Clover ( Trifolium ) is a genus of 245 species of plants . It is part of the subfamily of the butterflies (Faboideae) from the legume plant family (Fabaceae). In the parlance however, not only species of this genus are often called "Clover", but also species from the closely related species alfalfa ( Medicago ) and sweet clover ( Melilotus ) and from taxonomically distant species sorrel ( Oxalis ). Characteristic features of the genus are trifoliate leaves and multi-flowered, capid inflorescences . The genus clover is naturally common on all continents with the exception of Australia and Antarctica. Different species of clover were introduced by humans in Australia.
16 different species of clover are used as fodder crops in agriculture . Clover cultivation is of economic importance in both Europe and North America. In Europe, meadow clover ( Trifolium pratense ) was grown as early as the 4th century. Because of its ability to bind nitrogen from the air in symbiosis with nodule bacteria (Rhizobiaceae) on the roots, clover is also important for improving soil fertility .
The shamrock found its way into the symbolism of many cultures. It always represents the trinity, as for example in Christianity as a symbol of the trinity . Furthermore, clover stands for summer or symbolizes love. The four-leaf clover is considered a lucky charm .
Most types of clover are perennial , but a few are also annual (annuelle) and very few biennial (bienne) herbaceous plants . Almost all species branch directly at the base or along the entire stem axis . A few species, however, develop a long, leafless and unbranched stem above a dense cluster of many leaves directly at the base. The stem axis can be upright, lying or creeping. Many species of clover, such as the Caucasian clover ( Trifolium ambiguum ), develop rhizomes . If rhizomes are present, they often make up a considerable part of the dry mass of the plants, in the case of the Caucasian clover this is about 44% of the total mass. The development of foothills (stolons) is less common . It is found, for example, in the white clover ( Trifolium repens ). The density of the hairiness of the plants varies from species to species. The spectrum ranges from densely hairy to almost bald or completely hairless. The orientation of the hair can be flat or protruding. They are directed up or down.
The root system of the clover species is often herringbone-shaped. The shape varies only slightly depending on the substrate , only the number of branches seems to be higher in sandy soils than in clay soils . Annual species have fine fibrous roots, perennial species have thickened, woody roots and rarely even tubers .
As with all legumes, root swellings (nodules) caused by nodule bacteria are typical. The different types of clover have different roots. Trifolium purpureum, for example, has roots up to 2.1 meters deep, whereas the roots of the shield clover ( Trifolium clypeatum ) seldom penetrate deeper than 40 centimeters into the substrate. In ten species examined, the proportion of roots in the dry matter of the plants was between 14% and 30%.
The leaves are usually alternate . In some species the upper leaves appear opposite ; here the upper nodes are so close together that it gives a false impression of objectivity. In this case, however, one of the two leaves is often not fully developed. The leaf blades are pinnate in almost all species . Only species of the subsection Lupinaster in the section Lotoidea have five to nine fingered leaves.
The lower (basal) leaves often differ significantly in size and shape from the upper leaves. The leaflets here are often ovate, obovate or broadly elliptical, they are always much wider than the leaflets of the upper leaves. The feather shape is a relatively stable feature. However, it can vary to a small extent both within an individual and within a species . The leaf margin has entire or fine to coarse serrations. The blade is hairy on both sides or only on the underside of the leaf, but also glabrous in some species. The leaf nerve is uniform within the species. The secondary leaf veins branching off from the main rib run approximately parallel. They or their branches reach the edge of the leaf.
The shape of the stipules is also strongly conserved (uniform) within certain groups. The spectrum ranges from narrow and sharply pointed in the upper half to broadly elliptical. They have entire margins in all sections except involucre and paramesus , in these they are toothed or deeply incised with lanceolate lobes. In the species of the African sub-section Ochreata , the petioles of the deciduous leaves are fused with the stipules over their entire length and the internodes are thus covered. Similar adhesions, however, only in the petioles of the upper leaves and not as pronounced, exist in other species as well.
The inflorescences are usually axillary and stalked or, very rarely, sessile. In a few species, however, they are also terminal. Mostly they are head-shaped and multi-flowered. Inflorescences with a few individual flowers are the exception.
The Israeli botanist Michael Zohary examined the shapes of the inflorescences in the Lotoidea section in 1972 . There it was found that almost all species develop panicle-like inflorescences, but there is a tendency towards spike-like inflorescences. Evolutionarily more developed species also seem to form shorter flower stalks. However, it is unclear whether these results are representative of the entire genus.
Bracts are found mainly in the more primitive sections of the genus, always together with panicle-like inflorescences. Altogether two different evolutionary trends can be recognized in the genus: on the one hand the regression to bract rudiments or the complete disappearance of bracts and on the other hand the aggregation of bracts directly under the head, which leads to involucral formation ( bracts ). There are pronounced bracts, for example, in the section Mistyllus , which is one of the evolutionary primitive sections of the genus. The bracts are rudimentary or absent, for example in the trifolium section , bracts can be found, for example, in the involucrarium section .
The calyx in the genus Klee is mostly symmetrical and tubular or bell-shaped with five almost uniform calyx lobes or teeth. Three variations of the calyx are common: In the species of the subsections Loxospermum , Calycospatha and the section Mistyllus , the calyx tube is blister- shaped. In some other species, especially in the Chronosemium section , the upper two calyx teeth are shortened compared to the three lower ones. Finally, in the trifolium section, there are often closed calyx tubes.
