Introduction

Depending on the taxonomical treatment adopted,¹ the genus Cannabis (Hemp, Family Cannabaceae) includes up to three species, each with a very long history of domestication. Plants belonging to this genus are probably indigenous to the Asiatic Continent, where they preferably grew in wet places and near water bodies.² This kind of environment was also frequently chosen as a temporary settlement by human nomadic groups, before the discovery and diffusion of agricultural techniques.³ Cannabis species in the wild had a weedy attitude, growing in soils with high concentrations of nitrogen released by animal dejections and human activities.² The long coexistence between mankind and hemp led to an early domestication of the plant, which soon showed an amazing spectrum of possible utilizations. Hemp has been used as a source of textiles, as an edible plant,⁴ and as a medicinal and psychoactive plant⁵ (resins produced by secretory glandular trichomes). In recent times, hemp fibers have been used to produce bioplastic and antibacterial agents; moreover, the trichomes are considered as biofactories of phytochemicals with multiple biotechnological applications.⁶ The extent of Cannabis domestication has been so persistent to cause the disappearing of the wild species: nowadays, the specie(s) belonging to the genus Cannabis are represented by myriads of cultivated varieties, which occasionally escape cultivation and grow also in the wild, giving life to forms that lose some features typical of cultivated ones. For this reason, the nomenclature of Cannabis has unstable foundations and has been the object of numerous taxonomic treatments. To fully understand the difficulties in applying a shared nomenclature to Cannabis, a digression is necessary to describe what is a species (Table 1) and what means to give a name to a species.

An Outline of Nomenclatural Rules in Botany

Naturals sciences rely on shared nomenclatural rules. Although this statement sounds obvious now, it was not so for centuries, until at the beginning of the 18th Century became evident that there was a need to develop efficient nomenclatural tools for handling an increasing number of organisms. Naturalists during the 16th and 17th Centuries applied to species names that were actually short descriptions (polynomial system). The tendency toward a simplification of nomenclature was already evident in the Pinax Theatri Botanici, written in 1623 by Caspar Bauhin,⁷ but only in the mid of 18th century Carl von Linnaeus provided a new framework to nomenclature, recommending in his Species Plantarum⁸ that each species should be designated by a nomen trivialis, formed by the union of the generic name with a single word (epithet). By the second half of 18th century, this binomial nomenclature was adopted worldwide, and the need for a set of nomenclatural rules was already raised by JB Lamarck at the end of the same Century.⁹ The first formalized laws for the nomenclature of plant species were prepared by Alphonse De Candolle in 1867,¹⁰ but only in the 20th century both botanists and zoologists produced Codes of nomenclature, accepted by the international community of scholars. As far as botany is concerned, the International Code of Botanical Nomenclature has set up the rules for naming plants starting from the International Botany Congress held in Vienna in 1905.¹¹ However, the first Code accepted by the botanist community is the Cambridge International Code¹² and only after the Second World War a regular update of the Code has been carried out every 6 years. Since its last edition,¹³ the Code has been renamed as the International Code of Nomenclature for Algae, Fungi, and Plants (ICN). The system proposed by the ICN is closed and hierarchically arranged (Table 2).

A taxonomic group of any rank (generically called taxon) can be considered as valid if: (1) it has been regularly published; (2) it has not been diversely and correctly named before (priority); and (3) it has been typified. A type is a material on which the description of a taxon is based. In the case of a plant species, it is generally a herbal specimen. The specimen on which the description is based is called the holotype (Table 3).

All nomenclatural rules included in the Code are based on the taxon system, and this architecture raises some important questions. The hierarchical system of taxa, although the Code is scientifically neutral and provides only a series of conventional rules, is deeply rooted into evolutionary theory. Most practitioners in nomenclature consider a taxon as a monophyletic entity¹⁴ and arrange the nomenclature according to the current opinions on plant phylogeny. This tendency is particularly evident when new taxa are created or separated following molecular approaches, for example, DNA barcoding.¹⁵What is the position of cultivated plants like Cannabis in this framework? It is acknowledged that the botanical entities known as cultivated varieties are a product of human selection and cannot be assimilated to wild varietates. In contrast to these latter, cultivated varieties (cultivars) are a product of human activity and are not subjected to the selective pressure of the environment.¹⁶ This argument has been largely debated, and the idea that cultivars should be considered as a separate matter is not new. Linnaeus was the first to place cultivated plants under a separated category, suggesting the adoption of different nomenclatural rules for them.¹⁷ However, it was not until 1953 that the first edition of the International Code of Nomenclature for Cultivated Plants (ICNCP) was published.¹⁸

The first and foremost principle of the ICNCP is that the names of cultivated plants cannot be handled using the system of taxon, which is replaced by the culton (a systematic group of cultivated plants).¹⁹ The core entity of the nomenclatural system for cultivated plants is the cultivated variety or cultivar (Table 4). Each cultivar is the product of human selection and is directed toward definite goals related to human activities. The cultivar can be reproduced and is not subjected to extinction. The nomenclatural system of cultivars is open: each name of a cultivar is not exclusive and the same cultivar could have different names, depending on the scope of the classification.¹⁶ Cultivars are static units; they are defined by a set of characters and are linked to a standard, generally a specimen, or a document.¹⁹

