An atoll, sometimes called a coral atoll, is a ring-shaped coral reef including a coral rim that encircles a lagoon or completely. There may be coral cays on the rim; the coral of the atoll sits atop the rim of an extinct seamount or volcano which has eroded or subsided beneath the water. The lagoon forms over the volcanic crater or caldera while the higher rim remains above water or at shallow depths that permit the coral to grow and form the reefs. For the atoll to persist, continued erosion or subsidence must be at a rate slow enough to permit reef growth upward and outward to replace the lost height; the word atoll comes from the Dhivehi word atholhu. OED Its first recorded use in English was in 1625 as atollon. Charles Darwin recognized its indigenous origin and coined, in his The Structure and Distribution of Coral Reefs, the definition of atolls as "circular groups of coral islets", synonymous with "lagoon-island". More modern definitions of atoll describe them as "annular reefs enclosing a lagoon in which there are no promontories other than reefs and islets composed of reef detritus" or "in an morphological sense, a ring-shaped ribbon reef enclosing a lagoon".

There are 440 atolls. Most of the world's atolls are in the Indian Ocean; the Atlantic Ocean has no large groups of atolls, other than eight atolls east of Nicaragua that belong to the Colombian department of San Andres and Providencia in the Caribbean. Reef-building corals will thrive only in warm tropical and subtropical waters of oceans and seas, therefore atolls are only found in the tropics and subtropics; the northernmost atoll of the world is Kure Atoll at 28°24′ N, along with other atolls of the Northwestern Hawaiian Islands. The southernmost atolls of the world are Elizabeth Reef at 29°58′ S, nearby Middleton Reef at 29°29′ S, in the Tasman Sea, both of which are part of the Coral Sea Islands Territory; the next southerly atoll is Ducie Island in the Pitcairn Islands Group, at 24°40′ S. Bermuda is sometimes claimed as the "northernmost atoll" at a latitude of 32°24′ N. At this latitude coral reefs would not develop without the warming waters of the Gulf Stream. However, Bermuda is termed a pseudo-atoll because its general form, while resembling that of an atoll, has a different mode of formation.

While there is no atoll directly on the Equator, the closest atoll to the Equator is Aranuka of Kiribati, with its southern tip just 12 km north of the Equator. In most cases, the land area of an atoll is small in comparison to the total area. Atoll islands are low lying, with their elevations less than 5 meters. Measured by total area, Lifou is the largest raised coral atoll of the world, followed by Rennell Island. More sources however list as the largest atoll in the world in terms of land area Kiritimati, a raised coral atoll, 160 km2 main lagoon, 168 km2 other lagoons; the remains of an ancient atoll as a hill in a limestone area is called a reef knoll. The second largest atoll by dry land area is Aldabra with 155 km2; the largest atoll in terms of island numbers is Huvadhu Atoll in the south of the Maldives with 255 islands. In 1842, Charles Darwin explained the creation of coral atolls in the southern Pacific Ocean based upon observations made during a five-year voyage aboard HMS Beagle from 1831 to 1836.

Accepted as correct, his explanation involved considering that several tropical island types—from high volcanic island, through barrier reef island, to atoll—represented a sequence of gradual subsidence of what started as an oceanic volcano. He reasoned that a fringing coral reef surrounding a volcanic island in the tropical sea will grow upward as the island subsides, becoming an "almost atoll", or barrier reef island, as typified by an island such as Aitutaki in the Cook Islands, Bora Bora and others in the Society Islands; the fringing reef becomes a barrier reef for the reason that the outer part of the reef maintains itself near sea level through biotic growth, while the inner part of the reef falls behind, becoming a lagoon because conditions are less favorable for the coral and calcareous algae responsible for most reef growth. In time, subsidence carries the old volcano below the ocean surface and the barrier reef remains. At this point, the island has become an atoll. Atolls are the product of the growth of tropical marine organisms, so these islands are only found in warm tropical waters.

Volcanic islands located beyond the warm water temperature requirements of hermatypic organisms become seamounts as they subside and are eroded away at the surface. An island, located where the ocean water temperatures are just sufficiently warm for upward reef growth to keep pace with the rate of subsidence is said to be at the Darwin Point. Islands in colder, more polar regions evolve toward guyots. Reginald Aldworth Daly offered a somewhat different explanation for atoll formation: islands worn away by erosion, by ocean waves and streams, during the last glacial stand of the sea of some 900 feet below present sea level developed as coral islands, or barrier reefs on a platform surrounding a volcanic island no

Canna paniculata

Canna paniculata Ruiz & Pav. is a species of the Canna genus, belonging to the family Cannaceae. Native of southern Mexico, Costa Rica, tropical South America, except for the Amazon Basin, at 200-2,000m, it is a perennial growing to 5 m tall. It is frost tender. In the north latitudes it is in flower from August to October, the seeds ripen in October; the flowers are hermaphrodite. In addition to the above agreed synonyms, there is a major reference to Canna'Musaefolia', admitting that it was earlier called C. excelsa Lodd. but renamed in France by Monsieur Theodoré Anneé because of its resemblance to Musa. In the last three decades of the 20th century, Canna species have been categorised by two different taxonomists, Paulus Johannes Maria Maas from the Netherlands and Nobuyuki Tanaka from Japan, they are in agreement that this is a distinct and separate species. Canna paniculata grows to 5 m tall. Leaves green, sessile or shortly but distinctly petiolate, petiole with pulvinus, lower side, lower side of leaves lanuginose.