Shamrocks are five-fold butterfly flowers . The crown varies in color from pure white to yellow to dark purple. Two-tone crowns are common. Often the color changes after the anthesis (process of flowering) and the inflorescences appear multicolored. The four lower petals (boat and wing) are loosely fused and attached to the stamens . The fifth petal (the flag) is free and enlarged. The wings are usually much longer than the shuttle. The stamens are ten in number, nine of them are fused to form a U-shaped tube. At the base of the tenth, upper, free stamen there is a small nectar gland . In some species there is a tendency to reduce the number of pollen sacs per stamen, such as Trifolium badium , T. repens , T. campestre and T. dubium ; in a flower there are stamens with the normal four, but also three and two pollen sacs, whereby the ventral pollen sacs are reduced in each case. The ovary lies within the tube from the stamens. The crown usually falls off prematurely and is only preserved in some species. In the mistyllus section, the remaining crown dries up. Only in the Chronosemium section does it support the blowing away of the seeds ( wind pollination ).
The pollen grains of the genus are prolate, which means they have the shape of ellipsoids of revolution . The exine, i.e. the outer layer of the sporoderm (the wall of the pollen grain), are tricolporate, that is, it has three elongated germinal folds (colpi), in each of which there is a rounded germinal pore (porus). The pollen grains are 14 to 35 micrometers in diameter. They are 21 to 49 micrometers long and have a length to diameter ratio between 1.19 and 1.64.
The smallest pollen grains are found in the small-flowered clover ( Trifolium retusum ) and the small-flowered clover ( Trifolium suffocatum ). The largest pollen grains were observed in the meadow clover ( Trifolium pratense ). In some American species, such as Trifolium albopurpureum , the pollen grains are almost spherical. The surface structure (sculpture) of the pollen grains varies greatly within the genus.
As the original fruit form of the genus, many-seeded legumes that tear at two seams are considered. Within the genus there is this archaic fruit type as well as many evolutionarily derived forms that are increasingly approaching the closing fruit . In the Lotoidea section , in which most of the primitive evolutionary characteristics of the genus are preserved, there are a number of species, such as the bird's foot clover ( Trifolium ornithopodioides ) or the western alpine clover ( Trifolium alpinum ), with such typical, many-sampled pods that burst open at two seams. From this initial form many derived forms exist: in the extreme case, a hose-seeded (utricle) or nutlets with a very thin pericarp (pericarp), which in some cases even only from epidermal cells (final tissue) consists. In these extremely reduced pods, the seam is missing, and so the fruit can no longer tear, but divides transversely or irregularly. Such fruits are mainly found in the Trifolium section , for example in the spreading clover ( Trifolium diffusum ), but also in many other sections and even in Lotoidea .
An intermediate form is the single-seeded sleeve, in which both seams are present. Fruits of this form are found, for example, in the Usambara clover ( Trifolium usambarense ), in Trifolium burchellianum but also in many other species. Another intermediate form is the single-seeded sleeve with only one seam. This type of fruit can be found in several sections, but is rather rare.
The shape of the seeds is typically egg-shaped, ellipsoidal or oblong-ellipsoidal and laterally compressed, but varies in dimension, weight and shape. Variations of the form resulting from the differing position of the hilum , the insertion of the umbilical cord (funiculus) through which the seeds with the ovary is connected. In the embryo, the hilum separates the root system (radicula) from the cotyledons (cotyledons).
In some species, for example in the three subsections Lotoidea , Oxalioidea and Ochreata in the Lotoidea section , the hilum is terminal. Here the root system and the cotyledons are almost the same length. In almost all other species, the hilum is on the side or on the edge. Then the root system is significantly shorter than the cotyledons. The seed coat (testa) can be smooth, roughened, warty, wrinkled or granular. The surface structure of the Testa does not seem to correlate with the taxonomic classification of the genus.
About 70% of the species in the genus were examined for the number of chromosomes . The species are usually diploid , i.e. contain two sets of chromosomes per cell. However, other degrees of ploidy also occur. Polyploidy , or polyploidy and diploidy in two lines side by side, occurs in 38 species . Of these, 31 are perennial, but only seven are annual.
The base number, i.e. the number of chromosomes in a single set, is 8 for 80% of the species examined, 7 for 15% of the species, 6 in 2% and 5 in 3% of the cases. The base number 8 also seems to dominate the other species of the Trifolieae tribe . Reduced chromosome numbers and aneuploidy , which means that individual chromosomes are present or missing in addition to the usual set of chromosomes, are particularly common in the Trichocephalum and Trifolium sections . This is another indication that these sections are more derivative forms than the others.
The shape of the chromosomes was studied in 14 African and 15 European diploid species. There were one to three pairs of metacentric chromosomes ( centromere in the middle), four to six pairs of submetacentric chromosomes (centromere between middle and end) and one pair of acrocentric chromosomes (centromere at the end, the shorter arm very small).
The genus clover is very widespread and is represented in a total of four flora kingdoms, the Neotropic , Paleotropic , Holarctic and Capensis . However, the genus is absent in the Australis . The range can be divided into three distinct centers: Eurasia, Africa and America.
