Additional bryophyte diversity in the Lower Cretaceous of Vancouver Island(British Columbia, Canada): an anatomically-preserved tristichous moss

SAVORETTI ADOLFINA; BIPPUS ALEXANDER; STOCKEY RUTH A.; ROTHWELL GAR W.; TOMESCU ALEXANDRU

Fort Worth, Texas

Congreso; Botany 2017; 2017

Botany Conference

The Early Cretaceous Apple Bay flora of Vancouver Island (Valanginian, 136 Ma) comprisespermineralized plant assemblages preserved in carbonate concretions. This flora has yieldedrepresentatives of most major vascular plants groups, a lichen, and several fungi. A widevariety of bryophytes is present, making this one of the most diverse fossil bryophyte florasworldwide. Notable within the assemblage are polytrichaceous and leucobryaceous mosses,as well as hypnanaean tricostate mosses. A new bryophyte type identified at Apple Bay ischaracterized by very small gametophytes. The stem, 500 µm in diameter (including leafbases), is triquetrous and branches three-dimensionally at close intervals. This branchingarchitecture indicates an upright growth habit consistent with acrocarpy. The stemepidermis consists of flat cells with thicker walls than the cortical cells. The cortexcomprises 3-4 layers of larger parenchyma and shows a sharp transition, at the center of thestem, to an area that lacks cellular preservation, which suggests the missing cells weredelicate or small and could have formed a conducting strand. Leaves are densely imbricate,with helical tristichous phyllotaxis, and diverge at a sharp angle. Leaves are keeled, withrecurved margins. The lamina is bistratose at the leaf base, becoming partially bistratosedistally along the costa, and eventually unistratose in the upper leaf half. The strong costais attenuate and exhibits some differentiation between thicker-walled epidermal cells andthinner-walled internal cells. This new Apple Bay moss has a distinctive combination offeatures: tristichous helical phyllotaxis and a bistratose leaf lamina. However, given theirbroad but infrequent taxonomic distribution, both of these features are probablyhomoplasic. Each occurs in several extant families: tristichous phyllotaxis in at least 10extant families and bistratose leaf lamina in at least 15 extant families. Of these, fourfamilies (Meesiaceae, Polytrichaceae, Grimmiaceae, Pottiaceae) include species that havetristichous phyllotaxis or bistratose lamina, but not both. Additionally, no extant moss showsbistratose lamina organization similar to that of the Apple Bay moss (bistratose basally,transitioning to unistratose apically): in living mosses, leaves are completely bistratose orthey are bistratose either apically, marginally, in patches, or in streaks. Together, thesesuggest that the Apple Bay fossil represents a distinct moss type with no extant counterpart.This is the fifth moss described from Apple Bay and the third acrocarp type in this bryoflora,adding another element to the rich diversity of this Early Cretaceous flora and to the sparse bryophyte fossil record.