85-445: Yucca brevifolia (also known as the Joshua tree , yucca palm , tree yucca , and palm tree yucca ) is a plant species belonging to the genus Yucca . It is tree-like in habit, which is reflected in its common names. This monocotyledonous tree is native to the arid Southwestern United States , specifically California , Arizona , Utah , and Nevada , and northwestern Mexico . It
170-468: A biblical story in which Joshua keeps his hands reached out for an extended period of time to enable the Israelites in their conquest of Canaan ( Joshua 8:18–26 ). Further, the shaggy leaves may have provided the appearance of a beard. However, no direct or contemporary attestation of this origin exists, and the name Joshua tree is not recorded until after Mormon contact; moreover, the physical appearance of
255-408: A decussate pattern, in which each node rotates by 1/4 (90°) as in the herb basil . The leaves of tricussate plants such as Nerium oleander form a triple helix. The leaves of some plants do not form helices. In some plants, the divergence angle changes as the plant grows. In orixate phyllotaxis, named after Orixa japonica , the divergence angle is not constant. Instead, it is periodic and follows
340-426: A desert species; new seedlings may grow at an average rate of 7.6 cm (3.0 in) per year in their first 10 years, then only about 3.8 cm (1.5 in) per year. The trunk consists of thousands of small fibers and lacks annual growth rings , making determining the tree's age difficult. This tree has a top-heavy branch system, and a broad root system, with roots in one case found 11 m (36 ft) from
425-431: A high probability that their populations will be reduced by 90% of their current range by the end of the 21st century, thus fundamentally transforming the ecosystem of the park. Wildfires, invasive grasses and poor migration patterns for the trees' seeds are all additional factors in the species' imperilment. As an example, approximately 13%—or more than 1.3 million Joshua trees—in one of the densest Joshua tree populations in
510-504: A petiole like structure. Pseudopetioles occur in some monocotyledons including bananas , palms and bamboos . Stipules may be conspicuous (e.g. beans and roses ), soon falling or otherwise not obvious as in Moraceae or absent altogether as in the Magnoliaceae . A petiole may be absent (apetiolate), or the blade may not be laminar (flattened). The petiole mechanically links the leaf to
595-463: A plant matures; as a case in point Eucalyptus species commonly have isobilateral, pendent leaves when mature and dominating their neighbors; however, such trees tend to have erect or horizontal dorsiventral leaves as seedlings, when their growth is limited by the available light. Other factors include the need to balance water loss at high temperature and low humidity against the need to absorb atmospheric carbon dioxide. In most plants, leaves also are
680-419: A regular organization at the cellular scale. Specialized cells that differ markedly from surrounding cells, and which often synthesize specialized products such as crystals, are termed idioblasts . The epidermis is the outer layer of cells covering the leaf. It is covered with a waxy cuticle which is impermeable to liquid water and water vapor and forms the boundary separating the plant's inner cells from
765-652: A route which has been designated the Joshua Tree Parkway of Arizona. The trees are abundant in Saddleback Butte State Park 135 kilometres (85 miles) north of Downtown Los Angeles in Los Angeles County's Antelope Valley . The common name Joshua tree apparently comes from Christian iconography. The Joshua tree is called "hunuvat chiy'a" or "humwichawa" by the indigenous Cahuilla . It is also called izote de desierto (Spanish, "desert dagger"). It
850-475: A scaffolding matrix imparting mechanical rigidity to leaves. Leaves are normally extensively vascularized and typically have networks of vascular bundles containing xylem , which supplies water for photosynthesis , and phloem , which transports the sugars produced by photosynthesis. Many leaves are covered in trichomes (small hairs) which have diverse structures and functions. The major tissue systems present are These three tissue systems typically form
935-541: A severe dry season, some plants may shed their leaves until the dry season ends. In either case, the shed leaves may be expected to contribute their retained nutrients to the soil where they fall. In contrast, many other non-seasonal plants, such as palms and conifers, retain their leaves for long periods; Welwitschia retains its two main leaves throughout a lifetime that may exceed a thousand years. The leaf-like organs of bryophytes (e.g., mosses and liverworts ), known as phyllids , differ heavily morphologically from
