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Premise of research. Climatically favorable conditions correspond with fossil evidence for dramatic Ordovician marine biodiversification, but coeval terrestrial biodiversity is less well understood. Although diverse Middle and Late Ordovician microfossils are interpreted as reproductive remains of early bryophyte-like land plants (consistent with molecular data indicating pre-Ordovician embryophyte origin), the vegetative structure of Ordovician plants remains mysterious, as do relationships to modern groups. Because distinctive fungal microfossils indicating land plant presence were previously reported from Ordovician carbonate deposits in Wisconsin, we examined another nearby outcrop for additional evidence of terrestrial biodiversification. Methodology. Replicate collections were made from well-understood 455-454 Ma Platteville Formation carbonates of relatively low porosity and hydraulic conductivity. We employed measures to avoid contamination, and organic remains extracted by acid maceration were characterized by light and scanning electron microscopy and energy-dispersive X-ray spectroscopy. Pivotal results. Multicellular organic fragments displayed distinctive cellular features shared with modern vegetative peat mosses but differed from modern materials, e.g., fossil presence of mineral coatings, absence of epibionts. Biometric features of mosslike microfossils isolated from carbonates collected and macerated 12 yr apart by separate investigators did not differ. Putative peat moss remains occurred with foraminifera similar in frequency and thermal maturity to types previously described from the same formation. No diatoms, pollen, or other indicators of post-Ordovician environments were observed. Conclusions. The peat moss-like fragments described here are the oldest-known vegetative remains of land plants and the oldest fossils having distinctive features linking them to a modern plant group. These findings are consistent with peat moss recalcitrance properties that foster fossilization and molecular evidence that the peat moss lineage is 460-607 Ma of age. The new findings suggest that moss-dominated peatlandsrecognized for globally significant roles in modern terrestrial biodiversity and C and N cycling-were present hundreds of millions of years earlier than previously thought.

Premise of research. Sphagnum peatmosses strongly influence local and regional hydrology and biotic communities and based on high abundance at high latitudes also play a global environmental role in maintaining atmospheric chemistry and climate homeostasis. Previous field research suggests that elevated temperature linked to global climate change or elevated UV related to ozone depletion at high latitudes affects aspects of peatmoss productivity or external morphology hypothesized to influence environmental roles. However, changes in microscopic anatomy or potential temperature-UV interaction effects have not previously been investigated. Controlled environments offer advantages for assessing anatomical impacts of temperature and UV variation and detecting temperature-UV interactions.Methodology. Clonal cultures of experimentally tractable Sphagnum compactum were treated for a 2-mo period with environmentally relevant temperature levels (107, 207, and 307C) and two levels of UV-A 1 UV-B found in a pilot study to produce contrasting structural effects, in a factorial experimental design. Proportions of hydrolysis-resistant and cellulosic biomass and numerous features of microscopic anatomy having potential ecological significance were assessed and analyzed using two-way ANOVA.Pivotal results. Elevated temperature, the higher level of UV treatment, or temperature-UV interaction significantly influenced survival, biomass, cell wall biochemistry, or anatomical features of ecological significance. Plants grown at 107 or 207C and under the higher level of UV treatment displayed increased proportion of hydrolysis-resistant cell wall material. Elevated temperature was associated with reduction in stem width and reduced numbers of supportive fibrils in branch and stem leaf hyaline cells. Plants exposed to 307C and the higher level of UV treatment died during the treatment period.Conclusions. Elevated temperature, UV, and temperature-UV interactions affect peatmoss biomass, wall chemistry, and anatomy in ways that could influence environmental roles. Functionally important traits affected by temperature or UV are recommended for assessment in field studies.

The environmental influences that determine dorsiventral or axial gametophyte orientation are unknown for most modern seedless plants. To fill this gap, an experimental laboratory system was employed to evaluate the relative effects of light direction and gravity on body orientation of the dorsiventral green alga Coleochaete orbicularis, and gametophytes of liverworts Blasia pusilla and Marchantia polymorpha, early-diverging moss Sphagnum compactum, and fern Ceratopteris richardii, the latter functioning as experimental control. Replicate clonal cultures were experimentally illuminated only from above, only from below, or from multiple directions, with the same near-saturation PAR level for periods brief enough to minimize nutrient limitation effects, and orientation of new growth was evaluated. For all species tested, direction of illumination exerted stronger control over gametophyte body orientation than gravity. When illuminated only from below: 1) axial Sphagnum gametophores that had initially grown into an overlying air space inverted growth by 180, burrowing into the substrate; 2) new growth of dorsiventral Blasia, Marchantia, and Ceratopteris gametophytes-whose ventral rhizoids initially penetrated agar substrate and dorsal surfaces initially faced overlying airspace-twisted 180 so that ventral surfaces bearing rhizoids faced overlying air space and rhizoids extended into the air; and 3) Coleochaete lost typical dorsiventral organization and diagnostic dorsal hairs. Direction of illumination also exerted stronger control over orientation of liverwort new growth than surface contact did. These results indicate that early land plants likely inherited light-directed gametophyte body orientation from ancestral streptophyte algae and suggest a mechanism for reorientation of gametophyte-dominant land plants after spatial disturbance.