Squirrels are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels, marmots, flying squirrels, prairie dogs amongst other rodents. Squirrels are indigenous to the Americas and Africa, were introduced by humans to Australia; the earliest known squirrels date from the Eocene period and are most related to the mountain beaver and to the dormouse among other living rodent families. The word "squirrel", first attested in 1327, comes from the Anglo-Norman esquirel, from the Old French escurel, the reflex of a Latin word sciurus; this Latin word was borrowed from the Ancient Greek word σκίουρος, which means shadow-tailed, referring to the bushy appendage possessed by many of its members. The native Old English word for the squirrel, ācweorna, survived only into Middle English before being replaced; the Old English word is of Common Germanic origin, cognates of which are still used in other Germanic languages, including the German Eichhörnchen, the Norwegian ikorn/ekorn, the Dutch eekhoorn, the Swedish ekorre and the Danish egern.
Squirrels are small animals, ranging in size from the African pygmy squirrel at 7–10 cm in length and just 10 g in weight, to the Laotian giant flying squirrel at 1.08 m in length and the Alpine marmot, which weighs from 5 to 8 kg. Squirrels have slender bodies with bushy tails and large eyes. In general, their fur is silky, though much thicker in some species than others; the coat color of squirrels is variable between—and even within—species. In most squirrel species, the hind limbs are longer than the fore limbs, while all species have either four or five toes on each paw; the paws, which include an poorly developed thumb, have soft pads on the undersides and versatile, sturdy claws for grasping and climbing. Tree squirrels, unlike most mammals, can descend a tree head-first, they do so by rotating their ankles 180 degrees, enabling the hind paws to point backward and thus grip the tree bark from the opposite direction. Squirrels live in every habitat, from tropical rainforest to semiarid desert, avoiding only the high polar regions and the driest of deserts.
They are predominantly herbivorous, subsisting on seeds and nuts, but many will eat insects and small vertebrates. As their large eyes indicate, squirrels have an excellent sense of vision, important for the tree-dwelling species. Many have a good sense of touch, with vibrissae on their limbs as well as their heads; the teeth of sciurids follow the typical rodent pattern, with large incisors that grow throughout life, cheek teeth that are set back behind a wide gap, or diastema. The typical dental formula for sciurids is 184.108.40.206.0.1.3. Many juvenile squirrels die in the first year of life. Adult squirrels can have a lifespan of 5 to 10 years in the wild; some can survive 10 to 20 years in captivity. Premature death may be caused when a nest falls from the tree, in which case the mother may abandon her young if their body temperature is not correct. Many such baby squirrels have been rescued and fostered by a professional wildlife rehabilitator until they could be safely returned to the wild, although the density of squirrel populations in many places and the constant care required by premature squirrels means that few rehabilitators are willing to spend their time doing this and such animals are euthanized instead.
Squirrels mate either once or twice a year and, following a gestation period of three to six weeks, give birth to a number of offspring that varies by species. The young are altricial, being born naked and blind. In most species of squirrel, the female alone looks after the young, which are weaned at six to ten weeks and become sexually mature by the end of their first year. In general, the ground-dwelling squirrel species are social living in well-developed colonies, while the tree-dwelling species are more solitary. Ground squirrels and tree squirrels are either diurnal or crepuscular, while the flying squirrels tend to be nocturnal—except for lactating flying squirrels and their young, which have a period of diurnality during the summer; because squirrels cannot digest cellulose, they must rely on foods rich in protein and fats. In temperate regions, early spring is the hardest time of year for squirrels because the nuts they buried are beginning to sprout, while many of the usual food sources have not yet become available.
During these times, squirrels rely on the buds of trees. Squirrels, being herbivores, eat a wide variety of plants, as well as nuts, conifer cones, fruits and green vegetation; some squirrels, however consume meat when faced with hunger. Squirrels have been known to eat small birds, young snakes, smaller rodents, as well as bird eggs and insects. Indeed, some tropical squirrel species have shifted entirely to a diet of insects. Predatory behavior has been observed in various species of ground squirrels, in particular the thirteen-lined ground squirrel. For example, Bailey, a scientist in the 1920s, observed a thirteen-lined ground squirrel preying upon a young chicken. Wistrand reported seeing this same species eating a freshly killed snake. Whitaker examined the stomachs of 139 thirteen-lined ground squirrels and found bird flesh in four of the specimens and the remains of a short-tailed shrew in one.
