Selaginella lepidophylla (Hooker & Greville, 1830) - resurrection plant from Mexico. (public display, Field Museum of Natural History, Chicago, Illinois, USA)

Plants are multicellular, photosynthesizing eucaryotes. Most species occupy terrestrial environments, but they also occur in freshwater and saltwater aquatic environments. The oldest known land plants in the fossil record are Ordovician to Silurian. Land plant body fossils are known in Silurian sedimentary rocks - they are small and simple plants (e.g., Cooksonia). Fossil root traces in paleosol horizons are known in the Ordovician. During the Devonian, the first trees and forests appeared. Earth's initial forestation event occurred during the Middle to Late Paleozoic. Earth's continents have been partly to mostly covered with forests ever since the Late Devonian. Occasional mass extinction events temporarily removed much of Earth's plant ecosystems - this occurred at the Permian-Triassic boundary (251 million years ago) and the Cretaceous-Tertiary boundary (65 million years ago).

The most conspicuous group of living plants is the angiosperms, the flowering plants. They first unambiguously appeared in the fossil record during the Cretaceous. They quickly dominated Earth's terrestrial ecosystems, and have dominated ever since. This domination was due to the evolutionary success of flowers, which are structures that greatly aid angiosperm reproduction.

From exhibit signage:

The clubmosses and their relatives are relicts of a once well developed and abundant group of spore-bearing plants (Lepidodendrales). These ancient clubmosses were treelike, with grasslike leaves and repeatedly branching stems that terminated in large, spore-bearing cones.

Present day clubmosses are small-leaved and inconspicuous, although they are distributed throughout the world. Most tropical species are epiphytes; that is, they grow on other plants. The two best known genera in the temperate zones are Lycopodium (200 species) and Selaginella (700 species).

The resurrection plant is native to Mexico and the southwestern United States. This species is remarkable for its ability to withstand desiccation. Its fronds roll up into a ball when they dry, but when moisture is restored, they spread, become green, and continue to grow. The resurrection plant can dry out and be rewetted over and over with no loss of vigor.

Classification: Plantae, Lycophyta, Lycopodiopsida, Selaginellales, Selaginellaceae

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