question: Why did various edible garden weeds not get cultivated and farmed by humans?
comment: Basically all the grain crops were "weeds" which have been bred and developed to be the useful crops they now are, they bear very little resemblance to the original plants.
passages: Section::::Dispersal.
  
  Many weed species have moved out of their natural geographic ranges and spread around the world in tandem with human migrations and commerce. Weed seeds are often collected and transported with crops after the harvesting of grains, so humans are a vector of transport as well as a producer of the disturbed environments to which weed species are well adapted, resulting in many weeds having a close association with human activities.
   Many noxious weeds have come to new regions and countries through contaminated shipments of feed and crop seeds or were intentionally introduced as ornamental plants for horticultural use.
  
  Some "noxious weeds", such as ragwort, produce copious amounts of nectar, valuable for the survival of bees and other pollinators, or other advantages like larval host foods and habitats. Wild parsnip, "Pastinaca sativa", for instance, provides large tubular stems that some bee species hibernate in, larval food for two different swallowtail butterflies, and other beneficial qualities.
  
  Section::::Types.
   Some of the species cultivated by Native Americans for food are today considered undesirable weeds. Another name for marshelder is sumpweed; chenopods are derisively called pigweed, although one South American species with a more attractive name, quinoa, is a health food store favorite. Many plants considered weeds are the colonizers of disturbed soil, the first fast-growing weeds to spring up when a natural or man-made event, such as a fire, leaves a bare patch of soil.
   Some plants become dominant when introduced into new environments because the animals in their original environment, that compete with them or feed on them are absent; in what is sometimes called the “natural enemies hypothesis”, plants freed from these specialist consumers may become dominant. An example is Klamath weed, that threatened millions of hectares of prime grain and grazing land in North America after it was accidentally introduced, but was reduced to a rare roadside weed within several years after some of its natural enemies were imported during World War II. In locations where predation and mutually competitive relationships are absent, weeds have increased resources available for growth and reproduction. The weediness of some species that are introduced into new environments may be caused by their production of allelopathic chemicals which indigenous plants are not yet adapted to, a scenario sometimes called the "novel weapons hypothesis". These chemicals may limit the growth of established plants or the germination and growth of seeds and seedlings.
   Examples of such ruderal or pioneer species include plants that are adapted to naturally occurring disturbed environments such as dunes and other windswept areas with shifting soils, alluvial flood plains, river banks and deltas, and areas that are burned repeatedly. Since human agricultural practices often mimic these natural environments where weedy species have evolved, some weeds are effectively preadapted to grow and proliferate in human-disturbed areas such as agricultural fields, lawns, roadsides, and construction sites. The weedy nature of these species often gives them an advantage over more desirable crop species because they often grow quickly and reproduce quickly, they commonly have seeds that persist in the soil seed bank for many years, or they may have short lifespans with multiple generations in the same growing season. In contrast, perennial weeds often have underground stems that spread under the soil surface or, like ground ivy ("Glechoma hederacea"), have creeping stems that root and spread out over the ground.
   In 2016, 29% of wild relative plant species were completely missing from the world’s genebanks, with a further 24% represented by fewer than 10 samples. Over 70% of all crop wild relative species worldwide were in urgent need of further collecting to improve their representation in genebanks, and over 95% were insufficiently represented with regard to the full range of geographic and ecological variation in their native distributions. While the most critical priorities for further collecting were found in the Mediterranean and Near East, Western and Southern Europe, Southeast and East Asia, and South America, crop wild relatives insufficiently represented in genebanks are distributed across almost all countries worldwide.
   Weeds are unwanted plants growing in managed environments such as farms, urban areas, gardens, lawns, and parks. People have spread plants beyond their native ranges and some of these introduced plants become invasive, damaging existing ecosystems by displacing native species, and sometimes becoming serious weeds of cultivation.
   It has long been assumed that weeds, in the sense of rapidly evolving plants taking advantage of human-disturbed environments, evolved in response to the Neolithic agricultural revolution approximately 12,000 years ago. However, researchers have found evidence of "proto-weeds" behaving in similar ways at Ohalo II, a 23,000-year-old archeological site in Israel.
  
  Section::::See also.
  
  BULLET::::- Crop weeds
  
  BULLET::::- Introduced species
  
  BULLET::::- Invasive species
  
  BULLET::::- List of beneficial weeds
  
  BULLET::::- Pest (organism)
  
  BULLET::::- Superweeds
  
  BULLET::::- Vavilovian mimicry
  
  BULLET::::- Vermin
  
  BULLET::::- Volunteer (botany)
  
  BULLET::::- Weed of cultivation
  
  Section::::External links.
  