Inflorescence branched. Flowers erect, red to yellow or scarlet, 6–10 cm long, composed of 6 coloured parts of about equal length. Chaté, E.. Le Canna, son histoire, son culture. Libraire Centrale d'Agriculture et de Jardinage. Cooke, Ian, 2001; the Gardener's Guide to Growing cannas, Timber Press. ISBN 0-88192-513-6 Johnson's Gardeners Dictionary, 1856 Tanaka, N. 2001. Taxonomic revision of the family Cannaceae in Asia. Makinoa ser. 2, 1:34–43. Kew Gardens, Checklist of plant families

Rugby union in Kenya

Rugby union in Kenya is a popular sport, in particular due to the success of the Kenya national rugby sevens team in the rugby sevens format, tournaments such as the Safari Sevens, growing yearly, now includes numerous international teams. The sport is governed by the Kenya Rugby Union; the Rugby Football Union of Kenya was formed in 1923. RFU-K was incorporated into the Rugby Football Union of East Africa in 1956. Kenya Rugby Football Union was formed in 1970 to govern the game in Kenya. At the 2008 Kenyan Sports Personality of the Year awards KRFU won the federation of the year category. Rugby has a long history in Kenya; the first recorded game in Kenya took place in 1909, when a team composed of predominantly British "Officials" took on Afrikaaner "Settlers" in Mombasa. The Rugby Football Union of Kenya was formed in 1923, the same year when Nairobi District team split to form Harlequins RFC and Nondescripts RFC. Impala RFC, another traditional club was founded in the 1930s. For a number of years, the Nondescripts and the Harlequins were two of the best sides in the country and dominated Kenyan rugby.

When the British Isles went to South Africa for their 1955 tour and their 1962 tour, they played East Africa sides in Nairobi, on the return leg of their journey. The Lions won both of 39-12 and 50-0 respectively; the East Africa team played some of the best sides in the world, including the British Lions in 1955, South Africa in 1961, Wales in 1964. The political struggle in Kenya took a heavy toll on rugby. Not only had the white population failed to promote the game properly amongst the black African and Asian population in Kenya, but when employment restrictions were introduced by the newly independent Kenyan state, they ensured that a number of the white British and South Africans, the mainstay of the game left the country; the large distances involved would cause big communication problems for Kenyan teams. For example, in 1974, when Nairobi was due to play Mombasa, the Mombasa team flew to Nairobi, while the Nairobi team drove to Mombasa, it was a 950-mile round trip, meaning that the two teams covered nearly 2,000 miles in a game that didn't happen.

Until the mid-1970s the sport in Kenya was played by expatriates. This changed once Mean Machine RFC and Mwamba RFC were formed. Today, rugby in Kenya is played exclusively by indigenous players. Rugby in Kenya is played in Nairobi, only a handful of teams come from outside the capital; the struggle to make Kenyan rugby multiracial, to make it popular was tackled frantically by the KRFU in the post-independence period, with success only coming under its president George Kariuki in the 1980s and 1990s. The former Gloucester player Dave Protherough helped out the KRFU, before his death in the mid-1990s, helped the game to thrive once more. Kenya is a founder member of the Confederation of African Rugby, launched in January 1986, in Tunis. Rugby officials from Morocco, Ivory Coast, the Seychelles and Madagascar attended. Kenya plays host to the annual Bamburi Rugby Super Series which teams from other East African countries attend. In 2009, it hosted the IRB Junior World Rugby Trophy, the second tier of the under-20 world championship structure established in 2008 by the sport's governing body, the International Rugby Board.

Safari Sevens is an international Rugby sevens tournament played annually in Nairobi and is the most popular rugby competition in Kenya. Kenya dominated the local'international' rugby scene but when combined with Tanzania and Uganda they formed the East Africa rugby union team; this consisted of white settlers from Kenya, the games tended to be hosted in Nairobi. Nicknamed The Tuskers, a name, taken from a local beer, the first overseas touring East Africa XV played in the Copperbelt of what was Northern Rhodesia, now Zambia, in September 1954 when they won six out of seven matches; the British Isles played games against an East African side, on their 1955 tour, 1962 tours. The national team played its first international in 1955, is yet to qualify for the Rugby World Cup. However, the country's sevens team has had far more international success. Kenya was ranked 39th in the world by the IRB as of 6 April 2009. However, in 2010, Kenya rose in the ranking to 32nd in the world and ranked 31st in 2013 after beating Zimbabwe 29-17 in a tournament that doubled up as the qualifying stage for the 2015 World Cup.

The national sevens team are one of the 12 "core teams" in the IRB Sevens World Series, advancing at least to the semi-finals of three events in the 2008–09 season, reached the semi-finals of the 2009 Rugby World Cup Sevens. They managed to win the 2016 IRB Sevens World Series cup in Dubai; the popularity of Kenyan rugby has increased over the last few years and the country now has over 40 clubs, 40,000 players of which nearly 30,000 are teenagers and 3000 are women. The KRFU oversees Kenyan schools rugby, including the Prescott Cup for the most elite teams, the Damu Pevu shield for the second level of teams. In 1990, Rugby 15s was admitted as formal sport in secondary schools around the country and in 2008 it was admitted as a primary school sport. Rugby Sevens was admitted as a formal sport in secondary schools in 2004. A major part of competition at the junior level is the St Mary's Blackrock Festival, used to scout for Kenya's top players for the last 26 years. Biko Adema, a current Kenya sevens player, was once the most valuable player in the tournament.

The Kenya Cup is the highest level