Cephalotaxaceae is a small grouping of conifers, with three genera and about 20 species allied to the Taxaceae, included in that family by some botanists. They are restricted to east Asia, except for two species of Torreya found in the southwest and southeast of the United States; the differences between Taxaceae and Cephalotaxaceae are notable in the cone aril, which encloses the seeds of Cephalotaxaceae, the longer maturation of Cephalotaxaceae seeds and the larger size of the mature seeds. These are much branched, small shrubs; the leaves are evergreen, spirally arranged twisted at the base to appear biranked. They are linear to lanceolate, have pale green or white stomatal bands on the undersides; the plants are subdioecious, or dioecious. The male cones are 4–25 mm long, shed pollen in the early spring; the female cones are reduced, with one to a few ovuliferous scales, one seed on each ovuliferous scale. As the seed matures, the ovuliferous scale develops into a fleshy aril enclosing the seed.
The mature aril is thin, purple or red and resinous. Each ovuliferous scale remains discrete, so the cone develops into a short stem with one to a few berry-like seeds, they are eaten by birds or other animals which disperse the hard seed undamaged in their droppings, but seed dispersal mechanisms in the family are not yet well researched. Images Arboretum de Villardebelle - Cephalotaxus koreana with mature seed cones Arboretum de Villardebelle - Cephalotaxus fortunei with male cones Arboretum de Villardebelle - Torreya californica with seed cones
A seed is an embryonic plant enclosed in a protective outer covering. The formation of the seed is part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosperm plants. Seeds are the product of the ripened ovule, after fertilization by pollen and some growth within the mother plant; the embryo is developed from the seed coat from the integuments of the ovule. Seeds have been an important development in the reproduction and success of gymnosperm and angiosperm plants, relative to more primitive plants such as ferns and liverworts, which do not have seeds and use water-dependent means to propagate themselves. Seed plants now dominate biological niches on land, from forests to grasslands both in hot and cold climates; the term "seed" has a general meaning that antedates the above – anything that can be sown, e.g. "seed" potatoes, "seeds" of corn or sunflower "seeds". In the case of sunflower and corn "seeds", what is sown is the seed enclosed in a shell or husk, whereas the potato is a tuber.
Many structures referred to as "seeds" are dry fruits. Plants producing berries are called baccate. Sunflower seeds are sometimes sold commercially while still enclosed within the hard wall of the fruit, which must be split open to reach the seed. Different groups of plants have other modifications, the so-called stone fruits have a hardened fruit layer fused to and surrounding the actual seed. Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent seed, such as an acorn or hazelnut. Seeds are produced in several related groups of plants, their manner of production distinguishes the angiosperms from the gymnosperms. Angiosperm seeds are produced in a hard or fleshy structure called a fruit that encloses the seeds for protection in order to secure healthy growth; some fruits have layers of both fleshy material. In gymnosperms, no special structure develops to enclose the seeds, which begin their development "naked" on the bracts of cones. However, the seeds do become covered by the cone scales.
Seed production in natural plant populations varies from year to year in response to weather variables and diseases, internal cycles within the plants themselves. Over a 20-year period, for example, forests composed of loblolly pine and shortleaf pine produced from 0 to nearly 5 million sound pine seeds per hectare. Over this period, there were six bumper, five poor, nine good seed crops, when evaluated for production of adequate seedlings for natural forest reproduction. Angiosperm seeds consist of three genetically distinct constituents: the embryo formed from the zygote, the endosperm, triploid, the seed coat from tissue derived from the maternal tissue of the ovule. In angiosperms, the process of seed development begins with double fertilization, which involves the fusion of two male gametes with the egg cell and the central cell to form the primary endosperm and the zygote. Right after fertilization, the zygote is inactive, but the primary endosperm divides to form the endosperm tissue.
This tissue becomes the food the young plant will consume until the roots have developed after germination. After fertilization the ovules develop into the seeds; the ovule consists of a number of components: The funicle or seed stalk which attaches the ovule to the placenta and hence ovary or fruit wall, at the pericarp. The nucellus, the remnant of the megasporangium and main region of the ovule where the megagametophyte develops; the micropyle, a small pore or opening in the apex of the integument of the ovule where the pollen tube enters during the process of fertilization. The chalaza, the base of the ovule opposite the micropyle, where integument and nucellus are joined together; the shape of the ovules as they develop affects the final shape of the seeds. Plants produce ovules of four shapes: the most common shape is called anatropous, with a curved shape. Orthotropous ovules are straight with all the parts of the ovule lined up in a long row producing an uncurved seed. Campylotropous ovules have a curved megagametophyte giving the seed a tight "C" shape.