  BULLET::::- IUCN Invasive Species Specialist Group
   Flower evolution continues to the present day; modern flowers have been so profoundly influenced by humans that some of them cannot be pollinated in nature. Many modern domesticated flower species were formerly simple weeds, which sprouted only when the ground was disturbed. Some of them tended to grow with human crops, perhaps already having symbiotic companion plant relationships with them, and the prettiest did not get plucked because of their beauty, developing a dependence upon and special adaptation to human affection.
   Peaches, for example, originated in China, and have been carried to much of the populated world. Tomatoes are native to the Andes. Squash (pumpkins), maize (corn), and tobacco are native to the Americas, but were introduced to the Old World. Many introduced species require continued human intervention to survive in the new environment. Others may become feral, but do not seriously compete with natives, but simply increase the biodiversity of the area.
  
  Dandelions are also introduced species to North America.
   Weeds have existed since the advent of settled agriculture around 10,000 years ago it is been suggested that the most common characteristic of the ancestors of our presently dominant crop plants is their willingness—their tendency to be successful, to thrive, in disturbed habitats, mostly those around human dwellings. Farmers have likely always been aware of weeds in their crops, although the evidence for their awareness and concern is nearly all anecdotal. 
  
  Unlike other agricultural sciences like entomology or plant pathology, the emergence of weed science is comparatively recent largely within the 20th century. 
   Weeds have long been a concern, perhaps as long as humans have cultivated plants. They are mentioned in various historic texts, such as a Shakespearean sonnet:
  
  To thy fair flower add the rank smell of weeds: / But why thy odour matcheth not thy show, / The soil is this, that thou dost common grow.
  
