Misplaced Pages

#195804

27-423: The white oaks are species of trees in the genus Quercus section Quercus . White oak , White Oak or Whiteoak may also refer to: Quercus sect. Quercus Quercus subgenus Quercus is one of the two subgenera into which the genus Quercus was divided in a 2017 classification (the other being subgenus Cerris ). It contains about 190 species divided among five sections . It may be called

54-793: A characteristic flange-like shape. The staminate flowers have up to six stamens . The stalk connecting the perianth to the ovary is cone-shaped and often has rings. The acorns mature in two years, rarely in one year. The 'cup' (cupule) of the acorn is fused with its stalk ( peduncule ) forming a connective piece. Both the connective piece and the cup are covered with small triangular scales, mostly thin and membranous with broadly angled tips. The leaves typically have teeth with bristle-like extensions, or just bristles in leaves without teeth. The section contains about 125 species native to Northern America (including Mexico ), Central America , and Colombia in South America. The red oaks of Mexico are one of

81-443: A cup covers at least the base of the nut. The outer structure of the mature pollen is one feature that distinguishes the two subgenera: in subgenus Quercus , the small folds or wrinkles (rugulae) are obscured by sporopollenin , whereas in subgenus Cerris , the rugulae are visible or at most weakly obscured. The two subgenera are also distinguished to some extent by their different distributions. Subgenus Quercus occurs mainly in

108-409: A few species of Trithuria (family Hydatellaceae ) are exceptional in that their gynoecia surround their androecia. Depending on the species of plant, some or all of the stamens in a flower may be attached to the petals or to the floral axis . They also may be free-standing or fused to one another in many different ways, including fusion of some but not all stamens. The filaments may be fused and

135-647: A section by Otto Karl Anton Schwarz in 1936 and Aimée Antoinette Camus in 1938. The staminate flowers have eight to ten stamens . The pollen ornamentation has only small wrinkles or folds (verrucae). The acorns mature after two years. The cup (cupule) at the base of the acorn has triangular scales that are fused at the base and have sharp angled tips. The scales are thick and compressed into rings, often forming small bumps, that may be obscured by glandular hairs. The leaf teeth end in spines. The section contains only five species, native to southwestern North America and northwestern Mexico. Quercus sect. Ponticae

162-497: A single locule ) as in Canna species or as many as 3,482 stamens which have been counted in the saguaro ( Carnegiea gigantea ). The androecium in various species of plants forms a great variety of patterns, some of them highly complex. It generally surrounds the gynoecium and is surrounded by the perianth . A few members of the family Triuridaceae , particularly Lacandonia schismatica and Lacandonia brasiliana , along with

189-416: A stalk called the filament and an anther which contains microsporangia . Most commonly anthers are two-lobed (each lobe is termed a locule ) and are attached to the filament either at the base or in the middle area of the anther. The sterile tissue between the lobes is called the connective , an extension of the filament containing conducting strands. It can be seen as an extension on the dorsal side of

216-421: A year. The cup at the base of the acorn has narrowly triangular scales, with thin keels, at most small bumps (tubercules), and sharp angled ends. The leaves are evergreen or almost so. A distinctive feature of the section is that the germinating seed has fused seed leaves ( cotyledons ) and an elongated stem above the cotyledons (the epicotyl ) that forms a tube, while the stem below the cotyledons (the hypocotyl )

243-760: Is tuberous . The section contains seven species, native to south-eastern Northern America, Mexico, the West Indies ( Cuba ), and Central America. Quercus sect. Quercus has been known, either in whole or part, by a variety of names in the past, including Quercus  sect.  Albae , Quercus  sect.  Macrocarpae and Quercus  sect.  Mesobalanus . Members of the section may be called white oaks. The section includes all white oaks from North America (treated by Trelease as subgenus Leucobalanus ). The staminate flowers have seven or more stamens . The acorns mature in one year. The seed leaves ( cotyledons ) are either free or fused together. The cup at

270-458: Is called appendiculate , e.g. Nerium odorum and some other species of Apocynaceae . In Nerium , the appendages are united as a staminal corona. A column formed from the fusion of multiple filaments is known as an androphore . Stamens can be connate (fused or joined in the same whorl) as follows: Anther shapes are variously described by terms such as linear , rounded , sagittate , sinuous , or reniform . The anther can be attached to

297-458: Is called a staminate flower , or (inaccurately) a male flower. A flower with a functional pistil but no functional stamens is called a pistillate flower , or (inaccurately) a female flower. An abortive or rudimentary stamen is called a staminodium or staminode , such as in Scrophularia nodosa . The carpels and stamens of orchids are fused into a column . The top part of the column

SECTION 10

#1732845382196

324-410: Is formed by the anther, which is covered by an anther cap . Stamens can also be adnate (fused or joined from more than one whorl): They can have different lengths from each other: or respective to the rest of the flower ( perianth ): They may be arranged in one of two different patterns: They may be arranged, with respect to the petals : Where the connective is very small, or imperceptible,

351-528: Is native to mountainous areas of north-eastern Turkey and western Georgia . Quercus sadleriana is native to northern-most California and southern-most Oregon in the United States. Quercus sect. Virentes was first established by John Claudius Loudon in 1838. It has also been treated as a series. Members of the section may be called live oaks. Species are trees or rhizomatous shrubs. They are evergreen or brevideciduous . The acorns mature in

