leaf, chief food-manufacturing organ of a plant, a lateral outgrowth of the growing point of stem. The typical leaf consists of a stalk (the petiole) and a blade—the thin, flat, expanded portion (needlelike in most conifers) that is normally green in color because of the presence of the pigment chlorophyll. In many leaves, small processes called stipules occur at the base of the stalk and protect the bud; sometimes the stipule is large (as in the Japanese quince) and, if green, also manufactures food. The leaf blade is veined with sap-conducting tubes (xylem and phloem) with thick-walled supporting cells. The blade consists of an upper and a lower layer of closely fitted epidermal cells, including specialized paired guard cells that control the size of tiny pores, or stomata, for gaseous exchange and the release of water vapor (see transpiration). The upper epidermis is usually coated with a waterproof cuticle and contains fewer stomata than the underside, if any at all. Between these two layers are large palisade and spongy cells, rich in chlorophyll for food manufacture (see photosynthesis) and permeated with interconnecting air passages leading to the stomata. Leaves vary in size (up to 60 ft/18m long in some palms), shape, venation, color, and texture, and are classified as simple (one blade) or compound (divided into leaflets). The blade margins may be entire (smooth and unindented), toothed (with small sharp or wavy indentations), or lobed (with large indentations, or sinuses). In monocotyledonous plants, the veins are usually parallel; dicotyledons have leaves with reticulately branched veins that may be pinnate (with one central vein, the midrib, and smaller branching veins) or palmate (with several large veins branching from the leaf base into the blade). Pigments besides chlorophyll that give a leaf its characteristic color are the carotenoids (orange-red and yellow), the anthocyanins (red, purple, and blue), and the tannins (brown). White results from the absence of pigments. In deciduous plants, a layer of cells forms the abscission tissue at the base of the stalk in the autumn, cutting off the flow of sap; the unstable chlorophyll disintegrates and, in a temperate zone, the remaining pigments are displayed to produce colorful fall foliage. When these cells dry up completely, the leaf falls. Evergreen plants usually produce new leaves as soon as the old ones fall; the leaves of most conifers remain on the tree from 2 to 10 years (in some species up to 20 years). Leaves may be modified or specialized for protection (spines and bud scales), climbing (tendrils), trapping insects (as in pitcher plants), water storage (as in succulents), or food storage (bulb scales and, in the embryo plantlet, cotyledons).
or walking leaf

Any of about 25 species of flat green insects (family Phylliidae) with a leaflike appearance. Leaf insects, which range from India to the Fiji Islands, are about 2.3 in. (60 mm) long. The female has large leathery forewings (tegmina) that lie edge to edge on the abdomen and resemble, in their vein pattern, the midrib and veins in a leaf. The hind wings have no function. The male has small tegmina and ample, non-leaflike, functional hind wings. The newly hatched young are reddish, but become green after feeding on leaves.

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(Top) Monocotyledon (internal structures of a corn seed with stages of germination). Nutrients are elipsis

Seed leaf within the embryo of a seed that provides energy and nutrients for the developing seedling. After the first true leaves have formed, they wither and fall off. Flowering plants whose embryos have a single cotyledon are grouped as monocots, or monocotyledonous plants; embryos with two cotyledons are grouped as dicots, or dicotyledonous plants. Unlike flowering plants, gymnosperms usually have several cotyledons rather than one or two.

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Any of various insect larvae that live and feed within a leaf, including caterpillars, sawfly larvae, beetle and weevil grubs, and dipteran maggots. Most leaf-miner burrows or tunnels are either thin, winding, whitish trails or broad, whitish or brownish blotches. Though leaf miners do not usually cause injury, they mar the appearance of ornamental trees and shrubs. One method of control is to remove and burn infested leaves; spraying with nicotine solutions or dusting with insecticides is effective only when the adults are emerging.

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Structures of a leaf

Any flattened, green outgrowth from the stem of a vascular plant. Leaves manufacture oxygen and glucose, which nourishes and sustains both plants and animals. Leaves and stem tissue grow from the same apical bud. A typical leaf has a broad, expanded blade (lamina), attached to the stem by a stalklike petiole. The leaf may be simple (a single blade), compound (separate leaflets), or reduced to a spine or scale. The edge (margin) may be smooth or jagged. Veins transport materials to and from the leaf tissues, radiating from the petiole through the blade. They are arranged in a netlike pattern in dicot leaves and are parallel in monocot leaves (see cotyledon). The leaf's outer layer (epidermis) protects the interior (mesophyll), whose soft-walled, unspecialized green cells (parenchyma) produce carbohydrate food by photosynthesis. In autumn the green chlorophyll pigments of deciduous leaves break down, revealing other pigment colors (yellow to red), and the leaves drop off the tree. Leaf scars that form during wound healing after the leaves drop are useful for identifying winter twigs. In conifers, evergreen needles, which are a type of leaf, persist for two or three years.

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Leaf-warblers are small insectivorous birds belonging to the genus Phylloscopus. This was placed in the "wastebin" Old World warbler family, but is now moved into a new family Phylloscopidae (Alström et al. 2006). There are presently some 55 species in the genus, but this composition makes it polyphyletic with regards to Seicercus. Thus, several species will soon be moved out of the present genus.

These are active, constantly moving, warblers always associated with trees, though normally in fairly open woodland rather than tight plantations. They occur from top canopy to undershrubs. Most of the species are markedly territorial both in their summer and winter quarters.

Most are greenish or brownish above and off-white or yellowish below. Compared to some other "warblers", their songs are very simple

Species breeding in temperate regions are usually strongly migratory.

The species traditionally placed in Phylloscopus are:


  • Alström, Per; Ericson, Per G.P.; Olsson, Urban & Sundberg, Per (2006): Phylogeny and classification of the avian superfamily Sylvioidea. Molecular Phylogenetics and Evolution 38(2): 381–397.
  • Badyaev Alexander V. & Leaf, Elizabeth S. (1997): Habitat associations of song characteristics in Phylloscopus and Hippolais warblers. Auk 114(1): 40-46. PDF fulltext
  • Del Hoyo, J.; Elliot, A. & Christie D. (editors). (2006). Handbook of the Birds of the World. Volume 11: Old World Flycatchers to Old World Warblers. Lynx Edicions. ISBN 849655306X.

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