About 59% of all species are native to Eurasia . The center of diversity , i.e. the area with the highest biodiversity (a total of 110 species from seven sections), is located in the Mediterranean region . In the Euro-Siberian and Turanian- Iranian areas, however, only 8% of the species together are found. Some endemic species exist in almost every Mediterranean country . However, most endemic species are found in Turkey, with a total of nine endemic species out of the 100 naturally occurring there. The northern border of the distribution area runs through Sweden and Norway and reaches about the northern polar circle . To the east the natural biodiversity decreases and only the two species Trifolium lupinaster and Trifolium gordejevi can be found in the Far East of Russia , on Sakhalin and in Japan.
15% of all species are common in Africa. The majority of the species found in North Africa are native to the Mediterranean area, as in Europe. There are only two endemic species here, both in the Atlas Mountains . Half of all North African species are also found on the Macaronesian Islands . Almost all non-European species are found in the highlands of Abyssinia . Klee is absent from the Arabian Peninsula , with the exception of the Yemeni highlands. The distribution area continues as far as the Cape in the very south of Africa, although clover is only found here in the tropical highlands and is absent in the lowlands. Clover is absent in Madagascar , Namibia , Botswana and the Sahel . The only species that reaches the northern edge of the Sahara is the felt clover ( Trifolium tomentosum ).
The remaining 26% of the species are common in America. In North America, clover is absent in Alaska and almost all of Canada; in the United States, it is absent in the northeast. The manifold center is in California . In the south the distribution area extends to about 43 ° south latitude in South America. Even in the tropics of America, the clover is only found in the highlands and is absent in the lowlands. Clover is absent from the West Indies , Panama and Guyana .
In addition to the native species, there are also many neophytes, especially in North America. Of the ten species described by Jan Frederik Gronovius in the Flora Virginica in 1739 , nine turned out to be introduced. In 1994, 93 species of clover were known from the United States, 64 of which are naturally occurring there and 29 are neophytes.
In Australia, too, where clover does not occur naturally, many species are neophytic. In South-West Australia, for example, 35 neophytic species of clover are counted. However, introduced clover is also found in the alpine regions of Eastern Australia. A total of ten species are classified as invasive . Klee was also introduced to New Zealand and Hawaii.
The genus Klee is native to extremely diverse habitats . The distribution area ranges from subarctic regions, through areas with mesian conditions (areas of medium humidity), through subtropical to tropical regions. However, around 75% of American, 87% of African and 50% of European species are restricted to mountainous locations at altitudes up to 4,000 meters.
Like the other legumes, Klee lives in a mutualistic symbiosis with nodule bacteria (Rhizobiaceae). These have the ability to bind elemental, molecular nitrogen, i.e. to convert it into compounds and thus make it biologically available.
In contrast to other legumes, bacteria are often found in clover that have specialized in certain types of clover and cannot establish a successful symbiosis with other legumes. In this case, one speaks of biovars. This applies in particular to bacteria of the genus Rhizobium . For example, the meadow clover ( Trifolium pratense ) only enters into a symbiosis with Rhizobium trifolii , whereas the white clover ( Trifolium repens ) , for example, also lives symbiotically with Rhizobium leguminosarum .
The clover species have typical butterfly flowers for insect pollination ( entomophilia ). The flowers are mainly visited by insects with long proboscis , such as honey bees ( Apis ), bumblebees ( Bombus ) and some butterflies (Lepidoptera). They collect nectar and pollen there. When the visiting insects exert pressure on the flag and wings primarily with their heads, the stigma and anthers are stuck out of the boat and pressed against the underside of the insect's head. This is how pollination can take place. If the pressure on the flag is released, the stigma and anthers return to their old position in the shuttle. The pistil is usually longer than the stamens and slightly curved. The anthers are open, even in the bud. Nectar is excreted at the bottom of the corolla tube.
A white clover flower ( Trifolium repens ) produces on average between 0.02 and 0.08 microliters of nectar with a sugar concentration between 42 and 65%. In cultivated species, this proportion averages between 22 and 66%.
Most species of clover are allogamous, that is, pollination occurs through cross- pollination . The highest fertilization rate is achieved with pollen from another plant of the same species ( xenogamy ). With the meadow clover ( Trifolium pratense ), fertilization takes place between 18 and 50 hours, depending on the temperature, after pollination. A relatively high humidity of 93 to 98% is essential for good pollen formation. However, some species are autogamous (self-pollinating). Here, however, the proportion of successful fertilizations is lower. A few species are even cleistogamous , that is, the flowers do not open at all during anthesis.
- Telechory is the type of spread in which the seeds are spread over long distances, for example by wind or animals. This is the usual way of spreading within the genus Klee with the following characteristics:
Anemochory , the spread by wind takes place in light fruits, in some cases the calyx has additional outgrowths similar to a pappus . These outgrowths can be feathery (for example in the hare clover ( Trifolium arvense )), winged (for example in the field clover ( Trifolium campestre )) or vesicular (for example in the Persian clover ( Trifolium resupinatum )).
In some species, the entire fruit cluster is blown away (for example in the felt clover ( Trifolium tomentosum ) or in the Trifolium bullatum ). In other cases, the fertilized flower is blown away, with the crown being transformed into a spoon-shaped or boat-shaped flying machine. Here the seed then ripens in the already separated flower. This strategy can be found, for example, in the Chronosemium section .
- Epichory , that is the spread by animals, is only used by a few species. For example, the calyx teeth of the small-flowered clover ( Trifolium retusum ) or rough clover ( Trifolium scabrum ) like to get caught in the fur of animals.