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#17328482273341020-484: A shampoo in Native American rituals. Dried yucca leaves and trunk fibers have a low ignition temperature, making the plant desirable for use in starting fires via friction. The stem (when dried) that sports the flowers is often used in conjunction with a sturdy piece of cedar for fire-making. In rural Appalachian areas, species such as Yucca filamentosa are referred to as "meat hangers". With their sharp-spined tips,
1105-402: A single (sometimes more) primary vein in the centre of the leaf, referred to as the midrib or costa, which is continuous with the vasculature of the petiole. The secondary veins, also known as second order veins or lateral veins, branch off from the midrib and extend toward the leaf margins. These often terminate in a hydathode , a secretory organ, at the margin. In turn, smaller veins branch from
1190-573: A single leaf grows from each node, and when the stem is held straight, the leaves form a helix . The divergence angle is often represented as a fraction of a full rotation around the stem. A rotation fraction of 1/2 (a divergence angle of 180°) produces an alternate arrangement, such as in Gasteria or the fan-aloe Kumara plicatilis . Rotation fractions of 1/3 (divergence angles of 120°) occur in beech and hazel . Oak and apricot rotate by 2/5, sunflowers, poplar, and pear by 3/8, and in willow and almond
1275-523: A single point. In evolutionary terms, early emerging taxa tend to have dichotomous branching with reticulate systems emerging later. Veins appeared in the Permian period (299–252 mya), prior to the appearance of angiosperms in the Triassic (252–201 mya), during which vein hierarchy appeared enabling higher function, larger leaf size and adaption to a wider variety of climatic conditions. Although it
1360-409: A small leaf. Stipules may be lasting and not be shed (a stipulate leaf, such as in roses and beans ), or be shed as the leaf expands, leaving a stipule scar on the twig (an exstipulate leaf). The situation, arrangement, and structure of the stipules is called the "stipulation". Veins (sometimes referred to as nerves) constitute one of the most visible features of leaves. The veins in a leaf represent
1445-405: A specialized cell group known as the stomatal complex. The opening and closing of the stomatal aperture is controlled by the stomatal complex and regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Stomata therefore play the important role in allowing photosynthesis without letting the leaf dry out. In a typical leaf, the stomata are more numerous over
1530-625: A threat to population density of prone areas but not to the limits of the range itself, that several population studies showed Yucca brevifolia was abundant, and that although the southern region of the species' range has been reduced, the trend is that the northern region has been expanding over the last 11,700 years as the North American ice cap melted, allowing the species to occupy its current range. The studies showing reduced population after fires used aerial photography to document populations which would underreport smaller and thus younger trees, as
1615-483: A variety of patterns (venation) and form cylindrical bundles, usually lying in the median plane of the mesophyll , between the two layers of epidermis . This pattern is often specific to taxa, and of which angiosperms possess two main types, parallel and reticulate (net like). In general, parallel venation is typical of monocots, while reticulate is more typical of eudicots and magnoliids (" dicots "), though there are many exceptions. The vein or veins entering
1700-515: A winter freeze before they bloom. Once they bloom, the flowers are pollinated by the yucca moth ( Tegeticula synthetica ), which spreads pollen while laying eggs inside the flower. The larvae feed on the seeds, but enough seeds remain to reproduce. The Joshua tree is also able to actively abort ovaries in which too many eggs have been produced. The Joshua tree is native to the southwestern United States (Arizona, California, Nevada, and Utah) and northwestern Mexico. This range mostly coincides with
1785-402: Is a principal appendage of the stem of a vascular plant , usually borne laterally above ground and specialized for photosynthesis . Leaves are collectively called foliage , as in "autumn foliage", while the leaves, stem, flower, and fruit collectively form the shoot system. In most leaves, the primary photosynthetic tissue is the palisade mesophyll and is located on the upper side of