The last ovule shape is called amphitropous, where the ovule is inverted and turned back 90 degrees on its stalk. In the majority of flowering plants, the zygote's first division is transversely oriented in regards to the long axis, this establishes the polarity of the embryo; the upper or chalazal pole becomes the main area of growth of the embryo, while the lower or micropylar pole produces the stalk-like suspensor that attaches to the micropyle. The suspensor absorbs and manufactures nutrients from the endosperm that are used during the embryo's growth; the main components of the embryo are: The cotyledons, the seed leaves, attached to the embryonic axis. There may be two; the cotyledons are the source of nutrients in the non-endospermic dicotyledons, in which case they replace the endosperm, are thick and leathery. In endospermic seeds the cotyledons are papery. Dicotyledons have the point of attachment opposite one another on the axis; the epicotyl, the embryonic axis above the point of attachment of the cotyledon.
The plumule, the tip of the epicotyl, has a feathery appearance due to the presence of young leaf primordia at the apex, will become the shoot upon germination. The hypocotyl, the embryonic axis below the point of attachment of the cotyledon, connecting the epicotyl and the radicle, being the stem-root transition zone; the radicle, the basal tip of the hy
Cephalotaxus sinensis is a coniferous shub or small tree in the plum yew family. It is native to southern China; some botanists consider Cephalotaxus koreana and C. sinensis to be synonymous with Cephalotaxus harringtonii
A leaf is an organ of a vascular plant and is the principal lateral appendage of the stem. The leaves and stem together form the shoot. Leaves are collectively referred to as foliage, as in "autumn foliage". A leaf is a thin, dorsiventrally flattened organ borne above ground and specialized for photosynthesis. In most leaves, the primary photosynthetic tissue, the palisade mesophyll, is located on the upper side of the blade or lamina of the leaf but in some species, including the mature foliage of Eucalyptus, palisade mesophyll is present on both sides and the leaves are said to be isobilateral. Most leaves have distinct upper surface and lower surface that differ in colour, the number of stomata, the amount and structure of epicuticular wax and other features. Leaves can have many different shapes and textures; the broad, flat leaves with complex venation of flowering plants are known as megaphylls and the species that bear them, the majority, as broad-leaved or megaphyllous plants. In the clubmosses, with different evolutionary origins, the leaves are simple and are known as microphylls.
Some leaves, such as bulb scales, are not above ground. In many aquatic species the leaves are submerged in water. Succulent plants have thick juicy leaves, but some leaves are without major photosynthetic function and may be dead at maturity, as in some cataphylls and spines. Furthermore, several kinds of leaf-like structures found in vascular plants are not homologous with them. Examples include flattened plant stems called phylloclades and cladodes, flattened leaf stems called phyllodes which differ from leaves both in their structure and origin; some structures of non-vascular plants function much like leaves. Examples include the phyllids of liverworts. Leaves are the most important organs of most vascular plants. Green plants are autotrophic, meaning that they do not obtain food from other living things but instead create their own food by photosynthesis, they capture the energy in sunlight and use it to make simple sugars, such as glucose and sucrose, from carbon dioxide and water. The sugars are stored as starch, further processed by chemical synthesis into more complex organic molecules such as proteins or cellulose, the basic structural material in plant cell walls, or metabolised by cellular respiration to provide chemical energy to run cellular processes.
The leaves draw water from the ground in the transpiration stream through a vascular conducting system known as xylem and obtain carbon dioxide from the atmosphere by diffusion through openings called stomata in the outer covering layer of the leaf, while leaves are orientated to maximise their exposure to sunlight. Once sugar has been synthesized, it needs to be transported to areas of active growth such as the plant shoots and roots. Vascular plants transport sucrose in a special tissue called the phloem; the phloem and xylem are parallel to each other but the transport of materials is in opposite directions. Within the leaf these vascular systems branch to form veins which supply as much of the leaf as possible, ensuring that cells carrying out photosynthesis are close to the transportation system. Leaves are broad and thin, thereby maximising the surface area directly exposed to light and enabling the light to penetrate the tissues and reach the chloroplasts, thus promoting photosynthesis.
They are arranged on the plant so as to expose their surfaces to light as efficiently as possible without shading each other, but there are many exceptions and complications. For instance plants adapted to windy conditions may have pendent leaves, such as in many willows and eucalyptss; the flat, or laminar, shape maximises thermal contact with the surrounding air, promoting cooling. Functionally, in addition to carrying out photosynthesis, the leaf is the principal site of transpiration, providing the energy required to draw the transpiration stream up from the roots, guttation. Many gymnosperms have thin needle-like or scale-like leaves that can be advantageous in cold climates with frequent snow and frost; these are interpreted as reduced from megaphyllous leaves of their Devonian ancestors. Some leaf forms are adapted to modulate the amount of light they absorb to avoid or mitigate excessive heat, ultraviolet damage, or desiccation, or to sacrifice light-absorption efficiency in favour of protection from herbivory.