  and the Bible:
   Crop diversity is an aspect of biodiversity important for food security. The loss of biodiversity is considered one of today’s most serious environmental concerns by the Food and Agriculture Organization. If current trends persist, as many as half of all plant species could face extinction. Among the many threatened species are wild relatives of our crops – the wild and weedy cousins of domesticated plants that possess valuable traits for crop breeding, such as pest and disease resistance. Some 6% of wild relatives of cereal crops such as wheat, maize, rice, and sorghum are under threat, as are 18% of legumes (Fabaceae), the wild relatives of beans, peas and lentils, and 13% of species within the botanical family (Solanaceae) that includes potato, tomato, eggplant (aubergine), and peppers ("Capsicum"). In 2016, 29% of wild relative plant species were completely missing from the world’s genebanks, with a further 24% represented by fewer than 10 samples. Over 70% of all crop wild relative species worldwide were in urgent need of further collecting to improve their representation in genebanks, and over 95% were insufficiently represented with regard to the full range of geographic and ecological variation in their native distributions. While the most critical priorities for further collecting were found in the Mediterranean and Near East, Western and Southern Europe, Southeast and East Asia, and South America, crop wild relatives insufficiently represented in genebanks are distributed across almost all countries worldwide.
   Crops refer to groups of plants grown for consumption. Despite domestication over many years, these plants are not so far removed from their wild relatives that they could reproduce if brought together. Many crops are still grown in the areas they originated and gene flow between crops and wild relatives impacts the evolution of wild populations. Farmers can avoid reproduction between the different populations by timing their planting of crops so that crops are not flowering when wild relatives would be. Domesticated crops have been changed through artificial selection and genetic engineering. The genetic make up of many crops is different than that of its wild relatives, but the closer they grow to one another the more likely they are to share genes through pollen. Gene flow persists between crops and wild counterparts.
   The process of domestication of wild plants cannot be described with any precision. However, Bruce D. Smith and other scholars have pointed out that three of the domesticates (chenopods, "I. annua", and "C. pepo") were plants that thrived in disturbed soils in river valleys. In the aftermath of a flood, in which most of the old vegetation is killed by the high waters and bare patches of new, often very fertile, soil were created, these pioneer plants sprang up like magic, often growing in almost pure stands, but usually disappearing after a single season, as other vegetation pushed them out until the next flood.
   The archaeological record suggests that humans were collecting these plants from the wild by 6000 BC. In the 1970s, archaeologists noticed differences between seeds found in the remains of pre-Columbus era Native American hearths and houses and those growing in the wild. In a domestic setting, the seeds of some plants were much larger than in the wild, and the seeds were easier to extract from the shells or husks. This was evidence that Indigenous gardeners were selectively breeding the plants to make them more productive and accessible.
   Other examples are "Centaurea solstitialis" (yellow starthistle) and "Centaurea diffusa" (diffuse knapweed). These Eastern European noxious weeds have spread through the western and West Coast states. Experiments show that 8-hydroxyquinoline, a chemical produced at the root of "C. diffusa", has a negative effect only on plants that have not co-evolved with it. Such co-evolved native plants have also evolved defenses. "C. diffusa" and "C. solstitialis" do not appear in their native habitats to be overwhelmingly successful competitors. Success or lack of success in one habitat does not necessarily imply success in others. Conversely, examining habitats in which a species is less successful can reveal novel weapons to defeat invasiveness.
   Many other species have become naturalized outside the Americas after having been introduced by people, especially in Australia, Hawaii, and the Mediterranean region. In Australia, species of "Opuntia", particularly "Opuntia stricta", were introduced in the 19th century for use as natural agricultural fences and in an attempt to establish a cochineal industry. They rapidly became a major weed problem, but are now controlled by biological agents, particularly the moth "Cactoblastis cactorum". The weed potential of Opuntia species in Australia continues however, leading to all opuntioid cacti except "O. ficus-indica" being declared Weeds of National Significance by the Australian Weeds Committee in April 2012.
   Wild ancestors in plants are direct origin of certain plants. Thousands of years ago, humans started to settle and grow crops. This change in human behaviour from nomadic to sedentary marked the start of the domestication process of plants. Creating high-yielding and adaptable plant varieties. A lot of crop plants were also moved into human-managed conditions which caused the selection pressures to differ from the plants in its normal environment creating a significant difference in trait, life cycle and appearances compared to its original predecessor. 
   In 1923, Clark and Fletcher suggested that the "annual losses due to the occurrence of pernicious weeds on farm land in Canada, although acknowledged in a general way, are far greater than is realized." They thought this was because "farmers gave little critical attention to the weeds growing among their crops." They did not deny that farmers were aware of the weeds only that they could do little about them. Many of the same weeds described by Clark and Fletcher are shown in most current weed identification books. In spite of continued research to mitigate weeds annually many of the same species continue to be problematic. 
   The conventional approach was probably the first to be employed, since it is comparatively easy to destroy weeds by burning them or ploughing them under, and to kill larger competing herbivores. Techniques such as crop rotation, companion planting (also known as intercropping or mixed cropping), and the selective breeding of pest-resistant cultivars have a long history.
   Some of the most striking and valuable results have been achieved by introducing as progenitors, certain weeds belonging to the same natural order of plants as the cultivated parents. For example, an inferior variety of "spelt" wheat Triticum spelta from Southern Asia, has been employed with excellent results to introduce strength of gluten to the grain, and large yielding and standing power to the crop with immunity from shedding its seed during harvest.
   Some weed species have been classified as noxious weeds by government authorities because, if left unchecked, they often compete with native or crop plants or cause harm to livestock. They are often foreign species accidentally or imprudently imported into a region where there are few natural controls to limit their population and spread.
  
  Section::::Weeds as adaptable species.
   Similar "C. ruderalis" populations can be found in most of the areas where hemp cultivation was once prevalent. The most notable region in North America is the midwestern United States, though populations occur sporadically throughout the United States and Canada. Large wild "C. ruderalis" populations are also found in central and eastern Europe, most of them in Ukraine, Lithuania, Belarus, Latvia, Estonia and adjacent countries. Without human selection, these plants have lost many of the traits they were originally selected for, and have acclimated to their environment.
  
  Section::::Cultivation.
   Weeds can also host pests and diseases that can spread to cultivated crops. Charlock and Shepherd's purse may carry clubroot, eelworm can be harboured by chickweed, fat hen and shepherd's purse, while the cucumber mosaic virus, which can devastate the cucurbit family, is carried by a range of different weeds including chickweed and groundsel.
  
  Insect pests often do not attack weeds. However pests such as cutworms may first attack weeds then move on to cultivated crops.
  
presuppositions: Garden weeds were not cultivated by humans. Various edible garden weeds were never cultivated and farmed by humans.
corrections: Garden weeds were farmed and developed into modern grain crops. Grain crops were originally considered weeds but they then were bred and developed to become useful crops.
raw_presuppositions: Garden weeds were not cultivated by humans. Various edible garden weeds were never cultivated and farmed by humans.
raw_corrections: Garden weeds were farmed and developed into modern grain crops. Grain crops were originally considered weeds but they then were bred and developed to become useful crops.