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#17328482273341870-455: Is called a stipe in ferns . The lamina is the expanded, flat component of the leaf which contains the chloroplasts . The sheath is a structure, typically at the base that fully or partially clasps the stem above the node, where the leaf is attached. Leaf sheathes typically occur in Poaceae (grasses) and Apiaceae (umbellifers). Between the sheath and the lamina, there may be a pseudopetiole ,
1955-576: Is confined mostly to the Mojave Desert between 400 and 1,800 m (1,300 and 5,900 ft) elevation. It thrives in the open grasslands of Queen Valley and Lost Horse Valley in Joshua Tree National Park . Other regions with large populations of the tree can be found northeast of Kingman, Arizona , in Mohave County ; and along U.S. 93 between the towns of Wickenburg and Wikieup ,
2040-656: Is not likely to become an endangered species in the foreseeable future in the absence of special protection and management efforts required by CESA. In February 2023, California governor Gavin Newsom 's administration proposed a budget trailer bill The Western Joshua Tree Conservation Act to focus on protecting the climate-threatened species and permitting development in the Southern California desert . The legislation requires conservation plan for this and other species that may be threatened by climate change and would authorize
2125-531: Is the state flower of New Mexico in the southwest United States. No species name is given in the citation; however, the New Mexico Centennial Blue Book from 2012 references the soaptree yucca ( Yucca elata ) as one of the more widespread species in New Mexico. The Yucca flower is also the national flower of El Salvador , where it is known as flor de izote . As of February 2012 ,
2210-406: Is the more complex pattern, branching veins appear to be plesiomorphic and in some form were present in ancient seed plants as long as 250 million years ago. A pseudo-reticulate venation that is actually a highly modified penniparallel one is an autapomorphy of some Melanthiaceae , which are monocots; e.g., Paris quadrifolia (True-lover's Knot). In leaves with reticulate venation, veins form
2295-599: The Americas and the Caribbean in a wide range of habitats, from humid rainforest and wet subtropical ecosystems to the hot and dry ( arid ) deserts and savanna. Early reports of the species were confused with the cassava ( Manihot esculenta ). Consequently, Linnaeus mistakenly derived the generic name from the Taíno word for the latter, yuca . The Aztecs living in Mexico since before
2380-566: The California Department of Fish and Wildlife to permit taking a western Joshua tree only under certain conditions. The legislation requires a fee of up to $ 2500 for the removal, relocation or trimming of limbs of a Western Joshua tree, including dead trees and limbs. This bill was passed by California lawmakers in June 2023 and went into effect on July 10, 2023. Different forms of the species are cultivated, including smaller plants native from
2465-520: The Curculionidae . Yuccas are widely grown as ornamental plants in gardens. Many species also bear edible parts, including fruits , seeds , flowers , flowering stems , and (more rarely) roots . References to yucca root as food often arise from confusion with the similarly pronounced, but botanically unrelated, yuca, also called cassava or manioc ( Manihot esculenta ). Roots of soaptree yucca ( Yucca elata ) are high in saponins and are used as
2550-494: The diet of many animals . Correspondingly, leaves represent heavy investment on the part of the plants bearing them, and their retention or disposition are the subject of elaborate strategies for dealing with pest pressures, seasonal conditions, and protective measures such as the growth of thorns and the production of phytoliths , lignins , tannins and poisons . Deciduous plants in frigid or cold temperate regions typically shed their leaves in autumn, whereas in areas with
2635-424: The gymnosperms and angiosperms . Euphylls are also referred to as macrophylls or megaphylls (large leaves). A structurally complete leaf of an angiosperm consists of a petiole (leaf stalk), 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 proximal stalk or petiole
Yucca brevifolia - Misplaced Pages Continue
2720-551: The phyllids of mosses and 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 then stored as starch , further processed by chemical synthesis into more complex organic molecules such as proteins or cellulose ,
2805-399: 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 usually in opposite directions. Within the leaf these vascular systems branch (ramify) to form veins which supply as much of the leaf as possible, ensuring that cells carrying out photosynthesis are close to
