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Abstract Detail


Paleobotanical Section

Unger, Christa [1], Ortiz, Ashley [1], Stockey, Ruth [2], Tomescu, Alexandru [3].

An anatomically preserved leucobryaceous moss from the Early Cretaceous (Valanginian-Hauterivian) of Vancouver Island, British Columbia, Canada.

Anatomically preserved plant assemblages from the Early Cretaceous (Valanginian-Hauterivian) Apple Bay locality on Vancouver Island (British Columbia), include some of the rare occurrences of permineralized fossil mosses worldwide. Seven gametophytes preserved in marine carbonate nodules exhibit a striking feature - leaves with narrow, unistratose lamina and broad costa consisting of two layers of large leucocysts enclosing a layer of thin chlorocysts in between - highly reminiscent of the extant genus Leucobryum. Gametophyte stems are up to 520 µm in diameter, with densely arranged branches (four branches are attached along a stem segment only 0.5 mm long). The stems display well differentiated epidermis and cortex consisting of isodiametric cells that become larger and thinner-walled toward the center. A thin conducting strand of small,thin-walled cells is present at the center. Leaves have decurrent bases and are densely inserted on the stem. They are 750 µm wide at the base and reach maximum widths of ca. 1.2 mm. Leaf cross sections are semicircular in the lower half, where they can be wrapped around >180º circumference of the stem, and become V-shaped distally and secund. The leaf lamina is up to 8 cells wide on each side of the costa and consists of elongated cells with quadrangular cross sections. The costa is up to 42 leucocysts wide. These are lax, devoid of the pores characteristic of some Leucobryum species, and are 32-60 µm (anticlinally) x 17-30 µm (periclinally) in cross section and 40-68 µm long. Leaf cross sections typically display a large central leucocyst abaxially. Chlorocysts are triangular in cross section (with 7-16 µm sides) and ca. 50 µm long. Despite striking overall similarities of this Apple Bay moss with Leucobryum,the combination of three characters - (1) costa only two leucocyst layers thick throughout, (2) presence of conducting strand, (3) distinct epidermis-cortex differentiation - excludes the majority of extant Leucobryum species from direct comparisons. The Apple Bay moss is most similar to L. sericeum, L. sumatranum,and L. arfakianum. However, it differs from these and all other Leucobryum species by the triangular shape and alternate cross-sectional arrangement of chlorocysts. Whether the Apple Bay moss belongs in genus Leucobryum or not, it is undoubtedly a representative, the only fossil one, of family Leucobryaceae. As such, it provides a direct calibration point for estimating divergence times within the Dicranidae, as well as a minimum age for moss lineages basal to that group, such as the Polytrichaceae and Sphagnaceae.

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

Keywords:
Leucobryum
moss
fossil
Cretaceous
leucocyst
chlorocyst.

Presentation Type: Oral Paper:Papers for Sections
Session: 9
Location: Union A/Hyatt
Date: Monday, July 9th, 2012
Time: 11:00 AM
Number: 9003
Abstract ID:646


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