- Anemochory , the spread by wind takes place in light fruits, in some cases the calyx has additional outgrowths similar to a pappus . These outgrowths can be feathery (for example in the hare clover ( Trifolium arvense )), winged (for example in the field clover ( Trifolium campestre )) or vesicular (for example in the Persian clover ( Trifolium resupinatum )).
- Amphicarpy is a special case that is only found in Trifolium polymorphum . The species forms two different fruits. The upper inflorescences produce light fruits that are carried away by the wind, while the lower inflorescences curve downward and deposit the seeds on the ground. So topochory and telechory are combined.
- Topochory is the phenomenon that the seed or fruit remains close to the mother plant. The following manifestations can be found in clover:
- Barochory means the simple fall of single, bare and heavy seeds by gravity from a fruit that tears open at the seams and remains on the mother plant. To do this, the pod bends down when the fruit is ripe. This mechanism is particularly common in the subsections Lotoidea , Loxospermum and Falcatula .
- Under Calycobolie the phenomenon is meant in which the cup enclosing the fruit breaks in the fruit ripening of the rachis and the whole fruit falls to the ground. Here it can be blown away or remain with heavy fruits. This method is found in many species of the Mistyllus , Trifolium and Vesicaria sections .
- In synaptospermia , it is not a single fruit that falls down, but the entire inflorescence with several fruits. To do this, he breaks off the stem axis. These pods are usually too heavy to blow away. Synaptospermia is found in the sections Mistyllus and Trichocephalum , but also in species in the Trifolium section , such as Cherler's clover ( Trifolium cherleri ) or Trifolium scutatum .
- In aestatiphoria , the fruit does not fall at all until the plant disintegrates. Here the fruit remains closed. This phenomenon exists, for example, in the hedgehog clover ( Trifolium echinatum ) or in Trifolium latinum .
- Basikarpie is the case in which the heavy fruits press the inflorescence to the ground and germinate there. This occurs, among other things, in the small clover ( Trifolium suffocatum ).
- Finally, geocarpy is found in two species of the Trichocephalum section . Here some sterile flowers are transformed into drills that enclose the fertile flowers and penetrate the soil. There the fruits ripen and the seeds can germinate. The species Trifolium batmanicum and Trifolium chlorotrichum can also produce underground fruits. Here, however, no drilling apparatus is formed, but the inflorescence axes grow long downwards.
Parasites and pathogens
The clover silk ( Cuscuta epithymum subsp. Trifolii ), for example, is a chlorophyllless plant without leaves that parasitizes on clover. The reddish stems of the clover silk wind around the clover plant and penetrate with so-called haustoria into its conduction tissue ( phloem ) and deprive it of the nutrient solution necessary for growth.
The clover strangler ( Orobanche minor ) is a 10 to 40 centimeter high plant that mostly parasitizes on meadow clover ( Trifolium pratense ) and the middle clover ( Trifolium medium ). If the root of the clover strangler reaches a clover root, it penetrates it and, like the clover silk, forms a haustorium through which it removes the nutrients from the clover.
Kleeälchen ( Ditylenchus dipsaci ) are a type of roundworm (Nematoda). They can penetrate the shoot axis of young clover plants underground, or above ground in the event of flooding, and feed on them. Affected parts of the plant become withered and fall off.
The northern stem burner ( Kabatiella caulivora ) and the southern stem burner ( Colletotrichum trifolii ) are other mushrooms that specialize in clover. If the plant is infected, they cause black discolored lesions on the stems and leaves.
The German word Klee , originally mainly for Trifolium pratense, from Middle High German klē , goes back to the Old High German klēo (10th century), whereby the “o” developed from the original “w” of the stem end ( Old Germanic * klaiwaz ) . In other Germanic languages , the "w" was largely retained. It is called in Low German Kliev , (scenic) Klever , Dutch (dialect) klaver and Old English clāfre , clǣfre , from which the English clover developed. Loan words prevail in the other Germanic languages.
The ancient Germanic plant name * klaiwaz is an extension of the Indo-European root * gleiH - 'glue, lubricate'. It remains to be seen whether the plant genus is named for its sticky sap (especially the flowers) or for its ability to take root quickly (cf. Old High German klīban , 'to stick, stick, stick').
The scientific name of the genus Trifolium was chosen by Carl von Linné on the basis of the pre- Linné name of a group of plants, under which not only most of the species of the current genus, but also a whole range of other clans such as today's fever clover ( Menyanthes trifoliata ) or many species the current genus wood sorrel ( Oxalis ) were subsumed. The origin of the name is probably the Latin trifolium , which was used for clover by Pliny the Elder . It is a loan translation of the ancient Greek τρίφυλλον triphyllon , which is mentioned by Herodotus in section 132 in the first book of his histories, later also by Pedanios Dioscurides .
A plausible explanation for this name would be the combination of the Latin tri , which corresponds to the Greek τρι, tri , and means three and folium , φύλλον, phyllon which means leaf . However, it is noticeable that such a well-known and widespread plant genus in southern Europe, which was also used as a forage plant in ancient times, is only sparsely mentioned in the ancient sources. Other species from the same tribe, on the other hand, appear much more frequently in ancient literature. For this reason, some authors advocate the theory that triphyllon was actually not a clover, but a different genus or species with three-part leaves, such as the asphalt clover ( Bituminaria bituminosa ).
