In biology , a monotypic taxon is a taxonomic group ( taxon ) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera , the term "unispecific" or "monospecific" is sometimes preferred. In botanical nomenclature , a monotypic genus is a genus in the special case where a genus and a single species are simultaneously described.
56-446: Amborella is a monotypic genus of understory shrubs or small trees endemic to the main island, Grande Terre , of New Caledonia in the southwest Pacific Ocean. The genus is the only member of the family Amborellaceae and the order Amborellales and contains a single species , Amborella trichopoda . Amborella is of great interest to plant systematists because molecular phylogenetic analyses consistently place it as
112-602: A common ancestor ) or paraphyletic (excluding some descendants), these concepts do not apply to monotypic taxa because they contain only a single member. Monotypic taxa are part of a broader challenge in biological classification known as aphyly – situations where evolutionary relationships are poorly supported by evidence. This includes both monotypic groups and cases where traditional groupings are found to be artificial. Understanding how monotypic taxa fit into this bigger picture helps identify areas needing further research. The German lichenologist Robert Lücking suggests that
168-482: A hierarchical system. When taxonomists identify a monotypic taxon, this often reflects uncertainty about its relationships rather than true evolutionary isolation . This uncertainty is evident in many cases across different species. For instance, the diatom Licmophora juergensii is placed in a monotypic genus because scientists have not yet found clear evidence of its relationships to other species. Some taxonomists argue against monotypic taxa because they reduce
224-419: A primitive feature of flowering plants. The species is dioecious . This means that each plant produces either male flowers (meaning that they have functional stamens ) or female flowers (flowers with functional carpels ), but not both. At any one time, a dioecious plant produces only functionally staminate or functionally carpellate flowers. Staminate ("male") Amborella flowers do not have carpels, whereas
280-409: A broad stigmatic crest along the margin allows pollen tubes access along the surface and between hairs at the margins. Two kinds of fusion have been distinguished: postgenital fusion that can be observed during the development of flowers, and congenital fusion that cannot be observed i.e., fusions that occurred during phylogeny. But it is very difficult to distinguish fusion and non-fusion processes in
336-400: A conical or dome-shaped receptacle . In later lineages, carpels tend to be in whorls . The relationship of the other flower parts to the gynoecium can be an important systematic and taxonomic character. In some flowers, the stamens, petals, and sepals are often said to be "fused" into a "floral tube" or hypanthium . However, as Leins & Erbar (2010) pointed out, "the classical view that
392-428: A family. Some examples of monotypic groups are: Gynoecium Gynoecium ( / ɡ aɪ ˈ n iː s i . ə m , dʒ ɪ ˈ n iː ʃ i . ə m / ; from Ancient Greek γυνή ( gunḗ ) 'woman, female' and οἶκος ( oîkos ) 'house'; pl. : gynoecia ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into
448-421: A hypanthium is present, but is either free from the gynoecium (in which case it may appear to be a cup or tube surrounding the gynoecium) or connected partly to the gynoecium (with the stamens, petals, and sepals attached to the hypanthium part of the way up the ovary). Perigynous flowers are often referred to as having a half-inferior ovary (or, sometimes, partially inferior or half-superior ). This arrangement
504-577: A male flower is referred to as a pistillode . The pistils of a flower are considered to be composed of one or more carpels . A carpel is the female reproductive part of the flower—usually composed of the style , and stigma (sometimes having its individual ovary , and sometimes connecting to a shared basal ovary) —and usually interpreted as modified leaves that bear structures called ovules , inside which egg cells ultimately form. A pistil may consist of one carpel (with its ovary, style and stigma); or it may comprise several carpels joined together to form
560-418: A monocarpous gynoecium. The degree of connation ("fusion") in a syncarpous gynoecium can vary. The carpels may be "fused" only at their bases, but retain separate styles and stigmas. The carpels may be "fused" entirely, except for retaining separate stigmas. Sometimes (e.g., Apocynaceae ) carpels are fused by their styles or stigmas but possess distinct ovaries. In a syncarpous gynoecium, the "fused" ovaries of
616-553: A natural classification. From a cladistic perspective, which focuses on shared derived characteristics to determine evolutionary relationships, the theoretical status of monotypic taxa is complex. Some argue they can only be justified when relationships cannot be resolved through synapomorphies (shared derived characteristics); otherwise, they would necessarily exclude related species and thus be paraphyletic. However, others contend that while most taxonomic groups can be classified as either monophyletic (containing all descendants of