2890-832: The Joshua tree more closely resembles a similar story told of Moses . Ranchers and miners who were contemporaneous with the Mormon immigrants used the trunks and branches as fencing and for fuel for ore-processing steam engines. In addition to the autonymic subspecies Y. b. subsp. brevifolia , two other subspecies have been described: Y. b. subsp. herbertii (Webber's yucca or Herbert Joshua tree) and Y. b. subsp. jaegeriana (the Jaeger Joshua tree or Jaeger's Joshua tree or pygmae yucca), though both are sometimes treated as varieties or forms . Y.b. subsp. jaegeriana has also been treated as its own species. Joshua trees grow quickly for
2975-525: The Spanish arrival, in Nahuatl , call the local yucca species ( Yucca gigantea ) iczotl , which gave the Spanish izote . Izote is also used for Yucca filifera . The natural distribution range of the genus Yucca (49 species and 24 subspecies) covers a vast area of the Americas . The genus is represented throughout Mexico and extends into Guatemala ( Yucca guatemalensis ). It also extends to
3060-508: The World Checklist of Selected Plant Families recognizes 49 species of Yucca and several hybrids: A number of other species previously classified in Yucca are now classified in the genera Dasylirion , Furcraea , Hesperaloe , Hesperoyucca , and Nolina . From 1897 to 1907, Carl Ludwig Sprenger created and named 122 Yucca hybrids. Leaf A leaf ( pl. : leaves )
3145-679: The amount of light they absorb to avoid or mitigate excessive heat, ultraviolet damage, or desiccation, or to sacrifice light-absorption efficiency in favor of protection from herbivory. For xerophytes the major constraint is not light flux or intensity , but 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 also function to store chemical energy and water (especially in succulents ) and may become specialized organs serving other functions, such as tendrils of peas and other legumes,
3230-444: The base, tapering to a sharp point; they are borne in a dense spiral arrangement at the apex of the stems. The leaf margins are white and serrated . Flowers typically appear from February to late April, in panicles 30 to 55 cm tall and 30 to 38 cm broad, the individual flowers erect, 4 to 7 cm tall, with six creamy white to green tepals . The tepals are lanceolate and are fused to the middle. The fused pistils are 3 cm tall and
3315-583: The basic structural material in plant cell walls, or metabolized 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 ( epidermis ), while leaves are orientated to maximize their exposure to sunlight. Once sugar has been synthesized, it needs to be transported to areas of active growth such as
3400-452: The blade attaches directly to the stem. Subpetiolate leaves are nearly petiolate or have an extremely short petiole and may appear to be sessile. In clasping or decurrent leaves, the blade partially surrounds the stem. When the leaf base completely surrounds the stem, the leaves are said to be perfoliate , such as in Eupatorium perfoliatum . In peltate leaves, the petiole attaches to
3485-406: The blade inside the blade margin. In some Acacia species, such as the koa tree ( Acacia koa ), the petioles are expanded or broadened and function like leaf blades; these are called phyllodes . There may or may not be normal pinnate leaves at the tip of the phyllode. A stipule , present on the leaves of many dicotyledons , is an appendage on each side at the base of the petiole, resembling
Yucca brevifolia - Misplaced Pages Continue
3570-485: 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 are flattened and have distinct upper ( adaxial ) and lower ( abaxial ) surfaces that differ in color, hairiness, the number of stomata (pores that intake and output gases), the amount and structure of epicuticular wax and other features. Leaves are mostly green in color due to
3655-453: The deserts of North America being regarded as the center of diversity for the genus. Yuccas have a very specialized, mutualistic pollination system; being pollinated by yucca moths (family Prodoxidae ); the insect transfers the pollen from the stamens of one plant to the stigma of another, and at the same time lays an egg in the flower; the moth larva then feeds on some of the developing seeds, always leaving enough seed to perpetuate
3740-595: 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
3825-756: The eastern part of the species range. These smaller plants grow 2.5 m tall and branch when about 1 m tall. Red-shafted flickers make nests in the branches, which are later used by other birds. Prior to the twentieth century, Native Americans of the Mojave and western Sonoran Desert routinely used several parts of the Joshua tree as food and fiber (Cornett, J.W., 2018, Indian Uses of Desert Plants, Nature Trails Press, Palm Springs, CA). Leaf fibers were occasionally used to bind and manufacture sandals. Root sheaths were woven into baskets to add reddish-brown designs. Fruits were baked or boiled then eaten. Seeds were ground into flour and mixed with flour from other plant species. The flour