Most of the original features of the species in the Lotoidea section have been preserved. The section is therefore considered to be the oldest and most evolutionarily primitive section of the genus. Zohary assumes that all other sections developed directly from the lotoid .
It is unclear where the genus originated. Jan Bevington Gillett assumes that the genus originates from the Mediterranean region. This follows from the manifold center in this region. Another theory says that the genus originated in the highlands of East Africa and only came to Europe later. An early examination of the chromosome shapes supports the latter thesis. Zohary believes that there could have been two origins in Europe and Africa where the clover was made at the same time.
It is unclear how the genus reached North America. A migration via the Bering Strait or the Pacific appears unlikely, since only two species are found in the far east of Russia and they only sparsely populate the region. A migration movement from Europe is also unlikely, as the diversity center of the genus in North America is on the west coast. It is also not clear how the genus was able to spread so far in the north-south direction in America and Africa, over sometimes considerable gaps.
The genus clover was already well known to the ancient naturalists. Theophrastus of Eresos believed it to belong to the horn clover ( lotus ). Pedanios Dioscurides meant the asphalt clover ( Bituminaria bituminosa ) with his triphyllon . Pliny also mentioned the genus.
In the pre-Linnean period, clover was mainly mentioned as a fodder plant. Leonhart Fuchs described and illustrated a total of seven species of clover in his New Kreüterbuch in 1543 , four of which are still part of the genus today. William Turner described five species under the name Trifoly in his book The names of the herbs in 1548 , one of which still belongs to the genus. John Gerard even dealt with 21 species of clover in his work The Herball or Generall Historie of Plantes in 1597 , of which 10 still belong to the genus today. Klee is also found in Clusius (1601, 7 species) and Bauhin (1620, 24 species). It was Bauhin in his second book Pinax theatri botanici 1623 who first tried to divide the genus into subgroups (there are eleven in his case). His brother Johann Bauhin was the first to separate the genus snail clover ( Medicago ) from trifolium in 1651 together with Johann Heinrich Cherler , but still mixed it with the genera horn clover ( lotus ) and sweet clover ( Melilotus ). Other authors of this time who deal with the clover are Robert Morison (1680, 45 species), Rivinus (1690–1699), Plukenet (1696) and Tournefort (1700, 44 species). Pier Antonio Micheli named the genus Trifoliastrum in 1729 and divided it into seven groups. These seven groups are not dissimilar to the current division into sections of the genus. In 1739 Jan Frederik Gronovius described ten species of clover from North America in his Flora virginica , but only one of them occurs naturally there and the other nine were already introduced. Also Adriaan van Royen tried together with Albrecht von Haller , a division of Clover subgenres, this was but less accurate than that of Micheli.
The main problem of all these authors was the clean separation of the genus sweet clover ( Melilotus ) from the clover ( Trifolium ). Even Carl von Linné himself did not succeed in this completely. He included the genus Melilotus as the group Trifolium Melilotus in the genus Trifolium .
According to Linnaeus, species of the genus were found in almost every published local flora. The article on Flora Orientalis written by Pierre Edmond Boissier in 1872 is noteworthy , in which he already listed 113 species and divided them into clearly delineated sections that almost completely correspond to the current classification.
Despite the innumerable mentions of the species in the literature, there have been few monographic treatises of the genus. The earliest is by Nicolas Charles Seringe in 1825, in which he covered 150 species (including some North American species). In 1832, Karl Bořiwog Presl divided the genre into nine separate genres. The botanical community, with the exception of Bobrov , rejected this. Karl Heinrich Koch, probably ignorant of Presl's work, divided the genre into sections that almost coincided with Presl's division. Ladislav Josef Čelakovský tried in 1874 to rewrite the previously described sections of the genre, but was not very successful. The first key of the genus already contained 211 species and was published by Francesco Lojacono in 1883 . He divided the genus into two sub-genera, Trifoliastrum and Lagopus , but this appeared unnatural and was rejected by other botanists. In 1967, Bobrov created eleven independent genera analogous to Presl and even founded a separate tribe Lupineae for some of these genera. However, this classification was ill-founded and does not correspond to today's doctrinal opinion. Michael Zohary and David Heller published a large monograph of the genre in 1984. This extensive work is divided into a general and a taxonomic part. The latter was highly praised and contains 237 species, which are divided into the current eight sections. However, the general part is considered to be weaker and, in particular, as incorrect in terms of dissemination information. John Montague Gillett published another monograph of the genre in 2001 together with Norman L. Taylor . This has only a very rudimentary general part and does not contain any taxonomic classification of the species, rather 228 species are illustrated and described. In addition to these monographs on the genre, a large number of monographs on individual sections have been published.
The tribe Trifolieae contains five or six genera and is divided into three subtribes. The genera that, in addition to the clover ( Trifolium ), certainly belong to the Trifolieae are Trigonella , snail clover ( Medicago ) and sweet clover ( Melilotus ). The status of the genera Parochetus and Restharrow ( Ononis ), which play a special role, is not certain . Zohary still counted the genus Factorovskya to the tribe, but this was transferred in 1984 to the genus Snail Clover ( Medicago ).
From a morphological point of view, the genera Trigonella , Medicago and Melilotus are classified in the one subtribe Trigonellinae , whereas Trifolium is the only genus in the subtribe Trifoliinae. A separate subtribe Parochetinae was created for the unclear genus Parochetus , whereas Ononis was placed in its own tribe Ononideae.
