Plants most-likely evolved from green algae. First land plants appeared about 475 mya; first vascular plants appeared about 420 mya; first seed plants appeared about 360 mya. Fossil evidence of plants includes that of leaves (some with venation preserved), stems, cones, seeds, tree bark and trunks. Flowers are rare as fossils. Petrified wood, where the tree is replaced cell by cell by a mineral (usually silica) creating an exact replica of the original specimen, are common fossils found in geology collections.