounded by mycobiont hyphae. Characters of the photobiont cells including size, contents, and grouping, in conjunction with the type of mycobiont-photobiontinterface, indicate that the photobiont of this lichen is a chlorophyte. The mycobiont-photobiont interface is exceptionally well-preserved. It consists of thin branching hyphae and irregular hyphal appressions that encase and connect algal cells. Intracellular haustoria occur frequently throughout the specimen in both healthy and degraded cells. The Apple Bay lichen provides the earliest evidence of thalli with modern stratified organization and is the oldest lichen containing a chlorophyte photobiont. Furthermore, this lichen yielded the only fossilized evidence of a complex mycobiont-photobiont interface characterized by wall appressions and intracellular haustoria. The structure and organization of the Apple Bay lichen indicates that anatomically complex heteromerous thalli formed by ascomycetes and green algae had evolved by the Cretaceous.

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1 - Humboldt State University, Department of Biological Sciences, 1 Harpst Street, Arcata, CA, 95521, USA
2 - Oregon State University, Department of Botany and Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331, USA

Keywords:
Cretaceous
lichen
fossil
Chlorophyta
Ascomycota
mycobiont
photobiont.

Presentation Type: Oral Paper:Papers for Sections
Session: 9
Location: Union A/Hyatt
Date: Monday, July 9th, 2012
Time: 11:15 AM
Number: 9004
Abstract ID:597


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