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| ple, vascularized leaves (microphylls), such as those of the early Devonian lycopsid Baragwanathia, first evolved as enations, extensions of the stem. True leaves or euphylls of larger size and with more complex venation did not become widespread in other groups until the Devonian period, by which time the carbon dioxide concentration in the atmosphere had dropped significantly. This occurred independently in several separate lineages of vascular plants, in progymnosperms like Archaeopteris, in Sphenopsida, ferns and later in the gymnosperms and angiosperms. Euphylls are also referred to as macrophylls or megaphylls (large leaves). Morphology See also: Glossary of leaf morphology Animated zoom into the leaf of a Sequoia sempervirens (California redwood) Leafstem of dog rose with petiole, stipules and leaflets Rosa canina: Petiole, two stipules, rachis, five leaflets Citrus leaves with translucent glands A structurally complete leaf of an angiosperm consists of a petiole (leaf stalk, called a stipe in ferns), a lamina (leaf blade), stipules (small structures located to either side of the base of the petiole) and a sheath. Not every species produces leaves with all of these structural components. The lamina is the expanded, flat component of the leaf which contains the chloroplasts. The sheath is a structure at the base that fully or partially wraps around the stem, above the node where the leaf is attached. Leaf sheathes typically occur in Poaceae (grasses), Apiaceae (umbellifers), and many palms. Between the sheath and the lamina, there may be a pseudopetiole, a petiole like structure. Pseudopetioles occur in some monocotyledons including bananas, palms and bamb |
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