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#1732793043076672-460: A similar function to a megasporophyll , but typically includes a stigma, and is fused, with ovules enclosed in the enlarged lower portion, the ovary. In some basal angiosperm lineages, Degeneriaceae and Winteraceae , a carpel begins as a shallow cup where the ovules develop with laminar placentation, on the upper surface of the carpel. The carpel eventually forms a folded, leaf-like structure, not fully sealed at its margins. No style exists, but
728-404: A single ovary, the whole unit called a pistil. The gynoecium may present as one or more uni-carpellate pistils or as one multi-carpellate pistil. (The number of carpels is denoted by terms such as tricarpellate (three carpels).) Carpels are thought to be phylogenetically derived from ovule-bearing leaves or leaf homologues ( megasporophylls ), which evolved to form a closed structure containing
784-501: A single style and stigma and a single locule in the ovary, it may be necessary to examine how the ovules are attached. Each carpel will usually have a distinct line of placentation where the ovules are attached. Pistils begin as small primordia on a floral apical meristem, forming later than, and closer to the (floral) apex than sepal, petal and stamen primordia. Morphological and molecular studies of pistil ontogeny reveal that carpels are most likely homologous to leaves. A carpel has
840-443: A small sterile central connective. The anthers have connective tips with small bumps and may be covered with secretions. These features suggest that, as with other basal angiosperms , there is a high degree of developmental plasticity. Typically, 1 to 3 carpels per flower develop into fruit. The fruit is an ovoid red drupe (approximately 5 to 7 mm long and 5 mm wide) borne on a short (1 to 2 mm) stalk. The remains of
896-540: A spiral of 4 to 8 free ( apocarpous ) carpels. Carpels bear green ovaries; they lack a style . They contain a single ovule with the micropyle directed downwards. Staminate flowers are approximately 4 to 5 mm in diameter, with 6 to 15 tepals. These flowers bear 10 to 21 spirally arranged stamens, which become progressively smaller toward the center. The innermost may be sterile, amounting to staminodes. The stamens bear triangular anthers on short broad filaments. An anther consists of four pollen sacs, two on each side, with
952-400: A stalked, integumented megasporangium (also called the nucellus ). Typically, one cell in the megasporangium undergoes meiosis resulting in one to four megaspores. These develop into a megagametophyte (often called the embryo sac) within the ovule. The megagametophyte typically develops a small number of cells, including two special cells, an egg cell and a binucleate central cell, which are
1008-423: A unitary intercalary meristem. Evolutionary developmental biology investigates such developmental processes that arise or change during evolution. If the hypanthium is absent, the flower is hypogynous , and the stamens, petals, and sepals are all attached to the receptacle below the gynoecium. Hypogynous flowers are often referred to as having a superior ovary . This is the typical arrangement in most flowers. If
1064-852: Is but one. This preservation has been ascribed to climate stability during and since the Tertiary ( 66 to 3 million years ago ), stability that has permitted the continued survival of tropical forests on New Caledonia. In contrast, drought conditions dominated the Australian climate towards the end of the Tertiary. Current threats to biodiversity in New Caledonia include fires, mining, agriculture, invasion by introduced species, urbanization and global warming. The importance of conserving Amborella has been dramatically stated by Pillon: "The disappearance of Amborella trichopoda would imply
1120-546: Is called the funiculus. Stigmas can vary from long and slender to globe-shaped to feathery. The stigma is the receptive tip of the carpel(s), which receives pollen at pollination and on which the pollen grain germinates . The stigma is adapted to catch and trap pollen, either by combining pollen of visiting insects or by various hairs, flaps, or sculpturings. The style and stigma of the flower are involved in most types of self incompatibility reactions. Self-incompatibility, if present, prevents fertilization by pollen from
1176-438: Is it clear whether the horizontal gene transfer has anything to do with the apparent stability and conservatism of the species. Amborella is typically dioecious, but has been known to change sex in cultivation. Amborella has a mixed pollination system, relying on both insect pollinators and wind. The islands of New Caledonia are a biodiversity hot-spot, preserving many early diverging lineages of plants, of which Amborella
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#17327930430761232-402: Is known as "Gregg's Paradox": if a single species is the only member of multiple hierarchical levels (for example, being the only species in its genus, which is the only genus in its family), then each level needs a distinct definition to maintain logical structure. Otherwise, the different taxonomic ranks become effectively identical, which creates problems for organizing biological diversity in