For xerophytes the major constraint drought. Some window plants such as Fenestraria species and some Haworthia species such as Haworthia tesselata and Haworthia truncata are examples of xerophytes. and Bulbine mesembryanthemoides. Leaves function to store chemical energy and water and may become specialised organs serving other functions, such as tendrils of peas and other legumes, the protective spines of cacti and the insect traps in carnivorous plants such as Nepenthes and Sarracenia. Leaves are the fundamental structural units from which cones are constructed in gymnosperms and from which flowers are constructed in flowering plants; the internal organisation of most kinds of leaves has evolved to maximise exposure of the photosynthetic organelles, the chloroplasts, to light and to increase the absorption of carbon dioxide while at the same time controlling water loss. Their surfaces are waterproofed by the plant cuticle and gas exchange between the mesophyll cells and the atmosphere is controlled by minute openings called stomata which open or close to regulate the rate exchange of carbon dioxide and water vapour into
The Pinophyta known as Coniferophyta or Coniferae, or as conifers, are a division of vascular land plants containing a single extant class, Pinopsida. They are gymnosperms, cone-bearing seed plants. All extant conifers are perennial woody plants with secondary growth; the great majority are trees. Examples include cedars, Douglas firs, firs, kauri, pines, redwoods and yews; as of 1998, the division Pinophyta was estimated to contain eight families, 68 genera, 629 living species. Although the total number of species is small, conifers are ecologically important, they are the dominant plants over large areas of land, most notably the taiga of the Northern Hemisphere, but in similar cool climates in mountains further south. Boreal conifers have many wintertime adaptations; the narrow conical shape of northern conifers, their downward-drooping limbs, help them shed snow. Many of them seasonally alter their biochemistry to make them more resistant to freezing. While tropical rainforests have more biodiversity and turnover, the immense conifer forests of the world represent the largest terrestrial carbon sink.
Conifers are of great economic value for softwood paper production. The earliest conifers in the fossil record date to the late Carboniferous period arising from Cordaites, a genus of seed-bearing Gondwanan plants with cone-like fertile structures. Pinophytes and Ginkgophytes all developed at this time. An important adaptation of these gymnosperms was allowing plants to live without being so dependent on water. Other adaptations are pollen and the seed, which allows the embryo to be transported and developed elsewhere. Conifers appear to be one of the taxa that benefited from the Permian–Triassic extinction event, were the dominant land plants of the Mesozoic, they were overtaken by the flowering plants, which first appeared in the Cretaceous, became dominant in the Cenozoic era. They were the main food of herbivorous dinosaurs, their resins and poisons would have given protection against herbivores. Reproductive features of modern conifers had evolved by the end of the Mesozoic era. Conifer is a Latin word, a compound of conus and ferre, meaning "the one that bears cone".
The division name Pinophyta conforms to the rules of the International Code of Nomenclature for algae and plants, which state that the names of higher taxa in plants are either formed from the name of an included family, in this case Pinaceae, or are descriptive. A descriptive name in widespread use for the conifers is Coniferae. According to the ICN, it is possible to use a name formed by replacing the termination -aceae in the name of an included family, in this case preferably Pinaceae, by the appropriate termination, in the case of this division ‑ophyta. Alternatively, "descriptive botanical names" may be used at any rank above family. Both are allowed; this means that if conifers are considered a division, they may be called Coniferae. As a class they may be called Coniferae; as an order they may be called Coniferae or Coniferales. Conifers are the largest and economically most important component group of the gymnosperms, but they comprise only one of the four groups; the division Pinophyta consists of just one class, which includes both living and fossil taxa.
Subdivision of the living conifers into two or more orders has been proposed from time to time. The most seen in the past was a split into two orders and Pinales, but recent research into DNA sequences suggests that this interpretation leaves the Pinales without Taxales as paraphyletic, the latter order is no longer considered distinct. A more accurate subdivision would be to split the class into three orders, Pinales containing only Pinaceae, Araucariales containing Araucariaceae and Podocarpaceae, Cupressales containing the remaining families, but there has not been any significant support for such a split, with the majority of opinion preferring retention of all the families within a single order Pinales, despite their antiquity and diverse morphology; the conifers are now accepted as comprising seven families, with a total of 65–70 genera and 600–630 species. The seven most distinct families are linked in the box above right and phylogenetic diagram left. In other interpretations, the Cephalotaxaceae may be better included within the Taxaceae, some authors additionally recognize Phyllocladaceae as distinct from Podocarpaceae.
