Plant reproductive morphology is the study of the physical form and structure (the morphology ) of those parts of plants directly or indirectly concerned with sexual reproduction .
36-423: 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
72-800: 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
108-443: 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
144-528: A four-celled ovary. Since only female plants are able to set fruit and produce berries, this has consequences for gardeners. Amborella represents the first known group of flowering plants to separate from their common ancestor. It too is dioecious; at any one time, each plant produces either flowers with functional stamens but no carpels, or flowers with a few non-functional stamens and a number of fully functional carpels. However, Amborella plants may change their "sex" over time. In one study, five cuttings from
180-401: A male plant produced only male flowers when they first flowered, but at their second flowering three switched to producing female flowers. In extreme cases, almost all of the parts present in a complete flower may be missing, so long as at least one carpel or one stamen is present. This situation is reached in the female flowers of duckweeds ( Lemna ), which consist of a single carpel, and in
216-441: A perianth. (See the illustration of Alnus serrulata .) Most hollies (members of the genus Ilex ) are dioecious. Each plant produces either functionally male flowers or functionally female flowers. In Ilex aquifolium (see the illustration), the common European holly, both kinds of flower have four sepals and four white petals; male flowers have four stamens, female flowers usually have four non-functional reduced stamens and
252-647: 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
288-421: 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 )
324-766: 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
360-514: Is a tiny female gametophyte. Carpels may be called the "female" parts of a flower and collectively form the gynoecium. Each carpel in Ranunculus species is an achene that produces one ovule, which when fertilized becomes a seed. If the carpel contains more than one seed, as in Eranthis hyemalis , it is called a follicle . Two or more carpels may be fused together to varying degrees and
396-535: 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
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#1732772552866432-480: The coevolution of flowers and their insect pollinators . Plants have complex lifecycles involving alternation of generations . One generation, the sporophyte , gives rise to the next generation, the gametophyte asexually via spores . Spores may be identical isospores or come in different sizes ( microspores and megaspores ), but strictly speaking, spores and sporophytes are neither male nor female because they do not produce gametes . The alternate generation,
468-538: The sperm from one plant fertilizes the ovum of another, depends on the reproductive morphology, and is the single most important determinant of the genetic structure of nonclonal plant populations. Christian Konrad Sprengel (1793) studied the reproduction of flowering plants and for the first time it was understood that the pollination process involved both biotic and abiotic interactions. Charles Darwin 's theories of natural selection utilized this work to build his theory of evolution , which includes analysis of
504-770: 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
540-466: 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
576-506: 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. Plant reproductive morphology#Variations Among all living organisms, flowers , which are
612-431: The carpels are missing, vestigial or otherwise non-functional. Each flower is either staminate (having only functional stamens and thus male), or carpellate or pistillate (having only functional carpels and thus female). If separate staminate and carpellate flowers are always found on the same plant, the species is described as monoecious . If separate staminate and carpellate flowers are always found on different plants,
648-475: The carpels mature first). Monoecious species, with unisexual flowers on the same plant, may produce male and female flowers at different times. Dioecy, the condition of having unisexual flowers on different plants, necessarily results in outcrossing, and probably evolved for this purpose. However, "dioecy has proven difficult to explain simply as an outbreeding mechanism in plants that lack self-incompatibility". Resource-allocation constraints may be important in
684-413: The entire structure, including the fused styles and stigmas may be called a pistil . The lower part of the pistil, where the ovules are produced, is called the ovary . It may be divided into chambers ( locules ) corresponding to the separate carpels. A perfect flower has both stamens and carpels, and is described as "bisexual" or "hermaphroditic". A unisexual flower is one in which either the stamens or
720-448: The evolution of dioecy, for example, with wind-pollination, separate male flowers arranged in a catkin that vibrates in the wind may provide better pollen dispersal. In climbing plants, rapid upward growth may be essential, and resource allocation to fruit production may be incompatible with rapid growth, thus giving an advantage to delayed production of female flowers. Dioecy has evolved separately in many different lineages, and monoecy in
756-492: The figure, has a calyx of outer sepals and a corolla of inner petals and both male and female sex organs . The sepals and petals together form the perianth . Next inwards there are numerous stamens , which produce pollen grains, each containing a microscopic male gametophyte. Stamens may be called the "male" parts of a flower and collectively form the androecium. Finally in the middle there are carpels , which at maturity contain one or more ovules , and within each ovule
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#1732772552866792-421: The gametophyte, produces gametes, eggs and/or sperm . A gametophyte can be monoicous (bisexual), producing both eggs and sperm, or dioicous (unisexual), either female (producing eggs) or male (producing sperm). In the bryophytes ( liverworts , mosses , and hornworts ), the sexual gametophyte is the dominant generation. In ferns and seed plants (including cycads , conifers , flowering plants , etc.)