However, recent molecular genetic studies show a slightly different picture. The close connection of the tribe Trigonellinae is first confirmed. Medicago is monophyletic and sister taxon to Trigonella . Melilotus, on the other hand, is nested with Trigonella ( paraphyletic ). According to this investigation, Trifolium is closer to the tribe of the Fabeae (formerly known under the name Vicieae ), consisting of the sweet peas ( Vicia ), the lentils ( Lens ), the peas ( Pisum ), the flat peas ( Lathyrus ) and the genus Vavilovia , related to the Trigonellinae. Likewise, the genus Ononis is more closely related to the Trigonellinae than to Trifolium , whereas Parochetus is very far from these species. An even more recent study confirms these results. Then the following cladogram would result:
After the monographic processing of the genus by Michael Zohary and David Heller in 1984, it comprises 237 species, nine species have been newly described since then, one of the species status revoked, so that 245 species are currently assigned to the genus. Zohary divides the genus into eight sections according to morphological characteristics:
- With 99 species in America, Africa and Eurasia, the Lotoidea section is the largest section of the genus and the most taxonomically difficult. The species are so heterogeneous that the section has been divided into nine subsections and 13 series. Especially the classification of the American species is difficult. The main characteristics of the section are: umbrella-like inflorescence, stalked flowers with bracts and two- to many-seeded legumes. The section is considered to be the most evolutionarily primitive section of the genus.
- The Paramesus section with only two species in Eurasia is controversial. Some authors suggest including them in the Lotoidea section . Characteristics are the glandular teeth on the stipules and on the calyx.
- The section Mistyllus with nine species in Africa and Eurasia is clearly distinguished from the other sections by the structure of the symmetrical, bubble-shaped calyx and the persistent crown, which is unique for clover.
- The section Vesicaria with seven species in Eurasia is clearly differentiated from the other sections by the structure of the asymmetrical, bubble-shaped calyx, which is unique for Klee. The upside-down flowers can also be found exclusively in this section.
- The Chronosemium section with 19 species in Eurasia is clearly different from all other sections. Features are the eye-catching two-lipped calyx, the persistent crown with a spoon- or boat-shaped flag and the solitary fruits.
- The Trifolium section is the second largest section of the genus with 74 species in South Africa and Eurasia. It is divided into 17 relatively small but natural groups, which are described as subsections. The flowers are sessile here and without bracts. The corolla tube is often hairy and the fruits are solitary without seams.
- The Trichocephalum section with nine species in Eurasia differs greatly from all other species in the fact that most of the flowers are sterile and are transformed into hairs or bristles for seed dispersal.
- The Involucrarium section with 26 species only in America is differentiated from the other sections by the shape of the calyx teeth, the teeth on the stipules and the pronounced bracts.
A molecular genetic investigation from 2006 showed that a division into two subgenera Chronosemium and Trifolium with eight sections is probably justified. In this case, the Lotoidea section would be torn and the Mistyllus and Vesicaria sections merged. So far, the sub-genera proposed after this investigation have not yet been validly described.
The species of the genus Trifolium and their assignment according to Zohary and Heller are:
In Appendix I of the CITES Convention and in the Red List of Threatened Species of IUCN contained no clovers. However, some species are endangered by loss of location. The Fauna-Flora-Habitat Directive (FFH) of the European Union lists stone clover ( Trifolium saxatile ) as endangered.
Several species of clover are listed in the Red Lists of the individual German federal states, but Appendix 1 to the Federal Species Protection Ordinance does not contain any species of clover. The Red List of Switzerland lists the strip-clover ( Trifolium striatum ) as "high risk" ( endangered ) and five species ( Trifolium spadiceum , saxatile T. , T. patens , ochroleucon T. and T. fragiferum ) and some subspecies as " endangered "( vulnerable ). In Austria, Trifolium retusum is considered critically endangered, Trifolium spadiceum and Trifolium striatum as critically endangered.
The status of individual clover species in other regions is difficult to assess, and most areas are not known to be endangered.
The first traditions about clover cultivation concern the Near East and come from the time of early Christianity. The Hebrew name for clover תלתן, tiltan also appears in the Mishnah , but it is not certain whether plants of the genus Trifolium are really exclusive here . In Europe, meadow clover ( Trifolium pratense ) was first grown from the 4th century AD.
The cultivation of clover as a useful plant for rational cattle breeding in Europe began around 1780, initially in Saxony and Austria as well as in southern Germany, especially after Johann Christian Schubart's agricultural research .
In 1953, 15 species of clover were grown commercially; in 2001 there were 16, with the same species being cultivated in North America and Europe. They are mainly used as animal feed and can be used as green fodder as well as ensiled or dried to make clover hay . Clover is mainly fed because of its high percentage of digestible protein.
Because of its ability to bind nitrogen from the air in symbiosis with nodule bacteria, it also serves to maintain soil fertility . Particularly important is the cultivation of red clover ( Trifolium pratense ) as a cover crop for arable crops such as maize ( Zea mays ) or wheat ( Triticum ), in which if crop rotation are switched perennial Ansaatwiesen between. The clover binds atmospheric nitrogen in root nodules and thus returns nutrients to the soil in a natural way. This reduces the consumption of nitrogenous fertilizers on sowing meadows by two thirds. As a result, less of it gets into the water.
