BIOGENIC SILICA IN THE PINACEAE

Abstract

Biogenic opal was isolated in measurable quantities from 15 taxa [Pinus strobus, P. resinosa, P. banksiana, P. sylvestris, Larix laricina, L. decidua, Picea rubens, P. mariana, P. glauca, Pseudotsuga menziesii var. glauca, P. menziesii var. verdis, Tsuga canadensis, T. caroliniana, Abies balsamea and A. fraseri] of the family Pinaceae. Opal contents varied from 0.08% of dry wt in P. resinosa to 1.37% in L. decidua. The silica content of a widely ranging species, T. canadensis, varied significantly with collection location in New York State [USA], but the causes of variation were not investigated. All cell types in Pinaceae leaves may become weakly silicified, resulting in cellular fragments upon digestion, or heavily silicified, resulting in well-preserved cellular replicas. Epidermal phytoliths formed in interstomatal files are the most common cellular particles in the wet ash silica residue. Vascular cells (both tracheary elements and transfusion parenchyma), fibers, asterosclerids, mesophyll cells and endodermal cells were also represented in the ash of some species. Differences in the opal residue from different genera were observed, with endodermal polyhedrons limited to Picea, asterosclereids exclusive to Pseudotsuga, and epidermal cells with distinctly undulating margins present in Pinus, Tsuga and Abies. Marginal undulations on the epidermal cells of Picea, Larix and Pseudotsuga are less pronounced. Opal from Pinaceae leaves may be most readily separated from that of other plant materials by the presence of transfusion tissue tracheids with bordered pit impressions and tapering ends. Epidermal cells are also distinctive, although careful study will be required to differentiate them from the epidermal long cells and costal rods of grasses. Other particles may also be utilized in areas where the diversity of previous vegetative occupants was limited.