1288-457: Is not surprising in principle, but the scale of such transfer has caused considerable surprise. Sequencing the Amborella mitochondrial genome revealed that for every gene of its own origin, it contains about six versions from the genomes of an assortment of the plants and algae growing with or upon it. The evolutionary and physiological significance of this is not as yet clear, nor in particular
1344-407: Is particularly associated with island species. Among 25 documented extinct monotypic genera studied, 22 occurred on islands, with flightless animals being particularly vulnerable to human impacts. Just as the term monotypic is used to describe a taxon including only one subdivision, the contained taxon can also be referred to as monotypic within the higher-level taxon, e.g. a genus monotypic within
1400-522: Is particularly frequent in the rose family and saxifrages . Occasionally, the gynoecium is born on a stalk, called the gynophore , as in Isomeris arborea . Within the ovary, each ovule is born by a placenta or arises as a continuation of the floral apex. The placentas often occur in distinct lines called lines of placentation . In monocarpous or apocarpous gynoecia, there is typically a single line of placentation in each ovary. In syncarpous gynoecia,
1456-495: Is that the Amborellaceae alone are the monophyletic sister to the extant angiosperms; another proposes that the Amborellaceae and Nymphaeales form a clade that is the sister group to all other extant angiosperms. Because of its evolutionary position at the base of the flowering plant clade, there was support for sequencing the complete genome of Amborella trichopoda to serve as a reference for evolutionary studies. In 2010,
1512-425: Is the only genus in the family Amborellaceae. The APG II system recognized this family, but left it unplaced at order rank due to uncertainty about its relationship to the family Nymphaeaceae . In the more recent APG systems, APG III and APG IV , the Amborellaceae comprise the monotypic order Amborellales at the base of the angiosperm phylogeny . Currently plant systematists accept Amborella trichopoda as
1568-558: The axils of foliage leaves. The inflorescences have been described as cymes , with up to three orders of branching, each branch being terminated by a flower. Each flower is subtended by bracts . The bracts transition into a perianth of undifferentiated tepals . The tepals typically are arranged in a spiral, but sometimes are whorled at the periphery. Carpellate flowers are roughly 3 to 4 millimetres ( 1 ⁄ 8 to 3 ⁄ 16 in) in diameter, with 7 or 8 tepals. There are 1 to 3 (or rarely 0) well-differentiated staminodes and
1624-400: The fruit and seeds . The gynoecium is the innermost whorl of a flower; it consists of (one or more) pistils and is typically surrounded by the pollen -producing reproductive organs , the stamens , collectively called the androecium . The gynoecium is often referred to as the " female " portion of the flower, although rather than directly producing female gametes (i.e. egg cells ),
1680-409: The gametes involved in double fertilization . The central cell, once fertilized by a sperm cell from the pollen becomes the first cell of the endosperm , and the egg cell once fertilized become the zygote that develops into the embryo . The gap in the integuments through which the pollen tube enters to deliver sperm to the egg is called the micropyle . The stalk attaching the ovule to the placenta
1736-634: The sister group to all other flowering plants , meaning it was the earliest group to evolve separately from all other flowering plants. Amborella is a sprawling shrub or small tree up to 8 metres (26 feet) high. It bears alternate , simple evergreen leaves without stipules . The leaves are two-ranked, with distinctly serrated or rippled margins, and about 8 to 10 centimetres (3 to 4 inches) long. Amborella has xylem tissue that differs from that of most other flowering plants . The xylem of Amborella contains only tracheids ; vessel elements are absent. Xylem of this form has long been regarded as
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1792-405: The stigma can be seen at the tip of the fruit. The skin is papery, surrounding a thin fleshy layer containing a red juice. The inner pericarp is lignified and surrounds the single seed . The embryo is small and surrounded by copious endosperm. The Cronquist system , of 1981, classified the family: The Thorne system (1992) classified it: The Dahlgren system classified it: Amborella
1848-616: The US National Science Foundation began a genome sequencing effort in Amborella , and the draft genome sequence was posted on the project website in December 2013. Amborella is of great interest to plant systematists because molecular phylogenetic analyses consistently place it at or near the base of the flowering plant lineage. That is, the Amborellaceae represent a line of flowering plants that diverged very early on (more than 130 million years ago) from all