3910-553: The equivalents of the petioles and stipules of leaves. Because each leaflet can appear to be a simple leaf, it is important to recognize where the petiole occurs to identify a compound leaf. Compound leaves are a characteristic of some families of higher plants, such as the Fabaceae . The middle vein of a compound leaf or a frond , when it is present, is called a rachis . Leaves which have a petiole (leaf stalk) are said to be petiolate . Sessile (epetiolate) leaves have no petiole and
3995-657: The external world. The cuticle is in some cases thinner on the lower epidermis than on the upper epidermis, and is generally thicker on leaves from dry climates as compared with those from wet climates. The epidermis serves several functions: protection against water loss by way of transpiration , regulation of gas exchange and secretion of metabolic compounds. Most leaves show dorsoventral anatomy: The upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions. The epidermis tissue includes several differentiated cell types; epidermal cells, epidermal hair cells ( trichomes ), cells in
4080-406: The fraction is 5/13. These arrangements are periodic. The denominator of the rotation fraction indicates the number of leaves in one period, while the numerator indicates the number of complete turns or gyres made in one period. For example: Most divergence angles are related to the sequence of Fibonacci numbers F n . This sequence begins 1, 1, 2, 3, 5, 8, 13; each term is the sum of
4165-478: The geographical reach of the Mojave Desert, where it is considered one of the major indicator species for the desert. It occurs at elevations between 400 and 1,800 m (1,300 and 5,900 ft). Joshua trees are one of the species predicted to have their range reduced and shifted by climate change . Concern remains that they will be eliminated from Joshua Tree National Park, with ecological research suggesting
4250-866: The ground, they are referred to as prostrate . Perennial plants whose leaves are shed annually are said to have deciduous leaves, while leaves that remain through winter are evergreens . Leaves attached to stems by stalks (known as petioles ) are called petiolate, and if attached directly to the stem with no petiole they are called sessile. Dicot leaves have blades with pinnate venation (where major veins diverge from one large mid-vein and have smaller connecting networks between them). Less commonly, dicot leaf blades may have palmate venation (several large veins diverging from petiole to leaf edges). Finally, some exhibit parallel venation. Monocot leaves in temperate climates usually have narrow blades, and usually parallel venation converging at leaf tips or edges. Some also have pinnate venation. The arrangement of leaves on
4335-443: The leaf from the petiole are called primary or first-order veins. The veins branching from these are secondary or second-order veins. These primary and secondary veins are considered major veins or lower order veins, though some authors include third order. Each subsequent branching is sequentially numbered, and these are the higher order veins, each branching being associated with a narrower vein diameter. In parallel veined leaves,
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#17328482273344420-523: The leaf veins form, and these have functional implications. Of these, angiosperms have the greatest diversity. Within these the major veins function as the support and distribution network for leaves and are correlated with leaf shape. For instance, the parallel venation found in most monocots correlates with their elongated leaf shape and wide leaf base, while reticulate venation is seen in simple entire leaves, while digitate leaves typically have venation in which three or more primary veins diverge radially from
4505-551: The leaves of vascular plants . In most cases, they lack vascular tissue, are only a single cell thick, and have no cuticle , stomata, or internal system of intercellular spaces. (The phyllids of the moss family Polytrichaceae are notable exceptions.) The phyllids of bryophytes are only present on the gametophytes , while in contrast the leaves of vascular plants are only present on the sporophytes . These can further develop into either vegetative or reproductive structures. Simple, vascularized leaves ( microphylls ), such as those of