More rarely, clover is also grown as a beehive plant and on a very small scale as a culinary herb and for medicinal purposes. Various types of clover, such as thread clover ( Trifolium dubium ), have a hemostatic effect , while other types can help with menstrual cramps due to the phytoestrogens they contain or use to increase the amount of milk when breastfeeding . Meadow clover ( Trifolium pratense ) is also said to help with skin diseases and is used in traditional Chinese medicine to treat cancer .
The use of clover as a fodder plant in the German-speaking area was successfully propagated around 1781, especially by Johann Christian Schubart . In Franconia , Philipp Adam Ulrich had a decisive influence on clover cultivation as early as the first half of the 18th century.
Clover cultivation is widespread across Europe and North America. However, it also extends around the whole of the Mediterranean Sea, including the neighboring African countries, as far as Asia. Clover is also grown to a considerable extent in Australia and New Zealand. In Central Africa, mainly other legumes and hardly any clover are grown.
Clover can be grown in the main crop as a pure seed without a partner, or together with grasses as a cover crop ( clover grass , often with winter rye ). In addition, clover can be grown in winter catch crops alone or in a mixture as undersown . As the main crop with or without grass clover, an average yield of 250 decitons of green matter per hectare is achieved, but under optimal conditions and with intensive fertilization, yields of up to 500 dt / ha of green matter are possible. When cultivated as a winter catch crop, the average green matter yield is 135 to 190 dt / ha.
The meadow clover ( Trifolium pratense ) is the most important type of clover, measured in terms of the area under cultivation and its importance for feeding . White clover ( Trifolium repens ) is often sown on grassland , where it significantly improves the nutrient content of the forage. On light soils, it is often combined with ball of grass ( Dactylis ).
Other types of clover that are important for agriculture are Egyptian clover ( Trifolium alexandrinum ), Persian clover ( Trifolium resupinatum ), Swedish clover ( Trifolium hybridum ) and incarnate clover ( Trifolium incarnatum ), the latter mainly as part of the Landsberg mixture .
In order to increase the yield, crosses between different species were also created and tested. A hybrid Trifolium repens × nigrescens of white clover ( Trifolium repens ) and black-growing clover ( Trifolium nigrescens ) is successful and has meanwhile become economically important . Trifolium repens × ambiguum from white clover and Caucasian clover ( Trifolium ambiguum ) is also grown .
Clover as a poisonous plant
Clover species are valuable forage crops, but depending on the season, the weather and the amount fed, they can cause damage to animals. Cattle are endangered by clover species, especially if they are excessively fed or if the clover is wet.
Many species of clover can cause phototoxic reactions in animals due to the thiocyanates (inorganic salts) they contain and lead to hypersensitivity to light. This condition is called trifoliosis or clover disease. It manifests itself in reddened and swollen eyelids and lips, and other unprotected areas of the skin can also be affected. Trifoliosis occurs mainly in horses, cattle and sheep.
In cattle, clover can also lead to the accumulation of gas in the rumen ( rumen tympany ) through foamy fermentation of soluble, cytoplasmic proteins . Cyanogenic glycosides contained in clover , especially linamarine and lotaustralin , can block the respiratory chain and lead to cramps. Phytoestrogens , especially various isoflavones such as genistein or formononetin from clover, can lead to fertility disorders.
The three-leaf clover has always been a symbol of trinity. In the Persian Empire of late antiquity it stands for the triad of gods ( triad ) of Mithra (Mihr) next to Ahuramazda (Ohrmazd) and Anahita (Anahid). With the pre-Christian Celtic Druids , the clover was considered a sacred symbol and magic plant.
In Christian symbolism, the shamrock was adopted early on as a symbol of the Trinity and is often found in pictorial representations. It became the symbol of Saint Patrick of Ireland , who allegedly declared the Trinity to the Irish using a shamrock. Another attempt at explanation, however, leads the symbol of the cross stick with its clover-leaf-like upper end, which St. Patrick thrust into the throat of a snake. In Ireland the shamrock is called the shamrock . The oldest surviving manuscripts that mention it as sheamair or sheamrach date back to 1571. Even today it is a symbol of the Irish-Celtic national consciousness.
As a medicinal plant, the clover was assigned to Mary , Mother of God, in the Middle Ages . Since clover was often planted on graves in the Middle Ages because of its fresh green, probably also as an indication of a life after the resurrection, it also became a symbol of farewell. For example, in his description of the Swabian War, Johannes Lenz lets the army go through the "green clover" before the bloody battle:
"Through loub gras, through the green cley
in quiet breeding on everything screamed"
Klee as a symbol of love
In connection with roses, the symbol of love, and with violets, because of the violet color of penance, the clover is also used as a symbol of love. For example, Isolde wears a Schapel (hoop-shaped headdress) made of clover when she meets Tristan in Gottfried von Strasbourg's Tristan und Isolde .
“A Schapel carried them from Klee. To
her master more than ever
she seemed lovely, delightful. "
In the new Germans Parnass by Johann Rist clover is associated with the phrase "singing from the beautiful Galathée". According to an old legend, an artist falls in love with his self-made statue of the nymph Galathée , which made her a symbol of love.
"There they count the sheep in their yellow clover
and soon afterwards they sing a song from Galathe"
More important in medieval love poetry is the green clover as a place of love encounter and rendezvous . In this context, it is about in the verdant youth superfluous thoughts of Christian Weise used. As a symbol in this meaning, clover is also popular with many other poets, especially after the 16th century.
