Peridiscaceae
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Peridiscaceae is a
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
of
flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
s in the
order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...
Saxifragales Saxifragales is an order (biology), order of flowering plants in the Superrosids, superrosid clade of the eudicots. It contains 15 Families (biology), families and around 100 genera, with nearly 2,500 species. Well-known and economically import ...
.Peter F. Stevens. 2001 onwards. "Peridiscaceae". At: Angiosperm Phylogeny Website At: Missouri Botanical Garden Website. (see ''External links'' below). Four
genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
comprise this family: ''
Medusandra ''Medusandra'' is a genus of flowering plants in the family Peridiscaceae."Peridiscaceae" At: Peter F. Stevens (2001 onwards). Angiosperm Phylogeny Website. At: Missouri Botanical Garden Website. (see external links below) It has two species, '' ...
,
Soyauxia ''Soyauxia'' is a genus of flowering plants in the family Peridiscaceae.Clemens Bayer. 2007. "Peridiscaceae" pages 297-300. In: Klaus Kubitski (editor). ''The Families and Genera of Vascular Plants'' volume IX. Springer-Verlag: Berlin;Heidelber ...
,
Peridiscus ''Peridiscus lucidus'' is a species of flowering plant, the only species in the genus ''Peridiscus'', which is one of four genera within the family Peridiscaceae. It grows in Venezuela and northern Brazil, in evergreen, sometimes riverine fores ...
'', and ''
Whittonia ''Whittonia'' is a monotypic genus of flowering plants belonging to the family Peridiscaceae. It only contains one known species, ''Whittonia guianensis''. It is native to Guyana. The genus name of ''Whittonia'' is in honour of Brian Alan Wh ...
''.,Kenneth J. Wurdack and Charles C. Davis. 2009. "Malpighiales phylogenetics: Gaining ground on one of the most recalcitrant clades in the angiosperm tree of life." ''American Journal of Botany'' 96(8):1551-1570. with a total of 12 known species. It has a
disjunct distribution In biology, a taxon with a disjunct distribution is one that has two or more groups that are related but considerably separated from each other geographically. The causes are varied and might demonstrate either the expansion or contraction of a s ...
, with ''Peridiscus'' occurring in
Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...
and northern
Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
, ''Whittonia'' in
Guyana Guyana, officially the Co-operative Republic of Guyana, is a country on the northern coast of South America, part of the historic British West Indies. entry "Guyana" Georgetown, Guyana, Georgetown is the capital of Guyana and is also the co ...
,Clemens Bayer. 2007. "Peridiscaceae" pages 297-300. In: Klaus Kubitski (editor). ''The Families and Genera of Vascular Plants'' volume IX. Springer-Verlag: Berlin;Heidelberg, Germany. ''Medusandra'' in
Cameroon Cameroon, officially the Republic of Cameroon, is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the R ...
, and ''Soyauxia'' in
tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...
West Africa West Africa, also known as Western Africa, is the westernmost region of Africa. The United Nations geoscheme for Africa#Western Africa, United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Gha ...
.Vernon H. Heywood, Richard K. Brummitt, Ole Seberg, and Alastair Culham. ''Flowering Plant Families of the World''. Firefly Books: Ontario, Canada. (2007). ''Whittonia'' is possibly
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
, being known from only one
specimen Specimen may refer to: Science and technology * Sample (material), a limited quantity of something which is intended to be similar to and represent a larger amount * Biological specimen or biospecimen, an organic specimen held by a biorepository f ...
collected below
Kaieteur Falls Kaieteur Falls is one of the most powerful single-drop waterfalls in the world. It is located on the Potaro River in Kaieteur National Park, central Essequibo Territory, Guyana. It is 226 metres (741 ft) high when measured from its plunge ...
in Guyana. In 2006, archeologists attempted to rediscover it, however, it proved unsuccessful. The largest genus is ''Soyauxia'', with about seven species. ''Medusandra'' has two species. ''Peridiscus'' and ''Whittonia'' each contain one species. The Peridiscaceae are small
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...
s or erect
shrub A shrub or bush is a small to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple ...
s of wet tropical
forest A forest is an ecosystem characterized by a dense ecological community, community of trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, ...
s. It was not until 2009 that all four of the genera were united into a single family. ''Peridiscus'' and ''Whittonia'' are clearly close relatives. This pair, and the other two genera have long been considered anomalous, being variously classified by different authors.