4590-925: The majority, as broad-leaved or megaphyllous plants, which also include acrogymnosperms and ferns . In the lycopods , with different evolutionary origins, the leaves are simple (with only a single vein) 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 often 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 totally homologous with them. Examples include flattened plant stems called phylloclades and cladodes , and flattened leaf stems called phyllodes which differ from leaves both in their structure and origin. Some structures of non-vascular plants look and function much like leaves. Examples include
4675-408: The nearest Joshua tree. If it survives the rigors of the desert, it can live for several hundred years. The tallest trees reach about 15 m (49 ft). New plants can grow from seed , but in some populations, new stems grow from underground rhizomes that spread out around the parent tree. The evergreen leaves are dark green, linear, bayonet-shaped, 15 to 35 cm long, and 7 to 15 mm broad at
4760-956: The north through Baja California in the west, northwards into the southwestern United States , through the drier central states as far north as southern Alberta in Canada ( Yucca glauca ssp. albertana ). Yucca is also native northward to the coastal lowlands and dry beach scrub of the coastal areas of the southeastern United States , along the Gulf of Mexico and South Atlantic States from coastal Texas to Maryland . Yuccas have adapted to an equally vast range of climatic and ecological conditions. They are found in rocky deserts and badlands , in prairies and grassland , in mountainous regions, woodlands, in coastal sands ( Yucca filamentosa ), and even in subtropical and semi temperate zones. Several species occur in humid tropical zones ( Yucca lacandonica ) but most species occur in arid conditions, with
4845-404: 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 (length and width measured in tens of μm) openings called stomata which open or close to regulate
4930-412: The plant and provides the route for transfer of water and sugars to and from the leaf. The lamina is typically the location of the majority of photosynthesis. The upper ( adaxial ) angle between a leaf and a stem is known as the axil of the leaf. It is often the location of a bud . Structures located there are called "axillary". External leaf characteristics, such as shape, margin, hairs, the petiole, and
5015-411: The presence of a compound called chlorophyll which is essential for photosynthesis as it absorbs light energy from the sun . A leaf with lighter-colored or white patches or edges is called a variegated leaf . Leaves can have many different shapes, sizes, textures and colors. The broad, flat leaves with complex venation of flowering plants are known as megaphylls and the species that bear them,
5100-434: The presence of stipules and glands, are frequently important for identifying plants to family, genus or species levels, and botanists have developed a rich terminology for describing leaf characteristics. Leaves almost always have determinate growth. They grow to a specific pattern and shape and then stop. Other plant parts like stems or roots have non-determinate growth, and will usually continue to grow as long as they have
5185-410: The previous two. Rotation fractions are often quotients F n / F n + 2 of a Fibonacci number by the number two terms later in the sequence. This is the case for the fractions 1/2, 1/3, 2/5, 3/8, and 5/13. The ratio between successive Fibonacci numbers tends to the golden ratio φ = (1 + √5)/2 . When a circle is divided into two arcs whose lengths are in the ratio 1:φ , the angle formed by
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#17328482273345270-465: The primary organs responsible for transpiration and guttation (beads of fluid forming at leaf margins). Leaves can also store food and water , and are modified accordingly to meet these functions, for example in the leaves of succulent plants and in bulb scales. The concentration of photosynthetic structures in leaves requires that they be richer in protein , minerals , and sugars than, say, woody stem tissues. Accordingly, leaves are prominent in
5355-429: The primary veins run parallel and equidistant to each other for most of the length of the leaf and then converge or fuse (anastomose) towards the apex. Usually, many smaller minor veins interconnect these primary veins, but may terminate with very fine vein endings in the mesophyll. Minor veins are more typical of angiosperms, which may have as many as four higher orders. In contrast, leaves with reticulate venation have
