Evapotranspiration‐linked silica deposition in a basal tracheophyte plant (Lycopodiaceae: Lycopodiella alopecuroides): implications for the evolutionary origins of phytoliths

Abstract

Summary Phytoliths, microscopic deposits of hydrated silica within plants, play a myriad of functional roles in extant tracheophytes – yet their evolutionary origins and the original selective pressures leading to their deposition remain poorly understood. To gain new insights into the ancestral condition of tracheophyte phytolith production and function, phytolith content was intensively assayed in a basal, morphologically conserved tracheophyte: the foxtail clubmoss Lycopodiella alopecuroides. Wet ashing was employed to perform phytolith extractions from every major anatomical region of L. alopecuroides. Phytolith occurrence was recorded, alongside abundance, morphometric information, and morphological descriptions. Phytoliths were recovered exclusively from the microphylls, which were apicodistally silicified into multiphytolith aggregates. Phytolith aggregates were larger and more numerous in anatomical regions engaging in greater evapotranspirational activity. The tissue distribution of L. alopecuroides phytoliths is inconsistent with the expectations of proposed adaptive hypotheses of phytolith evolutionary origin. Instead, it is hypothesized that phytoliths may have arisen incidentally in the L. alopecuroides‐like ancestral plant, polymerizing from intraplant silicon accumulations arising via bulk flow and ‘leaky’ cellular micronutrient channels. This basal, nonadaptive phytolith formation model would provide the evolutionary ‘raw material’ for later modification into the useful, adaptative, phytolith deposits seen in later‐diverging plant clades.

Is there silicon in flowers and what does it tell us?

“…Whalen et al. ( 2023 ) deduced from a study of phytolith production in a basal, morphologically conserved vascular plant species ( Lycopodiella alopecuroides ) that silica deposition initially occurred incidentally with passive uptake, and Si deposited at transpiration termini, and adaptations for functional silicon use by plants evolved subsequently. Trembath‐Reichert et al.…”