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Peridiscaceae is a
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
of
flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. They include all forbs (flowering plants without a woody stem), grasses and grass-like plants, a vast majority of ...
s in the
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Saxifragales.Peter F. Stevens. 2001 onwards. "Peridiscaceae". At: Angiosperm Phylogeny Website At: Missouri Botanical Garden Website. (see ''External links'' below). Four
genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...
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,
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 forest ...
'', and ''
Whittonia ''Whittonia'' is a monotypic genus of flowering plants belonging to the family Peridiscaceae. It only contains one known species, 'Whittonia guianensis'Sandwith It is native to Guyana. The genus name of ''Whittonia'' is in honour of Brian Alan ...
''.,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 ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in ...
and northern
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
, ''Whittonia'' in Guyana,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 (; french: Cameroun, ff, Kamerun), officially the Republic of Cameroon (french: République du Cameroun, links=no), is a country in west- central Africa. It is bordered by Nigeria to the west and north; Chad to the northeast; th ...
, and ''Soyauxia'' in
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
West Africa West Africa or Western Africa is the westernmost region of Africa. The United Nations defines Western Africa as the 16 countries of Benin, Burkina Faso, Cape Verde, The Gambia, Ghana, Guinea, Guinea-Bissau, Ivory Coast, Liberia, Mali, Mau ...
.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, 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 ...
collected below Kaieteur Falls 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, including only woody plants with secondary growth, plants that are ...
s or erect shrubs of wet tropical
forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...
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, including only woody plants with secondary growth, plants that are ...
s or erect shrubs. The leaves are stipulate, alternate, and simple, with margins that are entire or remotely crenulate (''Medusandra''). The petiole is pulvinate, at its apex, sometimes obscurely so. The stipules are in the
axil A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ...
s of the leaves, sometimes enclosing an axillary bud. The
inflorescence An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed ...
is a cluster of axillary
raceme A raceme ( or ) or racemoid is an unbranched, 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 produced as the sh ...
s or spikes, the clusters often being reduced to a pair of racemes or to a single raceme. The
flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...
s are bisexual and actinomorphic. 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 The term ''sepalum'' was coined ...
s are 4 to 7 in number, and
free Free may refer to: Concept * Freedom, having the ability to do something, without having to obey anyone/anything * Freethought, a position that beliefs should be formed only on the basis of logic, reason, and empiricism * Emancipate, to procur ...
, that is, separate from each other. ''Medusandra'' and ''Soyauxia'' have five
petal Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corolla''. Petals are usuall ...
s. ''Peridiscus'' and ''Whittonia'' have none. ''Medusandra'' lacks a nectary disk and has five
stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filam ...
s, inserted opposite the petals, and alternating with five long, hairy staminodes. In the others, the stamens are numerous and arranged in a ring around the nectary disk. The anthers are tetra thecal in ''Medusandra'' and ''Soyauxia''; bithecal in ''Peridiscus'' and ''Whittonia''. The perianth parts are attached below the
ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the bod ...
. 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 *Lake ...
, but appears half-inferior in ''Peridiscus'' because the ovary is embedded in the large, fleshy disk. The
gynoecium Gynoecium (; ) 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) '' pistil ...
consists of three or four
carpel Gynoecium (; ) 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) '' pistils' ...
s, united to form a unilocular ovary. The
placentation Placentation refers to the formation, type and structure, or 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 remov ...
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 megasporangium), and the f ...
s at the apex of each carpel. The ovary has a central column in ''Medusandra'' and ''Soyauxia''. Each carpel bears a
stylulus ''Stylulus'' is a genus of ground beetles in the family Carabidae Ground beetles are a large, cosmopolitan family of beetles, the Carabidae, with more than 40,000 species worldwide, around 2,000 of which are found in North America and 2,700 in ...
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 that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in partic ...
is one-
seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiosper ...
ed; a capsule in ''Medusandra'' and ''Soyauxia''; a
drupe In botany, a drupe (or stone fruit) is an indehiscent fruit in which an outer fleshy part ( exocarp, or skin, and mesocarp, or flesh) surrounds a single shell (the ''pit'', ''stone'', or '' pyrena'') of hardened endocarp with a seed (''kerne ...
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 studi ...
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 () The New Oxford Dictionary of English (1998) – p. 633 "Etymology /ˌɛtɪˈmɒlədʒi/ the study of the class in words and the way their meanings have changed throughout time". is the study of the history of the form of words ...
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 ''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 ...
'', placing it in the family Passifloraceae.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 botanist and plant collector
Hermann Soyaux Hermann Soyaux (4 January 1852, Breslau – 1928, Brazil) was a German botanist and explorer. Biography Soyaux was initially a horticulturalist and then studied botany in Berlin. The ''Deutsche Afrika Gesellschaft'' (German Africa Society) fund ...
,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 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 John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Seco ...
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 for the ''rbcL''
gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
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.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, Pamela S. Soltis, Peter Weston, W. Mark Whitten, Kenneth J. Wurdack and Mark W. Chase. 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 with Elatinaceae 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 Worl ...
, a very surprising and unexpected result. On the basis of this
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...
, the Angiosperm Phylogeny Group placed Peridiscaceae in
Malpighiales The Malpighiales comprise one of the largest orders of flowering plants, containing about 36 families and more than species, about 7.8% of the eudicots. The order is very diverse, containing plants as different as the willow, violet, poinse ...
when they published the APG II system of
plant classification The history of plant systematics—the biological classification of plants—stretches from the work of ancient Greek to modern evolutionary biologists. As a field of science, plant systematics came into being only slowly, early plant lo ...
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, formed by DNA from unidentified plants that had contaminated the 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 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 known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it ...
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 us ...
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. 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), a social group {{disambig ...
, finding strong support for a clade of 'Medusandra'' + (''Soyauxia'' + ''Peridiscus'') When the APG III system 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 (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...
is diagrammed as a phylogenetic tree 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
taxa In biology, a taxon ( back-formation from '' taxonomy''; plural 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 n ...
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. * {{Taxonbar, from=Q132930 Saxifragales families