Information:  - Diatoms are a major group of algae, and are among the most common types of phytoplankton. Diatoms are unicellular, although they can form colonies in the shape of filaments or ribbons (e.g. "Fragilaria"), fans (e.g. "Meridion"), zigzags (e.g. "Tabellaria"), or stars (e.g. "Asterionella"). The first diatom formally described in scientific literature, the colonial "Bacillaria paradoxa", was found in 1783 by Danish naturalist Otto Friedrich Müller. Diatoms are producers within the food chain. A unique feature of diatom cells is that they are enclosed within a cell wall made of silica (hydrated silicon dioxide) called a frustule. These frustules show a wide diversity in form, but are usually almost bilaterally symmetrical, hence the group name. The symmetry is not perfect since one of the valves is slightly larger than the other, allowing one valve to fit inside the edge of the other. Fossil evidence suggests that they originated during, or before, the early Jurassic period. Only male gametes of centric diatoms are capable of movement by means of flagella. Diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality.  - Trigonella is a genus from the family Fabaceae. The best known member is the herb fenugreek.  - Clover or trefoil are common names for plants of the genus Trifolium (Latin, "tres" "three" + "folium" "leaf"), consisting of about 300 species of plants in the leguminous pea family Fabaceae. The genus has a cosmopolitan distribution; the highest diversity is found in the temperate Northern Hemisphere, but many species also occur in South America and Africa, including at high altitudes on mountains in the tropics. They are small annual, biennial, or short-lived perennial herbaceous plants. Clover can be evergreen. The leaves are trifoliate (rarely quatrefoiled, cinquefoil, or septfoil), with stipules adnate to the leaf-stalk, and heads or dense spikes of small red, purple, white, or yellow flowers; the small, few-seeded pods are enclosed in the calyx. Other closely related genera often called clovers include "Melilotus" (sweet clover) and "Medicago" (alfalfa or Calvary clover).  - Alfalfa , Medicago sativa also called lucerne, is a perennial flowering plant in the pea family Fabaceae cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, and silage, as well as a green manure and cover crop. The name alfalfa is used in North America. The name lucerne is the more commonly used name in the United Kingdom, South Africa, Australia, and New Zealand. The plant superficially resembles clover (a cousin in the same family), especially while young, when trifoliate leaves comprising round leaflets predominate. Later in maturity, leaflets are elongated. It has clusters of small purple flowers followed by fruits spiralled in 2 to 3 turns containing 1020 seeds. Alfalfa is native to warmer temperate climates. It has been cultivated as livestock fodder since at least the era of the ancient Greeks and Romans. Alfalfa sprouts are a common ingredient in dishes made in South Indian cuisine.  - Nitrogen fixation is a process by which nitrogen in the Earth's atmosphere is converted into ammonia (NH) or other molecules available to living organisms. Atmospheric nitrogen or molecular dinitrogen (N) is relatively inert: it does not easily react with other chemicals to form new compounds. The fixation process frees nitrogen atoms from their triply bonded diatomic form, NN, to be used in other ways.  - A shrub or bush is a small to medium-sized woody plant. It is distinguished from a tree by its multiple stems and shorter height, usually under 6 m (20 ft) tall. Plants of many species may grow either into shrubs or trees, depending on their growing conditions. Small, low shrubs, generally less than 2 m (6.6 ft) tall, such as lavender, periwinkle and most small garden varieties of roses, are often termed subshrubs.  - Melilotus, known as melilot, sweet clover, and kumoniga (from the Cumans), is a genus in the family Fabaceae (the same family that also includes the "Trifolium" clovers). Members are known as common grassland plants and as weeds of cultivated ground. Originally from Europe and Asia, it is now found worldwide.  - Medicago is a genus of flowering plants, commonly known as medick or burclover, in the legume family. It contains at least 87 species and is distributed mainly around the Mediterranean basin. The best-known member of the genus is alfalfa ("M. sativa"), an important forage crop, and the genus name is based on the Latin name for that plant, "medica", from median (grass). Most members of the genus are low, creeping herbs, resembling clover, but with burs (hence the common name). However, alfalfa grows to a height of 1 meter, and tree medick ("M. arborea") is a shrub. Members of the genus are known to produce bioactive compounds such as medicarpin (a flavonoid) and medicagenic acid (a triterpenoid saponin). Chromosome numbers in "Medicago" range from 2"n" = 14 to 48.  - Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. "Rhizobium" species form an endosymbiotic nitrogen-fixing association with roots of legumes and "".  - Medicago falcata is a plant species of the genus Medicago . It is native to the Mediterranean basin , but is found throughout the world . It forms a symbiotic relationship with the bacterium Sinorhizobium meliloti , which is capable of nitrogen fixation . Its common names include blue alfalfa , sickle alfalfa , sickle medick , yellow lucerne , and yellow - flowered alfalfa .  - Triterpenoid saponins are triterpenes which belong to the group of saponin compounds. Triterpenes are a type of terpene containing 30 carbon atoms. Triterpenes are assembled from a five-carbon isoprene unit through the cytosolic mevalonate pathway to make a thirty-carbon compound. Some triterpenes are steroidal in nature. Cholesterol, phytosterols and phytoecdysteroids are triterpenes. The triterpenes are subdivided into some 20 groups, depending on their particular structures. Some triterpenoid compounds are found as saponin glycosides which refers to the attachment of various sugar molecules to the triterpene unit. These sugars can be cleaved off in the gut by bacteria, sometimes allowing the aglycone (triterpene) to be absorbed into the bloodstream or to insert into cell membranes.   - Flavonoids (or bioflavonoids) (from the Latin word "flavus" meaning yellow, their color in nature) are a class of plant and fungus secondary metabolites.  - Root nodules occur on the roots of plants (primarily Fabaceae) that associate with symbiotic nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known as rhizobia. This process has evolved multiple times within the Fabaceae, as well as in other species found within the Rosid clade. The Fabaceae include legume crops such as beans and peas.  - Sinorhizobium meliloti is a Gram-negative nitrogen-fixing bacterium (rhizobium). It forms a symbiotic relationship with legumes from the genera "Medicago", "Melilotus" and "Trigonella", including the model legume "Medicago truncatula". This symbiosis results in a new plant organ termed a root nodule. The "S. meliloti" genome contains three replicons: a chromosome (~3.7 megabases) and two chromids, pSymA (~1.4 megabases) and pSymB (~1.7 megabases). Five "S. meliloti" genomes have been sequenced to date: Rm1021, AK83, BL225C, Rm41, and SM11  - Medicago truncatula, the barrelclover, strong-spined medick, barrel medic, or barrel medick, is a small annual legume native to the Mediterranean region that is used in genomic research. It is a low-growing, clover-like plant 1060 cm tall with trifoliate leaves. Each leaflet is rounded, 12 cm long, often with a dark spot in the center. The flowers are yellow, produced singly or in a small inflorescence of two to five together; the fruit is a small, spiny pod.  - A legume (or ) is a plant or its fruit or seed in the family Fabaceae (or Leguminosae). Legumes are grown agriculturally, primarily for their grain seed called pulse, for livestock forage and silage, and as soil-enhancing green manure. Well-known legumes include alfalfa, clover, peas, beans, lentils, lupin bean, mesquite, carob, soybeans, peanuts and tamarind. "Fabaceae" is the most common family found in tropical rainforests and in dry forests in the Americas and Africa.    Given the information, choose the subject and object entities that have the relation of 'parent taxon'.
A:
medicago falcata , medicago sativa