5440-416: The products of photosynthesis (photosynthate) from the cells where it takes place, while major veins are responsible for its transport outside of the leaf. At the same time water is being transported in the opposite direction. The number of vein endings is very variable, as is whether second order veins end at the margin, or link back to other veins. There are many elaborate variations on the patterns that
5525-429: 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 (each cone scale is a modified megaphyll leaf known as a sporophyll) and from which flowers are constructed in flowering plants . The internal organization of most kinds of leaves has evolved to maximize exposure of
5610-714: The rate exchange of carbon dioxide (CO 2 ), oxygen (O 2 ) and water vapor into and out of the internal intercellular space system. Stomatal opening is controlled by the turgor pressure in a pair of guard cells that surround the stomatal aperture. In any square centimeter of a plant leaf, there may be from 1,000 to 100,000 stomata. The shape and structure of leaves vary considerably from species to species of plant, depending largely on their adaptation to climate and available light, but also to other factors such as grazing animals (such as deer), available nutrients, and ecological competition from other plants. Considerable changes in leaf type occur within species, too, for example as
5695-531: The resources to do so. The type of leaf is usually characteristic of a species (monomorphic), although some species produce more than one type of leaf (dimorphic or polymorphic ). The longest leaves are those of the Raffia palm , R. regalis which may be up to 25 m (82 ft) long and 3 m (9.8 ft) wide. The terminology associated with the description of leaf morphology is presented, in illustrated form, at Wikibooks . Where leaves are basal, and lie on
5780-558: The sap, and are widely used in food, cosmetics, and pharmaceuticals The flower petals are commonly eaten in Central America , but the plant's reproductive organs (the anthers and ovaries ) are first removed because of their bitterness. The petals are blanched for 5 minutes, and then cooked a la mexicana (with tomato, onion, chili) or in tortitas con salsa (egg-battered patties with green or red sauce). In Guatemala , they are boiled and eaten with lemon juice. In El Salvador ,
5865-446: The secondary veins, known as tertiary or third order (or higher order) veins, forming a dense reticulate pattern. The areas or islands of mesophyll lying between the higher order veins, are called areoles . Some of the smallest veins (veinlets) may have their endings in the areoles, a process known as areolation. These minor veins act as the sites of exchange between the mesophyll and the plant's vascular system. Thus, minor veins collect
5950-455: The sequence 180°, 90°, 180°, 270°. Two basic forms of leaves can be described considering the way the blade (lamina) is divided. A simple leaf has an undivided blade. However, the leaf may be dissected to form lobes, but the gaps between lobes do not reach to the main vein. A compound leaf has a fully subdivided blade, each leaflet of the blade being separated along a main or secondary vein. The leaflets may have petiolules and stipels,
6035-454: The smaller arc is the golden angle , which is 1/φ × 360° ≈ 137.5° . Because of this, many divergence angles are approximately 137.5° . In plants where a pair of opposite leaves grows from each node, the leaves form a double helix. If the nodes do not rotate (a rotation fraction of zero and a divergence angle of 0°), the two helices become a pair of parallel lines, creating a distichous arrangement as in maple or olive trees. More common in
6120-486: The species. Certain species of the yucca moth have evolved antagonistic features against the plant. They do not assist in the plant's pollination efforts while continuing to lay their eggs in the plant for protection. Yucca species are the host plants for the caterpillars of the yucca giant-skipper ( Megathymus yuccae ), ursine giant-skipper ( Megathymus ursus ), and Strecker's giant-skipper ( Megathymus streckeri ). Beetle herbivores include yucca weevils , in
6205-421: The stem is known as phyllotaxis . A large variety of phyllotactic patterns occur in nature: In the simplest mathematical models of phyllotaxis , the apex of the stem is represented as a circle. Each new node is formed at the apex, and it is rotated by a constant angle from the previous node. This angle is called the divergence angle . The number of leaves that grow from a node depends on the plant species. When
6290-421: The stigma cavity is surrounded by lobes. The semi-fleshy fruit that is produced is green-brown, elliptical, and contains many flat seeds. Joshua trees usually do not branch until after they bloom (though branching may also occur if the growing tip is destroyed by the yucca-boring weevil ), and they do not bloom every year. Like most desert plants, their blooming depends on rainfall at the proper time. They also need