The family Taxodiaceae is here included in family Cupressaceae, but was recognized in the past and can still be found in many field guides. A new classification and linear sequence based on molecular data can be found in an article by Christenhusz et al; the conifers are an ancient group, with a fossil record extending back about 300 million years to the Paleozoic in the late Carboniferous period. Other classes and orders, now long extinct occur as fossils from the late Paleozoic and Mesozoic eras. Fossil conifers included many diverse forms, the most distinct from modern conifers being some herbaceous conifers with no woody stems. Major fossil orders of conifers or conifer-like plants include the Cordaitales, Vojnovskyales and also the Czekanowskiales (possibly
A nut is a fruit composed of an inedible hard shell and a seed, edible. In general usage, a wide variety of dried seeds are called nuts, but in a botanical context "nut" implies that the shell does not open to release the seed; the translation of "nut" in certain languages requires paraphrases, as the word is ambiguous. Most seeds come from fruits that free themselves from the shell, unlike nuts such as hazelnuts and acorns, which have hard shell walls and originate from a compound ovary; the general and original usage of the term is less restrictive, many nuts, such as almonds, pistachios and Brazil nuts, are not nuts in a botanical sense. Common usage of the term refers to any hard-walled, edible kernel as a nut. Nuts are an nutrient-rich food source. A nut in botany is a simple dry fruit in which the ovary wall becomes hard as it matures, where the seed remains unattached or free within the ovary wall. Most nuts come from the pistils with inferior ovaries and all are indehiscent. True nuts are produced, by some plant families of the order Fagales.
Order Fagales Family Fagaceae Beech Chestnut Oak Stone-oak Tanoak Family Betulaceae Hazel, Filbert Hornbeam A small nut may be called a "nutlet". In botany, this term refers to a pyrena or pyrene, a seed covered by a stony layer, such as the kernel of a drupe. Walnuts and hickories have fruits, they are considered to be nuts under some definitions, but are referred to as drupaceous nuts. "Tryma" is a specialized term for hickory fruits. In common use, a "tree nut" is, as the name implies; this most comes up regarding allergies, where some people are allergic to peanuts, others to a wider range of nuts that grow in trees. A nut in cuisine is a much less restrictive and older meaning of the word than the narrow meaning of nut in botany. Any large, oily kernels found within a shell and used in food are called nuts. Nuts are an important source of nutrients for wildlife; because nuts have a high oil content, they are a prized food and energy source. A large number of seeds are edible by humans and used in cooking, eaten raw, sprouted, or roasted as a snack food, or pressed for oil, used in cookery and cosmetics.
Nuts used for food, are among the most common food allergens. Some fruits and seeds that do not meet the botanical definition but are nuts in the culinary sense are: Almonds are the edible seeds of drupe fruits – the leathery "flesh" is removed at harvest. Brazil nut is the seed from a capsule. Candlenut is a seed. Cashew is the seed of a drupe fruit with an accessory fruit. Chilean hazelnut or Gevuina. Macadamia is a creamy white kernel of a follicle type fruit. Malabar chestnut. Mongongo nut. Peanut is a seed and from a legume type fruit. Pecan is the seed of a drupe fruit. Pili nut is the seed of the tropical tree Canarium ovatum which grows in the Philippines and Papua New Guinea. Pine nut is the seed of several species of pine. Pistachio is the dehiscent seed of a thin-shelled drupe. Walnut is the seed of a drupe fruit. Yeheb nut is the seed of a desert bush, Cordeauxia edulis. Nuts are the source of energy and nutrients for the new plant, they contain a large quantity of calories, essential unsaturated and monounsaturated fats including linoleic acid and linolenic acid and essential amino acids.
Many nuts are good sources of vitamin E, vitamin B2, folate and the essential minerals magnesium, potassium and selenium. Nuts are most healthy in their raw unroasted form because roasting can damage and destroy fats during the process; this table lists the percentage of various nutrients in four unroasted seeds. Nuts are under preliminary research to assess whether their consumption may lower risk for some diseases, such as cardiovascular diseases and cancer. Nuts have a low glycemic index due to their high unsaturated fat and protein content and low carbohydrate content; the nut of the horse-chestnut tree, is called a conker in the British Isles. Conkers are inedible to many animals because they contain toxic glucoside aesculin, they are used in a popular children's game, known as conkers, where the nuts are threaded onto a strong cord and each contestant attempts to break their opponent's conker by hitting it with their own. Horse chestnuts are popular slingshot ammunition. List of culinary nuts List of edible seeds List of foods Nutmeg Achene Albala, Ken 2014.
Nuts A Global History. The Edible Series. ISBN 978-1-78023-282-9