828-466: 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
864-473: The male flowers of spurges ( Euphorbia ) which consist of a single stamen. A species such as Fraxinus excelsior , the common ash of Europe, demonstrates one possible kind of variation. Ash flowers are wind-pollinated and lack petals and sepals. Structurally, the flowers may be bisexual, consisting of two stamens and an ovary, or may be male (staminate), lacking a functional ovary, or female (carpellate), lacking functional stamens. Different forms may occur on
900-406: The masking of deleterious recessive mutations. The primary mechanism used by flowering plants to ensure outcrossing involves a genetic mechanism known as self-incompatibility . Various aspects of floral morphology promote allogamy. In plants with bisexual flowers, the anthers and carpels may mature at different times, plants being protandrous (with the anthers maturing first) or protogynous (with
936-420: The protective wall of a pollen grain. The sporophyte of a flowering plant is often described using sexual terms (e.g. "female" or "male") based on the sexuality of the gametophyte it gives rise to . For example, a sporophyte that produces spores that give rise only to male gametophytes may be described as "male", even though the sporophyte itself is asexual, producing only spores. Similarly, flowers produced by
972-430: The reproductive structures of angiosperms , are the most varied physically and show a correspondingly great diversity in methods of reproduction. Plants that are not flowering plants ( green algae , mosses , liverworts , hornworts , ferns and gymnosperms such as conifers ) also have complex interplays between morphological adaptation and environmental factors in their sexual reproduction. The breeding system, or how
1008-519: The same tree, or on different trees. The Asteraceae (sunflower family), with close to 22,000 species worldwide, have highly modified inflorescences made up of flowers (florets) collected together into tightly packed heads. Heads may have florets of one sexual morphology – all bisexual, all carpellate or all staminate (when they are called homogamous ), or may have mixtures of two or more sexual forms (heterogamous). Thus goatsbeards ( Tragopogon species) have heads of bisexual florets, like other members of
1044-469: The species is described as dioecious . A 1995 study found that about 6% of angiosperm species are dioecious, and that 7% of genera contain some dioecious species. Members of the birch family ( Betulaceae ) are examples of monoecious plants with unisexual flowers. A mature alder tree ( Alnus species) produces long catkins containing only male flowers, each with four stamens and a minute perianth, and separate stalked groups of female flowers, each without
1080-489: The sporophyte is the dominant generation; the obvious visible plant, whether a small herb or a large tree, is the sporophyte, and the gametophyte is very small. In bryophytes and ferns, the gametophytes are independent, free-living plants, while in seed plants, each female megagametophyte, and the megaspore that gives rise to it, is hidden within the sporophyte and is entirely dependent on it for nutrition. Each male gametophyte typically consists of two to four cells enclosed within
1116-401: The sporophyte may be described as "unisexual" or "bisexual", meaning that they give rise to either one sex of gametophyte or both sexes of the gametophyte. The flower is the characteristic structure concerned with sexual reproduction in flowering plants (angiosperms). Flowers vary enormously in their structure (morphology). A perfect flower, like that of Ranunculus glaberrimus shown in
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1152-409: The tribe Cichorieae, whereas marigolds ( Calendula species) generally have heads with the outer florets bisexual and the inner florets staminate (male). Like Amborella , some plants undergo sex-switching. For example, Arisaema triphyllum (Jack-in-the-pulpit) expresses sexual differences at different stages of growth: smaller plants produce all or mostly male flowers; as plants grow larger over
1188-928: The year and as plants bloom later in the growing season they produce more female flowers. The complexity of the morphology of flowers and its variation within populations has led to a rich terminology. Outcrossing , cross-fertilization or allogamy, in which offspring are formed by the fusion of the gametes of two different plants, is the most common mode of reproduction among higher plants . About 55% of higher plant species reproduce in this way. An additional 7% are partially cross-fertilizing and partially self-fertilizing (autogamy). About 15% produce gametes but are principally self-fertilizing with significant out-crossing lacking. Only about 8% of higher plant species reproduce exclusively by non-sexual means. These include plants that reproduce vegetatively by runners or bulbils, or which produce seeds without embryo fertilization ( apomixis ). The selective advantage of outcrossing appears to be
1224-409: The years the male flowers are replaced by more female flowers on the same plant. Arisaema triphyllum thus covers a multitude of sexual conditions in its lifetime: nonsexual juvenile plants, young plants that are all male, larger plants with a mix of both male and female flowers, and large plants that have mostly female flowers. Other plant populations have plants that produce more male flowers early in
1260-413: 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
1296-624: 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
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