Description

The following description was created by combining descriptions of ''Medusandra'' and ''Peridiscus'' by John HutchinsonJohn Hutchinson. ''The Families of Flowering Plants, Third Edition (1973)''. Oxford University Press: London. with descriptions of ''Soyauxia'', ''Peridiscus'', and ''Whittonia'' by Clemens Bayer. Peridiscaceae are small
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...
s or erect
shrub A shrub or bush is a small to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple ...
s. The leaves are stipulate,
alternate Alternative or alternate may refer to: Arts, entertainment and media * Alternative (''Kamen Rider''), a character in the Japanese TV series ''Kamen Rider Ryuki'' * Alternative comics, or independent comics are an alternative to mainstream superh ...
, and
simple Simple or SIMPLE may refer to: *Simplicity, the state or quality of being simple Arts and entertainment * ''Simple'' (album), by Andy Yorke, 2008, and its title track * "Simple" (Florida Georgia Line song), 2018 * "Simple", a song by John ...
, with margins that are
entire Entire may refer to: * Entire function, a function that is holomorphic on the whole complex plane * Entire (animal), an indication that an animal is not neutered * Entire (botany) This glossary of botanical terms is a list of definitions o ...
or remotely
crenulate The following terms are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (that is, the leaf blade or 'lamina' is undivided) or compound (that is, the leaf blade is divided into two or more leaflets) ...
(''Medusandra''). The
petiole Petiole may refer to: *Petiole (botany), the stalk of a leaf, attaching the blade to the stem *Petiole (insect anatomy) In entomology, petiole is the technical term for the narrow waist of some hymenopteran insects, especially ants, bees, and ...
is pulvinate, at its
apex The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics) A-Bomb Abomination Absorbing Man Abraxas Abyss Abyss is the name of two characters appearing in Ameri ...
, sometimes obscurely so. The stipules are in the
axil A leaf (: leaves) 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, fl ...
s of the leaves, sometimes enclosing an axillary
bud In botany, a bud is an undeveloped or Plant embryogenesis, embryonic Shoot (botany), shoot and normally occurs in the axil of a leaf or at the tip of a Plant stem, stem. Once formed, a bud may remain for some time in a dormancy, dormant conditi ...
. The
inflorescence In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...
is a cluster of axillary
raceme A raceme () or racemoid is an unbranched, indeterminate growth, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are ...
s or
spike Spike, spikes, or spiking may refer to: Arts, entertainment, and media Books * ''The Spike'' (novel), a novel by Arnaud de Borchgrave * ''The Spike'' (Broderick book), a nonfiction book by Damien Broderick * ''The Spike'', a starship in Peter ...
s, the clusters often being reduced to a pair of racemes or to a single raceme. The
flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...
s are bisexual and
actinomorphic Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spirall ...
. The
sepal A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 Etymology The term ''sepalum'' ...
s are 4 to 7 in number, and
free Free may refer to: Concept * Freedom, the ability to act or change without constraint or restriction * Emancipate, attaining civil and political rights or equality * Free (''gratis''), free of charge * Gratis versus libre, the difference betw ...
, that is, separate from each other. ''Medusandra'' and ''Soyauxia'' have five
petal Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...
s. ''Peridiscus'' and ''Whittonia'' have none. ''Medusandra'' lacks a
nectar Nectar is a viscous, sugar-rich liquid produced by Plant, plants in glands called nectaries, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to an ...
y disk and has five
stamen The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...
s, inserted opposite the petals, and alternating with five long, hairy
staminode In botany, a staminode is an often rudimentary, sterile or abortive stamen, which means that it does not produce pollen.Jackson, Benjamin, Daydon; ''A Glossary of Botanic Terms with their Derivation and Accent''; Published by Gerald Duckworth & Co ...
s. In the others, the stamens are numerous and arranged in a ring around the nectary disk. The
anther The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...
s are tetra
theca In biology, a theca (: thecae) is a sheath or a covering. Botany In botany, the theca is related to plant's flower anatomy. The theca of an angiosperm consists of a pair of microsporangia that are adjacent to each other and share a common ar ...
l in ''Medusandra'' and ''Soyauxia''; bithecal in ''Peridiscus'' and ''Whittonia''. The
perianth The perianth (perigonium, perigon or perigone in monocots) is the non-reproductive part of the flower. It is a structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals) or tepal ...
parts are attached below the
ovary The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/ oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are end ...
. The ovary is therefore
superior Superior may refer to: *Superior (hierarchy), something which is higher in a hierarchical structure of any kind Places * Superior (proposed U.S. state), an unsuccessful proposal for the Upper Peninsula of Michigan to form a separate state *Lak ...
, but appears half-inferior in ''Peridiscus'' because the ovary is embedded in the large, fleshy disk. The
gynoecium Gynoecium (; ; : gynoecia) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl (botany), whorl of a flower; it consists ...
consists of three or four
carpel Gynoecium (; ; : gynoecia) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more ...
s, united to form a unilocular ovary. The
placentation Placentation is the formation, type and structure, or modes of arrangement of the placenta. The function of placentation is to transfer nutrients, respiratory gases, and water from maternal tissue to a growing embryo, and in some instances to re ...
is apical, with two
ovule In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the sporangium, megasporangium), ...
s at the apex of each carpel. The ovary has a central column in ''Medusandra'' and ''Soyauxia''. Each carpel bears a stylulus and these are well separated at the apex of the ovary. The
fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...
is one-
seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...
ed; a capsule in ''Medusandra'' and ''Soyauxia''; a
drupe In botany, a drupe (or stone fruit) is a type of fruit in which an outer fleshy part (exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pip'' (UK), ''pit'' (US), ''stone'', or ''pyrena'') of hardened endocarp with a seed ...
in ''Peridiscus'' and ''Whittonia''.