The Classification of Cannabis

The existence of cultivated and wild entities of hemp dates back to Dioscorides and passing from the physicians and botanists of the Renaissance (the German botanist Leonardt Fuchs was the first to adopt the term sativa, for indicating the domesticated hemp²⁰) survived until the 18th Century, when Linnaeus in Species Plantarum⁸described a single species of hemp, Cannabis sativa. Later, Jean-Baptiste Lamarck⁹proposed two species of Cannabis: C. sativa, the species largely cultivated in the western continents, and Cannabis indica, a wild species growing in India.²¹ The taxonomic treatment of Lamarck was rejected about 50 years later by J. Lindley,²² who restricted Cannabis to C. sativa, following Linnaeus’ classification, and the concept of Cannabis as a monospecific genus was confirmed in the following century. Only in the second decade of 1900’s a new species, Cannabis ruderalis,²³ was erected, whereas the reinstatement of the species C. indica was more recently suggested by Schultes et al.²⁴In more recent times, genomic DNA studies to classify C. sativa have been carried out using Cannabis varieties of different geographical origin. The results seem to suggest that a polytypic concept of Cannabis cannot be ruled out.²⁵ In addition, chemotaxonomical markers are a promising tool to identify different Cannabisaccessions and to screen hybrids, taking into account that all Cannabis varieties intercross successfully and produce fertile hybrids.²⁶

A biphasic approach, combining morphological and chemical characters (fruit morphology and Δ⁹-tetrahydrocannabinol [THC] content) was adopted by Small and Cronquist,¹ who recognized the following four Cannabis taxa (all belonging to the single species C. sativa) that “coexist dynamically by means of natural and artificial selection”:

• 1. Cannabis sativa L. subsp. sativa var. sativa;

• 2. Cannabis sativa L. subsp. sativa var. spontanea Vavilov;

• 3. Cannabis sativa L. subsp. indica Small & Cronquist var. indica (Lam) Wehmer;

• 4. Cannabis sativa L. subsp. indica Small & Cronquist var. kafiristanica(Vavilov) Small & Cronquist.

According to the authors, both varietates belonging to the subspecies sativa are common in North America, Europe, and Asia and show a limited intoxicant potential. In contrast, the varietates of the subspecies indica have high intoxicant potential and grow mainly in the Asiatic Continent.

Recently, Small² has proposed two possible classification of Cannabis, one based on ICP, which confirms his previous taxonomical treatment, and a new classification system for domesticated Cannabis, which is based on ICNCP and recognizes six groups of cultivars as follows:

• 1. Group of the non-narcotic plants, domesticated for stem fiber and/or oil seed in Western Asia and Europe. Low THC and high cannabidiol (CBD);

• 2. Group of the non-narcotic plants domesticated in East Asia, mainly China. Low to moderate THC, high CBD;

• 3. Group of the narcotic plants domesticated in South Central Asia. High cannabinoids, mostly THC;

• 4. Group of the narcotic plants domesticated in South Asia (Afghanistan and neighboring Countries), contains both THC and CBD.

In addition, there are also at least two stabilized hybrid groups with intermediate characters between the four groups (Table 5).

This recent systematic treatment calls attention to the still existing practical difficulties of applying the International Code of Nomenclature to the genus Cannabis. Small² is careful in the application of the code, and this cautious attitude is the consequence of the perplexity about considering Cannabis exclusively as a cultivated plant. The studies of last two decades suggest that Cannabis, as other crops, exists in the so called crop–weed complexes, which are formed by cultivated forms and weedy forms escaped from cultivations and growing in the wild. These latter can establish new characters and are newly under the pressures of natural selection. Thus, it seems difficult to circumscribe Cannabis solely as a cultivated plant. In our opinion, an application of the taxon system to the genus Cannabis together with the sativa/indica distinction should be avoided, as recently suggested.²⁸ Due to the prevalent economic interest of the cultivated varieties of Cannabis, a simplified nomenclature system based on ICNCP should be applied. According to ICNCP, it is not mandatory to use the species epithets, sativa or indica, and a combination of the genus name and a cultivar epithet, in any language and bounded by single quotation marks (i.e., Cannabis ‘fibranova’, to cite a cultivar largely cultivated for fiber production), defines an exclusive name for each Cannabis cultivar.

However, due to its numerous medical and recreational usages, hundreds of Cannabiscultivated varieties have been developed and named with vernacular names by medical patients and recreational users. Few of these can be treated as real Cannabis cultivars, having been regularly named and registered according to the ICNCP, but many others, particularly marijuana strains, lack an adequate description and a standard. For this reason, their names cannot be accepted as cultivar epithets. Any strain that has not been formally described as a cultivar, for example, the so called Sour diesel, or Granddaddy Purple, should be named as follows: Cannabis strain Sour diesel, or strain Granddaddy Purple, with their popularized name without single quotation marks, having in mind that their names have no taxonomical validity.

Abbreviations Used

References

References