The last section highlights the scarcity of information in regard to the Iberian Peninsula, in comparison with most European regions, evaluates the potential causes for this paucity and suggests how further research could contribute to bridging this knowledge gap. Time units used: Ma, million years before present; yr BP, years before present; CE/ BCE, Common Era/Before Common Era. Cannabis sativa is a sun-loving  species that requires well-drained and nitrogen-rich soils, warmth and moisture. Therefore, most natural populations are found seasonally across accommodating northern temperate latitudes. This plant grows well along exposed riverbanks, lakesides, margins of agricultural lands and other areas disturbed by humans. Cannabis plants are annual and usually diecious,cannabis grow tray as determined by X and Y chromosomes, and anemophylous . The annual cycle extends from spring  to summer  and autumn . Male plants, which are slightly taller than female plants, die shortly before pollination. Female plants ripen viable seeds just before the arrival of winter killing frosts. Seed dissemination is carried out mostly by wind or feeding birds.

During germination, seeds are surrounded by bracts with hairs that produce a resinous blend of cannabinoids and aromatic compounds as secondary metabolites, which are believed to protect seeds against pests and pathogens. Cannabinols may be psychoactive  or not psychoactive  for humans . Early attempts to identify the place of origin of wild Cannabis prior to human contact were based on the geographic distribution of its wild, cultivated and ruderal populations, combined with the known ecological requirements and reproductive strategies. However, the distribution of this plant and its biotypes/varieties is closely associated with human settlements and trade routes, and therefore, the original native range is obscured . In spite of this, a broad area referred to as central Asia  was proposed as the center of origin of Cannabis . Another, less generally accepted, possibility mentioned was south Asia . Regarding timing, accepting that the central Asian steppes were colonized by humans by 35,000 years ago , it has been assumed that wild Cannabis could have originated earlier. These hypotheses, however, were based on circumstantial evidence, and robust empirical evidence was lacking. This empirical evidence was provided by the fossil record and the use of time-calibrated molecular DNA phylogenies.

The macrofossil record of Cannabis is relatively scarce and consists of only a few leaf and fruit/seed impressions with ages ranging between the Oligocene and the late Miocene . However, microfossils, vertical grow systems for sale specifically pollen, are abundant and widespread and have commonly been utilized to reliably reconstruct the history of Cannabis. Nevertheless, the identification of Cannabis pollen deserves special attention because of its similarity with other members of the family Cannabaceae, especially Humulus , a sister genus that bears contrasting ecological requirements and cultural connotations. Therefore, inaccurate identification might lead to erroneous conclusions . This is why different authors have used broader taxonomic categories for this pollen type, such as Cannabis-type, Cannabis/Humulus or Cannabaceae. In addition, it is unclear whether pollen from wild and cultivated Cannabis may be distinguished morphologically.Godwin  emphasized several differential characteristics of the pore complex. Further statistical studies revealed that Cannabis pollen is generally larger than Humulus, but this character alone was not sufficient to allow reliable separation . Pollen size also seems to be an unreliable parameter to separate wild from cultivated Cannabis .

The combination of pore complexes and size seems to provide a more reliable, yet not universally accepted, identification criterion to differentiate between Cannabis and Humulus pollen . However, even in the case of conclusive Cannabis pollen identifications, comparisons with studies referring to this pollen type as Cannabis-type, Cannabis/Humulus or Cannabaceae remain problematic, which may be a handicap for the development of meta-analyses aimed at reconstructing past biogeographic and cultural patterns. Recently, some meta-analyses have been conducted using different criteria, such as considering the entire Cannabis/Humulus complex or taking into account only those studies that explicitly identified Cannabis pollen . These approaches tend to overestimate or underestimate the actual pollen record of Cannabis. A different approach, called here the assemblage approach, has recently been proposed by McPartland et al. . These authors noted that wild C. sativa is typical of open temperate steppe habitats dominated by grasses, chenopods and Artemisia, whereas Humulus is a vine plant that requires trees to climb and is common in temperate deciduous forests dominated by alder , willow  and poplar .