History

George Bentham George Bentham (22 September 1800 – 10 September 1884) was an English botanist, described by the weed botanist Duane Isely as "the premier systematic botanist of the nineteenth century". Born into a distinguished family, he initially studie ...
established the genus ''Peridiscus'' in 1862, naming its only species ''Peridiscus lucidus''. He placed it in a group which he called "Tribus Flacourtieae" and which later would be known as the family
Flacourtiaceae The Flacourtiaceae is a defunct family of flowering plants whose former members have been scattered to various families, mostly to the Achariaceae and Salicaceae. It was so vaguely defined that hardly anything seemed out of place there and it bec ...
.George Bentham and Joseph Dalton Hooker. 1862. ''Genera Plantarum'' volume 1, part 1, page 127. A. Black, William Pamplin, Lovell Reeve & Co., Williams & Norgate: London, England. (see ''External links'' below). Bentham wrote no
etymology Etymology ( ) is the study of the origin and evolution of words—including their constituent units of sound and meaning—across time. In the 21st century a subfield within linguistics, etymology has become a more rigorously scientific study. ...
for this name, but it is generally believed that the name refers to the fact that the stamens are attached along the outer edge of the nectary disk.Umberto Quattrocchi. 2000. ''CRC World Dictionary of Plant Names''. volume III, page 2010. CRC Press: Baton Rouge, New York, London, Washington DC. . (see ''External links'' below) Daniel Oliver established the genus ''Soyauxia'' in 1880 for '' Soyauxia gabonensis'', placing it in the family
Passifloraceae The Passifloraceae are a family of flowering plants, containing about 750 species classified in around 27 genera. They include trees, shrubs, lianas, and climbing plants, and are mostly found in tropical regions. The family takes its name from t ...
.Joseph Dalton Hooker. 1880. ''Hooker's Icones Plantarum'' volume XIV (volume IV of the third series):page 73 and plate 1393. (see ''External links'' below). He named it for the
German German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ge ...
botanist and plant collector Hermann Soyaux,Umberto Quattrocchi. 2000. ''CRC World Dictionary of Plant Names''. volume IV, page 2521. CRC Press: Baton Rouge, New York, London, Washington DC. . saying "Mons. Soyaux, now settled in the Gaboon, well deserves that his name should be associated with one of his interesting discoveries in that region". The family Flacourtiaceae was, as Hermann Sleumer said, a fiction,Regis B. Miller (1975). "Systematic anatomy of the xylem and comments on the relationships of Flacourtiaceae". ''Journal of the Arnold Arboretum'' 56(1):79.Mark W. Chase, Sue Zmarzty, M. Dolores Lledó, Kenneth J. Wurdack, Susan M. Swensen, and Michael F. Fay. 2002. "When in doubt, put it in Flacourtiaceae: a molecular phylogenetic analysis based on plastid ''rbcL'' DNA sequences." ''Kew Bulletin'' 57(1):141-181. and ''Peridiscus'' was, from the outset, one of its most doubtful members. Recognizing its distinctiveness, João Kuhlmann segregated it into its own family in 1947.João G. Kuhlmann. 1947. "Peridiscaceae (Kuhlmann)". ''Arquivos do Serviço Florestal'' 3(1):3-7. In 1952, John Brenan named and described ''Medusandra'', erecting a new family,
Medusandraceae ''Medusandra'' is a genus of flowering plants in the family Peridiscaceae."Peridiscaceae" At: Peter F. Stevens (2001 onwards). Angiosperm Phylogeny Website. At: Missouri Botanical Garden Website. (see external links below) It has two species, '' ...
to accommodate it.John P.M. Brenan. 1952. "Plants of the Cambridge Expedition, 1947-1948: II. A new order of flowering plants from the British Cameroons". ''Kew Bulletin'' 7:227-236. In 1953, Brenan transferred ''Soyauxia'' from Passifloraceae to Medusandraceae,John P.M. Brenan. 1953. "''Soyauxia'', a second genus of Medusandraceae". ''Kew Bulletin'' 8:507-511. but few others agreed with his classification. In 1954, John Hutchinson and John McEwen Dalziel followed Brenan's treatment in the second edition of their ''Flora of West Tropical Africa''. Hutchinson, however, soon recanted, explaining in some detail why he thought that ''Medusandra'' and ''Soyauxia'' were not related. In 1962, Noel Y. Sandwith named and described ''Whittonia''.Noel Y. Sandwith. 1962. "Contributions to the flora of tropical America: LXIX. A new genus of Peridiscaceae". ''Kew Bulletin'' 15:467-471. In an accompanying article, Charles Russell Metcalfe discussed its close relationship to ''Peridiscus''. For four decades thereafter, Peridiscaceae was viewed as a family of uncertain taxonomic position, containing two genera. In the year 2000, a