378-488: The heath family ( Ericaceae ), or by valves, as in the barberry family ( Berberidaceae ). In some plants, notably members of Orchidaceae and Asclepiadoideae , the pollen remains in masses called pollinia , which are adapted to attach to particular pollinating agents such as birds or insects. More commonly, mature pollen grains separate and are dispensed by wind or water, pollinating insects, birds or other pollination vectors. Pollen of angiosperms must be transported to

405-443: The stigma , the receptive surface of the carpel , of a compatible flower, for successful pollination to occur. After arriving, the pollen grain (an immature microgametophyte) typically completes its development. It may grow a pollen tube and undergo mitosis to produce two sperm nuclei. In the typical flower (that is, in the majority of flowering plant species) each flower has both carpels and stamens . In some species, however,

432-437: The tapetum and initially contains diploid pollen mother cells. These undergo meiosis to form haploid spores. The spores may remain attached to each other in a tetrad or separate after meiosis. Each microspore then divides mitotically to form an immature microgametophyte called a pollen grain . The pollen is eventually released when the anther forms openings ( dehisces ). These may consist of longitudinal slits, pores, as in

459-749: The Americas, with some species native to Eurasia and North Africa , and may be called the New World clade or the high-latitude clade. Subgenus Cerris is primarily Eurasian, with a few species in North Africa, and may be called the Old World clade or the mid-latitude clade. The following cladogram summarizes the relationships that Denk et al. used to draw up their 2017 classification: sect. Lobatae sect. Protobalanus sect. Ponticae sect. Virentes sect. Quercus subg. Cerris Quercus sect. Lobatae

486-461: The New World clade or the high-latitude clade; most species are native to the Americas, the others being found in Eurasia and northernmost North Africa . Members of subgenus Quercus are distinguished from members of subgenus Cerris by few morphological features, their separation being largely determined by molecular phylogenetic evidence. All are trees or shrubs bearing acorn -like fruit in which

513-425: The anther lobes are close together, and the connective is referred to as discrete , e.g. Euphorbia pp., Adhatoda zeylanica . Where the connective separates the anther lobes, it is called divaricate , e.g. Tilia , Justicia gendarussa . The connective may also be a long and stalk-like, crosswise on the filament, this is a distractile connective, e.g. Salvia . The connective may also bear appendages, and

540-518: The anther. A pollen grain develops from a microspore in the microsporangium and contains the male gametophyte . The size of anthers differs greatly, from a tiny fraction of a millimeter in Wolfia spp up to five inches (13 centimeters) in Canna iridiflora and Strelitzia nicolai . The stamens in a flower are collectively called the androecium . The androecium can consist of as few as one-half stamen (i.e.

567-419: The anthers free, or the filaments free and the anthers fused. Rather than there being two locules, one locule of a stamen may fail to develop, or alternatively the two locules may merge late in development to give a single locule. Extreme cases of stamen fusion occur in some species of Cyclanthera in the family Cucurbitaceae and in section Cyclanthera of genus Phyllanthus (family Euphorbiaceae ) where

SECTION 20

#1732845382196

594-460: The base of the acorn has thickened triangular scales that are either free or fused at the base and have sharp angled tips. The scales have keels and are often covered with small bumps (tuberculate). The leaf teeth typically do not have either bristle-like or spiny tips. There are about 150 species, native to Northern America, Mexico, Central America, western Eurasia , East Asia, and North Africa. Stamen A stamen typically consists of

621-400: The flowers are unisexual with only carpels or stamens. ( monoecious = both types of flowers found on the same plant; dioecious = the two types of flower found only on different plants). A flower with only stamens is called androecious . A flower with only carpels is called gynoecious . A pistil consists of one or more carpels. A flower with functional stamens but no functional pistil

648-462: The groups of oaks that have most rapidly diversified into different species. Molecular evidence suggests that there are significant numbers of undescribed Quercus species in Mexico, so the number of known species in the section is likely to be an underestimate of the total diversity. Quercus sect. Protobalanus was first established as a subgenus by William Trelease in 1922 and then later treated as

675-427: The stamens form a ring around the gynoecium, with a single locule. Plants having a single stamen are referred to as "monandrous." A typical anther contains four microsporangia. The microsporangia form sacs or pockets ( locules ) in the anther (anther sacs or pollen sacs). The two separate locules on each side of an anther may fuse into a single locule. Each microsporangium is lined with a nutritive tissue layer called

702-413: Was established by John Claudius Loudon in 1830. The section, or part of it, has also been treated under names including Quercus sect. Rubrae Loudon and Quercus sect. Erythrobalanus Spach . It has also been treated as the subgenus Erythrobalanus and as the full genus Erythrobalanus (Spach) O.Schwarz . Its members may be called red oaks. The perianth of the pistillate flowers has

729-624: Was first established by Boris Stefanoff in 1930. It has also been treated as a subsection and a series, including under the name Q. ser. Sadlerianae Trelease . Species are shrubs or small trees, with rhizomes . The staminate catkins are up to 10 cm long. The cup (cupule) at the base of the acorn has scales with sharp angled ends. The leaves are either evergreen or deciduous, with simple or compound teeth. The leaf buds are large, enclosed in loosely attached scales. There are only two species, Quercus pontica and Quercus sadleriana . They have disjoint distributions. Quercus pontica

#195804