Abstract Detail

Paleobotany

Rothwell, Gar [1], Stockey, Ruth [2].

Herbaceous lycophtytes of the Early Cretaceous Apple Bay assemblage, Vancouver Island, British Columbia,, Canada.

Among the unusually diverse assemblage of vascular plants, bryophytes, and fungi that occurs within marine carbonate concretions from Early Cretaceous (Valanginian) deposits at Apple Bay on northern Vancouver Island are vegetative remains that conform both to Lycopodiales and Selaginellales. Lycopodiales is represented by plectostelic stems, some with helically arranged microphylls and some with smooth outer margins of the cortex. One specimen shows anisostomous branching. Stems range 0.4 – 1.1 mm in diameter, with steles that make up ~1/2 of the stem diameter and have 7 - 14 exarch protoxylem strands. The cortex of leafy specimens consists of a heterogeneous combination of parenchyma and sclerenchyma. That of stems with a smooth outer margin is constructed of sclerenchyma with uniformly thick walls in some specimens, and of sclerenchyma with thicker walls at the inner margin in others. Leaves are lenticular immediately distal to the level of divergence. Each leaf has a single central trace, parenchymatous cortex and uniseriate epidermis. Taxonomically informative features including stelar architecture, stelar size, number of protoxylem strands, and cortical histology reveal that Apple Bay lycopodialean specimens conform to the recently described genus Lycopodicaulis from Barremian/Earliest Aptian deposits of Mongolia, thus extending the known stratigraphic range of that genus to the Valanginian Stage of the Early Cretaceous. Selaginellales is represented by an oval stem 1.2 mm wide that conforms to species of the genus Selaginella that have two or more meristeles. The Apple Bay stem has three meristeles arranged in a row, parenchymatous cortex, and a uniseriate epidermis. Each meristele has a single protoxylem strand and oval metaxylem. There is a narrow space between each meristele and cortex that conforms to the aerenchymatous pericycle in living species of Selaginella. Fragments of possible trabeculae are present in the space of some sections. Although structural features of several Selaginella species are characterized in the classical literature and summarized in plant morphology textbooks, the ~750 living species of Selaginella are classified into about 18 sections of about six subgenera on the basis of nucleotide sequence characters. Species display a bewildering array of morphological variations with inconsistent distributions across the sections such that it is difficult to interpret the subgeneric relationships of fossil species that are represented by anatomical sections. At the present time, living species with three cauline meristeles are confined to Subgenera Gymnogynum (S. articulata) and Stachygynandrium (23+ species).

1 - Oregon State University, Department Of Botany And Plant Pathology, 2082 Cordley Hall, Corvallis, OR, 97331, United States
2 - Oregon State University, Botany and Plant Pathology, 2081 Cordley Hall Oregon State University, Corvallis, United States, 97331, USA

Keywords:
Anatomy
Lycopodiales
Lycopodicaulis
Selaginella
Selaginellales
Early Cretaceous.

Presentation Type: Oral Paper
Number: PB4002
Abstract ID:69
Candidate for Awards:None