DNA sequence A nucleic acid sequence is a succession of bases within the nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. This succession is denoted by a series of a set of five different letters that indicate the order of the nu ...
for the ''rbcL''
gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
of ''Whittonia'' was produced and used in a
molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
study of the
eudicots The eudicots or eudicotyledons are flowering plants that have two seed leaves (cotyledons) upon germination. The term derives from ''dicotyledon'' (etymologically, ''eu'' = true; ''di'' = two; ''cotyledon'' = seed leaf). Historically, authors h ...
.Vincent Savolainen, Michael F. Fay, Dirk C. Albach, Anders Backlund, Michelle van der Bank, Kenneth M. Cameron, S.A. Johnson, M. Dolores Lledo, Jean-Christophe Pintaud, Martyn P. Powell, Mary Clare Sheahan,
Douglas E. Soltis Douglas Soltis is a Distinguished Professor in the Laboratory of Molecular Systematics & Evolutionary Genetics (Soltis lab), Florida Museum of Natural History, and Department of Biology at the University of Florida. His research interests are i ...
, Pamela S. Soltis, Peter Weston, W. Mark Whitten, Kenneth J. Wurdack and
Mark W. Chase Mark Wayne Chase (born 1951) is a US-born British botanist. He is noted for work in plant classification and evolution, and one of the instigators of the Angiosperm Phylogeny Group-classification for flowering plants which is partly based on DNA ...
. 2000. "Phylogeny of the eudicots: a nearly complete familial analysis based on ''rbcL'' gene sequences". ''Kew Bulletin'' 55(2):257-309.
This study placed Peridiscaceae in a
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
with
Elatinaceae Elatinaceae is a family of flowering plants with ca 35 (to perhaps 50) species in two genera: ''Elatine'' and ''Bergia''. The ''Elatine'' are mostly aquatic herbs, and the ''Bergia'' are subshrubs to shrubs. ''Elatine'' species are widely distri ...
and
Malpighiaceae Malpighiaceae is a family of flowering plants in the order Malpighiales. It comprises about 73 genera and 1315 species, all of which are native to the tropics and subtropics. About 80% of the genera and 90% of the species occur in the New World ( ...
, a very surprising and unexpected result. On the basis of this
phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...
, the
Angiosperm Phylogeny Group The Angiosperm Phylogeny Group (APG) is an informal international group of systematic botanists who collaborate to establish a consensus on the taxonomy of flowering plants (angiosperms) that reflects new knowledge about plant relationships disc ...
placed Peridiscaceae in
Malpighiales The Malpighiales comprise one of the largest Order (biology), orders of flowering plants. The order is very diverse, with well-known members including willows, Viola (plant), violets, aspens and Populus, poplars, Euphorbia pulcherrima, poinsett ...
when they published the
APG II system The APG II system (Angiosperm Phylogeny Group II system) of plant classification is the second, now obsolete, version of a modern, mostly Molecular phylogenetics, molecular-based, list of systems of plant taxonomy, system of plant taxonomy that ...
of plant classification in 2003.The Angiosperm Phylogeny Group. 2003. "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II". ''Botanical Journal of the Linnean Society'' 141(4):399-436. It was soon found that the ''rbcL'' sequence for ''Whittonia'' was a
chimera Chimera, Chimaera, or Chimaira (Greek for " she-goat") originally referred to: * Chimera (mythology), a fire-breathing monster of ancient Lycia said to combine parts from multiple animals * Mount Chimaera, a fire-spewing region of Lycia or Cilicia ...
, formed by
DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...