1904-465: The androecium. Flowers that bear a gynoecium but no stamens are called pistillate or carpellate . Flowers lacking a gynoecium are called staminate. The gynoecium is often referred to as female because it gives rise to female (egg-producing) gametophytes; however, strictly speaking sporophytes do not have a sex, only gametophytes do. Gynoecium development and arrangement is important in systematic research and identification of angiosperms , but can be
1960-399: The basal angiosperms Amborella , Nuphar (Nymphaeaceae), Illicium , the monocots , and more derived angiosperms (eudicots), chloroplast genomes using cDNA and expressed sequence tags for floral genes, the cladogram shown below was generated. Acrogymnosperms Amborella Nuphar Illicium monocots magnoliids eudicots This hypothesized relationship of
2016-481: The carpel primordium ) produces the ovules , ovary septum, and the transmitting track, and plays a role in fusing the apical margins of carpels. The gynoecium may consist of one or more separate pistils. A pistil typically consists of an expanded basal portion called an ovary , an elongated section called a style and an apical structure called a stigma that receives pollen. The word "pistil" comes from Latin pistillum meaning pestle . A sterile pistil in
2072-468: The carpellate ("female") flowers have non-functional " staminodes ", structures resembling stamens in which no pollen develops. Plants may change from one reproductive morphology to the other. In one study, seven cuttings from a staminate plant produced, as expected, staminate flowers at their first flowering, but three of the seven produced carpellate flowers at their second flowering. The small, creamy white flowers are arranged in inflorescences borne in
2128-745: The common application of the term monotypic is frequently misleading, "since each taxon by definition contains exactly one type and is hence "monotypic", regardless of the total number of units", and suggests using "monospecific" for a genus with a single species, and "monotaxonomic" for a taxon containing only one unit. Species in monotypic genera tend to be more threatened with extinction than average species. Studies have found this pattern particularly pronounced in amphibians , where about 6.56% of monotypic genera are critically endangered , compared to birds and mammals where around 4.54% and 4.02% of monotypic genera face critical endangerment respectively. Studies have found that extinction of monotypic genera
2184-405: The constituent carpels may be referred to collectively as a single compound ovary. It can be a challenge to determine how many carpels fused to form a syncarpous gynoecium. If the styles and stigmas are distinct, they can usually be counted to determine the number of carpels. Within the compound ovary, the carpels may have distinct locules divided by walls called septa . If a syncarpous gynoecium has
2240-439: The developing seeds, and often aids in their dispersal. The gynoecium has several specialized tissues. The tissues of the gynoecium develop from genetic and hormonal interactions along three-major axes. These tissue arise from meristems that produce cells that differentiate into the different tissues that produce the parts of the gynoecium including the pistil, carpels, ovary, and ovules; the carpel margin meristem (arising from
2296-447: The disappearance of a genus, a family and an entire order, as well as the only witness to at least 140 million years of evolutionary history." Conservation strategies targeted on relict species are recommended, both preserving a diversity of habitats in New Caledonia and ex situ conservation in cultivation. Monotypic Monotypic taxa present several important theoretical challenges in biological classification . One key issue
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2352-566: The divergence of the Amborella lineage. One early 20th century idea of " primitive " (i.e. ancestral) floral traits in angiosperms, accepted until relatively recently, is the Magnolia blossom model. This envisions flowers with numerous parts arranged in spirals on an elongated, cone-like receptacle rather than the small numbers of parts in distinct whorls of more derived flowers. In a study designed to clarify relationships between well-studied model plants such as Arabidopsis thaliana , and
2408-476: The evolution of flowering plants. Some processes that have been considered congenital (phylogenetic) fusions appear to be non-fusion processes such as, for example, the de novo formation of intercalary growth in a ring zone at or below the base of primordia. Therefore, "it is now increasingly acknowledged that the term 'fusion,' as applied to phylogeny (as in 'congenital fusion') is ill-advised." Basal angiosperm groups tend to have carpels arranged spirally around
2464-486: The extant seed plants places Amborella as the sister taxon to all other angiosperms, and shows the gymnosperms as a monophyletic group sister to the angiosperms. It supports the theory that Amborella branched off from the main lineage of angiosperms before the ancestors of any other living angiosperms. There is however some uncertainty about the relationship between the Amborellaceae and the Nymphaeales : one theory