6375-547: The stomatal complex; guard cells and subsidiary cells. The epidermal cells are the most numerous, largest, and least specialized and form the majority of the epidermis. They are typically more elongated in the leaves of monocots than in those of dicots . Chloroplasts are generally absent in epidermal cells, the exception being the guard cells of the stomata . The stomatal pores perforate the epidermis and are surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts, forming
6460-511: 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, and guttation . Many conifers 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
6545-594: The tender tips of stems are eaten and known locally as cogollo de izote . The most common houseplant yucca is Yucca gigantea . Yuccas are widely grown as architectural plants providing a dramatic accent to landscape design. They tolerate a range of conditions but are best grown in full sun in subtropical or mild temperate areas. In gardening centres and horticultural catalogues, they are usually grouped with other architectural plants such as cordylines and phormiums . Several species of yucca can be grown outdoors in temperate climates, including:- The yucca flower
6630-485: The tough, fibrous leaves were used to puncture meat and knotted to form a loop with which to hang meat for salt curing or in smokehouses. The fibers can be used to make domestic items or for manufacturing cordage, be it sewing-thread or rope. Yucca extract is also used as a foaming agent in some beverages such as root beer and soda. Yucca powder and sap are derived from the logs of the plant; such extracts can be produced by mechanical squeezing and subsequent evaporation of
6715-632: The transportation system. Typically leaves are broad, flat and thin (dorsiventrally flattened), 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 eucalypts . The flat, or laminar, shape also maximizes thermal contact with
6800-559: The trees' dispersal. However, ground squirrels are very effective at moving the seeds long distances. In March 2022, California Department of Fish and Wildlife conducted a status review of the Western Joshua Tree to determine whether to list the species as threatened under the California Endangered Species Act (CESA). The study showed that the largest threat to Yucca brevifolia was wildfires, that wildfires were
6885-462: The vascular structure of the organ, extending into the leaf via the petiole and providing transportation of water and nutrients between leaf and stem, and play a crucial role in the maintenance of leaf water status and photosynthetic capacity. They also play a role in the mechanical support of the leaf. Within the lamina of the leaf, while some vascular plants possess only a single vein, in most this vasculature generally divides (ramifies) according to
6970-577: The world in Mojave National Preserve were killed in the Dome Fire in August 2020. Also, concern exists about the ability of the species to migrate to favorable climates due to the extinction of the giant Shasta ground sloth ( Nothrotheriops shastensis ) 13,000 years ago; ground sloth dung has been found to contain Joshua tree leaves, fruits, and seeds, suggesting that the sloths might have been key to
7055-502: Was first formally described in the botanical literature as Yucca brevifolia by George Engelmann in 1871 as part of the Geological Exploration of the 100th meridian (or " Wheeler Survey "). The name "Joshua tree" is commonly said to have been given by a group of Mormon settlers crossing the Mojave Desert in the mid-19th century: The tree's role in guiding them through the desert combined with its unique shape reminded them of
7140-399: Was moistened with water and the resulting paste was kneaded into cakes and dried. Yucca See text Yucca is a genus of perennial shrubs and trees in the family Asparagaceae , subfamily Agavoideae . Its 40–50 species are notable for their rosettes of evergreen , tough, sword-shaped leaves and large terminal panicles of white or whitish flowers . They are native to
7225-479: Was noted in the review. The review concluded: Based on the criteria described above, the best scientific information available to the Department at this time indicates that western Joshua tree is not in serious danger of becoming extinct throughout all, or a significant portion, of its range due to one or more causes, including loss of habitat, change in habitat, overexploitation, predation, competition, or disease, and
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