from unidentified plants that had contaminated the
sample Sample or samples may refer to: * Sample (graphics), an intersection of a color channel and a pixel * Sample (material), a specimen or small quantity of something * Sample (signal), a digital discrete sample of a continuous analog signal * Sample ...
. No subsequent attempt to extract DNA from ''Whittonia'' has been made. In 2004, using DNA from ''Peridiscus'', it was shown that Elatinaceae and Malpighiaceae are indeed
sister A sister is a woman or a girl who shares parents or a parent with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a familial relationship, it is sometimes used endearingly to ref ...
families and that Peridiscaceae belong to Saxifragales. ''Medusandra'' and ''Soyauxia'', meanwhile, were listed in APG II in an appendix entitled "TAXA OF UNCERTAIN POSITION". DNA from ''Soyauxia'' was eventually obtained, and in 2007, it was shown that ''Soyauxia'' is most closely related to ''Peridiscus'' and, presumably, ''Whittonia''. Since this result has a good morphological basis, ''Soyauxia'' was duly transferred to Peridiscaceae. This study also found strong statistical support for the inclusion of Peridiscaceae in Saxifragales, but no strong support for any particular position within that order. In 2008, in a study employing a large amount of
chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...
DNA data, as well as some
mitochondrial A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...
and
nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: *Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics * Nuclear space *Nuclear ...
DNA, it was shown that Peridiscaceae is sister to the rest of Saxifragales.Shuguang Jian, Pamela S. Soltis, Matthew A. Gitzendanner, Michael J. Moore, Ruiqi Li, Tory A. Hendry, Yin-Long Qiu, Amit Dhingra, Charles D. Bell, and
Douglas E. Soltis Douglas Soltis is a Distinguished Professor in the Laboratory of Molecular Systematics & Evolutionary Genetics (Soltis lab), Florida Museum of Natural History, and Department of Biology at the University of Florida. His research interests are i ...
. 2008. "Resolving an Ancient, Rapid Radiation in Saxifragales". ''Systematic Biology'' 57(1):38-57.
It had been suspected that ''Medusandra'' might belong somewhere in Malpighiales, but a phylogeny of that order, generated in 2009, placed ''Medusandra'' in Saxifragales. The authors had included ''Medusandra'' and a few other members of Saxifragales in their
outgroup Outgroup may refer to: * Outgroup (cladistics), an evolutionary-history concept * Outgroup (sociology) In social psychology and sociology, an in-group is a social group to which a person psychologically identifies as being a member. By cont ...
, finding strong support for a clade of 'Medusandra'' + (''Soyauxia'' + ''Peridiscus'') When the
APG III system The APG III system of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy being developed by the Angiosperm Phylogeny Group (APG). Published in 2009, it was superseded in 2016 by a f ...
was published in October 2009, Peridiscaceae was expanded to include ''Medusandra'' and ''Soyauxia''. John Brenan, 57 years before, had been prescient in his perception of a relationship between ''Medusandra'' and ''Soyauxia''.


Phylogeny

The
phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...
is diagrammed as a
phylogenetic tree A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA. In ...
below. The relationships shown are from Wurdack and Davis (2009) except for the position of ''Whittonia'', for which no DNA sequences are known. ''Peridiscus'' and ''Whittonia'' are undoubtedly
sister A sister is a woman or a girl who shares parents or a parent with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a familial relationship, it is sometimes used endearingly to ref ...
taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
due to their many shared morphological characters.


References


Bibliography

* * * * * * ;Websites
Peridiscaceae
At

At
Missoure Botanical Garden Website

CRC World Dictionary of Plant Names: M-Q
At
Hooker's Icones Plantarum


in L. Watson and M.J. Dallwitz (1992 onwards)
The families of flowering plants
descriptions, illustrations, identification, information retrieval. * {{Authority control Saxifragales families