Marijuana, Herb, Ganja, Sensi, Sinsemilla, Hemp, Weed, Jonko, Indica, Sativa, Ruderalis, Autoflower or just cannabis. Despite the different names it's all about one and the same plant: the Cannabis plant. Throughout the years different names have been given to cannabis by various countries/cultures. Also different names have been conceived for the classification of cannabis because there is a big variation of it in practice.
Indica, Sativa (and Ruderalis) generally refers to the (subspecies) of cannabis, which is native to certain parts of the world. The subspecies are the result of a cannabis plant feature to adapt itself to the environment. Hemp falls under the subspecies Cannabis Sativa category, and this is mainly used for industrial purposes.
Cannabis Sativa L. is the scientific name that was first published in 1753 by the botanist Carl Linnaeus. The scientific name Cannabis Indica was given in 1785 by Jean-Baptiste Lamark to cannabis, which he saw growing in India. In practice, there are a range of differences between cannabis, hence the names Sativa and Indica as a way to categorize various types of cannabis: Cannabis Taxonomy. In those categories various growth patterns (shape of the leaves, space between internodes), specific plant characteristics (growth and flowering time) and finally the flavors/effects (various cannabinoids and terpenes) can be distinguished. The info graphic below shows the most important differences between Sativas and Indicas.
When different types of cannabis are crossed with each other hybrids are created. Hybrids (Cannabis Hybrids) always contain a certain ratio of Indica and Sativa; Sativa-dominant (Sativa > Indica) or Indica-dominant (Indica > Sativa). When a hybrid is also crossed with Ruderalis cannabis then this hybrid becomes a kind of Autoflower. Autoflowers are therefore always a mix of Indica and/or Sativa and Ruderalis.
Indicas are short, compact, wide cannabis plants that require less space than Sativas. An Indica can be mainly recognized by its color and the characteristics of the leaf, they are dark green and wide (broad-leaves). The color is due to large amounts of chlorophyll in the leaves, and its purpose is to make light useful for the photosynthesis process. It can be said that the more chlorophyll is present in the leaf the less light is required for the growth/progression of the plant. So an Indica requires relatively less light to thrive, this corresponds with the origin of the Indica plant (they do not appear around the equator; the farther you get from the equator the lower the sunlight intensity becomes).
Indicas originate from Central Asia and the Indian subcontinent: Pakistan, Northern India, Tibet, Nepal, Afghanistan etc. The inter-nodes of an Indica are short and closer together so that the plant appears very 'bushy'. Also its flowers (buds) are very compact. If an Indica starts to flower, or the flowering process is activated (12/12 light schedule), then the height of the plant will increase by 50% up to 100%. The flowering period of an Indica is about 6 to 9 weeks. This means that an Indica is ready to be harvested more quickly than a Sativa. A revised taxonomy developed by Robert Connell Clarke, categorizes the Indica as the Broad-Leaf Drug variety (BLD) - read more about this taxonomic classification in Cannabis: Ethnobotany & Evolution.
Sativas are long, thin, high cannabis plants and can become very large (larger than Indicas under the same conditions). Sativas can be recognized by their bright colored leaves (this is because there is less chlorophyll present than Indicas), and by their narrow leaves. So Sativas need relatively more light to thrive than Indicas, this also has to do with their origin (they grow in areas near the equator, higher light intensity of the sun).
Types of Sativas can be found in: Jamaica, Southern India, Thailand, Mexico, Columbia, Africa etc. The inter-nodes of a Sativa are further apart, which is why a Sativa is often described as 'stretchy'. Sativas fly to the heights, especially when they are put into flowering. When flowering, the height of a Sativa increases by 200% to 300%. This means that Sativas are not suitable for commercial growing operations with limited space. The flowering period of Sativas is about 9 to 15 weeks, so it can take twice as long than the flowering period of Indicas (another reason why Sativas are not very suitable for commercial growing operations). According to 'Robert Connell Clarke taxonomy' Sativas can be categorized as the Narrow-leaf variety Drug (NLD) - read more about this taxonomic classification in Cannabis: Ethnobotany & Evolution.
Source: Cannabis Ethnobotany & Evolution
Ruderalis is a short, sturdy, wild type of cannabis with fewer leaves and low concentrations of THC. Ruderalis originates in tundra areas, where the summers are very short, which is why this kind has adapted itself to flower in a short period of sunlight. Ruderalis is not suitable for consumption but is often crossed with Indicas and Sativas to make Autoflower hybrids. Autoflowers begin to produce flowers (buds) depending on their age unlike Indicas and Sativas where the flowering process is dependent on light cycles.