"And were allowed to rest together in the clover"
Praise and exaggeration
The popular phrase " praising someone on the green clover " is used to mean unduly praising the praised one. Originally, this phrase meant that greater life force was ascribed to the one who was promised. In love poetry and fairy tales of the Middle Ages, the image of the green clover as the epitome of freshness and vitality was widespread and can be found, for example, in Grimm's fairy tale The Four Artful Brothers ( KHM 129).
"'Yes', said the old man to his sons, 'I must praise you for the green clover, you have used your time and learned something righteous'"
Today's expression probably refers to this poetic praise of the clover in the Middle Ages, which in later times appeared to be exaggerated, so that something that went beyond that had to be understood as a grotesque increase.
Clover as a symbol of spring and summer
Even in Chinese symbolism , the shamrock is a symbol of summer. Also in our culture it is often used as a spring or summer symbol because of its strong green color, for example by Ewald Christian von Kleist in his poem Der Frühling :
"A carpet adorned with tendrils and foliage, of
bushes, flowers and clover, undulates on fields and meadows"
In folk songs, perhaps because of the happy rhyme of “snow, clover and woe”, snow and clover are often used as a pair of opposites. The snow then means winter and suffering, whereas the clover stands for summer and love. Examples are There was a mother who had four children or Good night :
"In the summer the clover grows,
In the winter, the snow snows,
I come again"
The four-leaf clover
In Christian symbolism, the four-leaf originally represents the cross and the four gospels . However, it has always been considered a sign of good luck. This is probably not only due to its rarity, but originally to the vigorous, vital growth of these plants. Legend has it that when she was expelled from paradise , Eva took a four-leaf clover with her and thus embodies a piece of paradise.
The four-leaf clover was already considered an effective remedy against evil spirits by the Druids in Celtic times. John Melton satirized the superstition in the four leaf already in his satire Astrologaster . Probably this is the first written mention of four-leaf clover as a symbol of good luck:
"If a man walking in the fields find any four-leaved grass, he shall in a small while after find some good thing."
"If a man finds any four-leaf grass while walking through the fields, he will find something good shortly afterwards."
In addition to four-leaved leaves, there are also leaves with more than four leaflets, albeit more rarely. According to the Guinness Book of Records , the record since 2009 has been a 56-leaf clover. True four-leaf clover are mostly found on white clover ( Trifolium repens ). There are no reliable studies on their frequency. However, collectors report a rate of around one in 10,000. A study carried out in Munich from 1979 to 1986 suggests a ratio in favor of the three-leaved between 20 to one and 60 to one. The kind of lucky clover ( Oxalis tetraphylla ), which is occasionally found in the trade (especially at the turn of the year), belongs to the genus of wood sorrel ( Oxalis ) and is not a real clover.
Illustrations of clover leaves are also popular in heraldry . Here they are a mean figure . Both the four-leaf and the three- leaf clover appear as a motif. Examples of the use of the three-leaf variant are the coat of arms of the municipality of Cleebronn , the municipality of Hitzhofen , the coat of arms of the Ehmen district or that of the former Berlin district of Tiergarten in Germany, Viktorsberg , Kirchbach , Angerberg or Schönwies in Austria and Berikon or Löhningen in Switzerland. There are also clovers in the coats of arms of various noble families , such as Carlowitz or Bodewitz .
The coats of arms of the cities of Fürth and Kassel are very well known . In the Fürth coat of arms, the origin of the three-leaf clover is not exactly clear, but the trinity probably goes back to the triple rule of the Dompropstei Bamberg , the margraviate of Ansbach and the imperial city of Nuremberg via Fürth during the Middle Ages. The clover leaf was also used in the club crest of the game association Greuther Fürth . The meaning of the 13 clovers in the coat of arms is also controversial in the Kassel coat of arms. The coat of arms of Hanover shows a Mary flower and not, as is often wrongly claimed, a clover leaf. Examples of the use of the four-leaf variant are the coat of arms of the municipality of Brest and the municipality of Brinkum as well as the coat of arms of SC Rot-Weiß Oberhausen and the Scottish club Celtic Glasgow .
In Ireland, the three-leaf clover, the shamrock , is a national symbol alongside the harp. Aer Lingus , Irish Ferries and others use the shamrock as their company logo. Despite the reference to the legends of St. Patrick, it is only mentioned in scriptures 1000 years later in 1751. It has only been worn on St. Patrick's Day since the 17th century instead of the previous Patrick's cross. In 1798 it became a symbol of the Irish Revolution . Ireland also had the shamrock protected by law. This trademark protection was first successfully challenged by a German company in the 1980s, but was confirmed again in the appeal in 1985.
One type of motorway intersection is called a clover leaf because of its oversight . It is the most common type of motorway junction in Germany. It consists of four tangential (ramps) and four radial lanes, the so-called ears.
The trefoil (English: clover, trefoil ) said warning symbol for radioactivity and ionizing radiation is reminiscent of a clover leaf. It was designed at the University of California at Berkeley in 1946 .
In Scandinavian countries in particular , but also in the Baltic States , a four-leaf clover is a political symbol of peasant-liberal center parties (see Finnish Center Party , Norwegian Center Party , Swedish Center Party , Estonian Center Party ).
The National Board of Boiler and Pressure Vessel Inspectors (NBBI), founded in 1919, which regulates the inspection of pressure vessels in the USA, has a four-leaf cloverleaf ( stylized cloverleaf ) in its logo.
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