2520-417: The gynoecium produces megaspores , each of which develops into a female gametophyte which then produces egg cells. The term gynoecium is also used by botanists to refer to a cluster of archegonia and any associated modified leaves or stems present on a gametophyte shoot in mosses , liverworts , and hornworts . The corresponding terms for the male parts of those plants are clusters of antheridia within
2576-495: The hypanthium is present up to the base of the style(s), the flower is epigynous . In an epigynous flower, the stamens, petals, and sepals are attached to the hypanthium at the top of the ovary or, occasionally, the hypanthium may extend beyond the top of the ovary. Epigynous flowers are often referred to as having an inferior ovary . Plant families with epigynous flowers include orchids , asters , and evening primroses . Between these two extremes are perigynous flowers, in which
2632-427: The information content of biological classifications. As taxonomists Backlund and Bremer explain in their critique, "'Monotypic' taxa do not provide any information about the relationships of the immediately subordinate taxon". When monotypic taxa are sister to a single larger group, they might be merged into that group; however, when they are sister to multiple other groups, they may need to remain separate to maintain
2688-436: The lines of placentation can be regularly spaced along the wall of the ovary ( parietal placentation ), or near the center of the ovary. In the latter case, separate terms are used depending on whether or not the ovary is divided into separate locules. If the ovary is divided, with the ovules born on a line of placentation at the inner angle of each locule, this is axile placentation . An ovary with free central placentation , on
2744-457: The most basal lineage in the clade of angiosperms. In systematics the term "basal" describes a lineage that diverges near the base of a phylogeny, and thus earlier than other lineages. Since Amborella is apparently basal among the flowering plants, the features of early flowering plants can be inferred by comparing derived traits shared by the main angiosperm lineage but not present in Amborella . These traits are presumed to have evolved after
2800-402: The most challenging of the floral parts to interpret. Unlike (most) animals , plants grow new organs after embryogenesis , including new roots, leaves, and flowers. In the flowering plants, the gynoecium develops in the central region of the flower as a carpel or in groups of fused carpels. After fertilization, the gynoecium develops into a fruit that provides protection and nutrition for
2856-413: The most unobjectionable definition of the carpel is simply that of an appendage that encloses an ovule or ovules. If a gynoecium has a single carpel, it is called monocarpous . If a gynoecium has multiple, distinct (free, unfused) carpels, it is apocarpous . If a gynoecium has multiple carpels "fused" into a single structure, it is syncarpous . A syncarpous gynoecium can sometimes appear very much like
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#17327930430762912-438: The other extant species of flowering plants, and, among extant flowering plants, is the sister group to the other flowering plants. Comparing characteristics of this basal angiosperm, other flowering plants and fossils may provide clues about how flowers first appeared—what Darwin called the "abominable mystery". This position is consistent with a number of conservative characteristics of its physiology and morphology; for example,
2968-438: The other hand, consists of a single compartment without septae and the ovules are attached to a central column that arises directly from the floral apex (axis). In some cases a single ovule is attached to the bottom or top of the locule ( basal or apical placentation , respectively). In flowering plants, the ovule (from Latin ovulum meaning small egg) is a complex structure born inside ovaries. The ovule initially consists of
3024-409: The ovules. This structure is typically rolled and fused along the margin. Although many flowers satisfy the above definition of a carpel, there are also flowers that do not have carpels because in these flowers the ovule(s), although enclosed, are borne directly on the floral apex. Therefore, the carpel has been redefined as an appendage that encloses ovule(s) and may or may not bear them. However,
3080-407: The wall of the inferior ovary results from the "congenital" fusion of dorsal carpel flanks and the floral axis does not correspond to the ontogenetic processes that can actually be observed. All that can be seen is an intercalary growth in a broad circular zone that changes the shape of the floral axis (receptacle)." And what happened during evolution is not a phylogenetic fusion but the formation of
3136-577: The wood of Amborella lacks the vessels characteristic of most flowering plants. The genes responsible for floral traits like scent and colors in other angiosperms, have yet to be found. Further, the female gametophyte of Amborella is even more reduced than normal female angiosperm gametophyte . Amborella , being an understory plant in the wild, is commonly in intimate contact with shade- and moisture-dependent organisms such as algae, lichens and mosses. In those circumstances, some horizontal gene transfer between Amborella and such associated species
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