Marijuana Botany

by Robert Connell Clarke

Floral Traits

Many individual traits determine the floral characteristics of Cannabis This section will focus on the individual traits of pistillate floral clusters with occasional comments about similar traits in staminate floral clusters. Pistillate flowering clusters are the seed-producing organs of Cannabis; they remain on the plant and go through many changes that cannot be compared to staminate plants.

Shape

The basic shape of a floral cluster is determined by the internode lengths along the main floral axis and within individual floral clusters. Dense, long clusters result when internodes are short along a long floral axis and there are short internodes within the individual compact floral clusters (Hindu Kush). Airy clusters result when a plant forms a stretched floral axis with long internodes between well-branched individual floral clusters (Thailand).

The shape of a floral cluster is also determined by the general growth habit of the plant. Among domestic Cannabis phenotypes, for instance, it is obvious that floral clusters from a creeper phenotype plant will curve upwards at the end, and floral clusters from the huge upright phenotype will have long, straight floral clusters of various shapes. Early in the winter, many strains begin to stretch and cease calyx production in preparation for rejuvenation and subsequent vegetative growth in the spring. Staminate plants also exhibit variation in floral clusters. Some plants have tight clusters of staminate calyxes resembling inverted grapes (Hindu Kush) and others have long, hanging groups of flowers on long, exposed, leafless branches (Thailand).

Form

The form of a floral cluster is determined by the numbers and relative proportions of calyxes and flowers. A leafy floral cluster might be 70% leaves and have a calyx-to-leaf ratio of 1-to-4. It is obvious that strains with a high calyx-to-leaf ratio are more adapted to calyx production, and therefore, to resin production. This factor could be advantageous in characterizing plants as future parents of bud strains. At this point it must be noted that pistillate floral clusters are made up of a number of distinct parts. They include stems, occasional seeds, calyxes, inner leaves subtending calyx pairs (small, resinous, 1-3 leaflets), and outer leaves subtending entire floral clusters (larger, little resin, 3-11 leaflets). The ratios (by dry weight) of these various portions vary by strain, degree of pollination, and maturity of the floral clusters. Maturation is a reaction to environmental change, and the degree of maturity reached is subject to climatic limits as well as breeder’s preference. Because of this interplay between environment and genetics in the control of floral form it is often difficult to breed Cannabis for floral characteristics. A thorough knowledge of the way a strain matures is important in separating possible inherited traits of floral clusters from acquired traits. Chapter IV, Maturation and Harvesting of Cannabis, delves into the secrets and theories of maturation. For now, we will assume that the following traits are described from fully mature floral clusters (peak floral stage) before any decline.

Calyx Size

Mature calyxes range in size from 2 to 12 millimeters (1/16 to 3/8 inch) in length. Calyx size is largely dependent upon age and maturity. Calyx size of a floral cluster is best expressed as the average length of the mature viable calyxes. Calyxes are still considered viable if both pistils appear fresh and have not begun to curl or change colors. At this time, the calyx is relatively straight and has not begun to swell with resin and change shape as it will when the pistils die. It is generally agreed that the production of large calyxes is often as important in determining the psychoactivity of a strain as the quantity of calyxes produced. Hindu Kush, Thai, and Mexican strains are some of the most psychoactive strains, and they are often characterized by large calyxes and seeds. Calyx size appears to be an inherited trait in Cannabis. Completely acclimatized hybrid strains usually have many rather small calyxes, while imported strains with large calyxes retain that size when inbred. Initial selection of large seeds increases the chance that offspring will be of the large-calyx variety. Aberrant calyx development occasionally results in double or fused calyxes, both of which may set seed. This phenomenon is most pronounced in strains from Thailand and India.

Color

The perception and interpretation of color in Cannabis floral clusters is heavily influenced by the imagination of the cultivator or breeder. A gold strain does not appear metallic any more than a red strain resembles a fire engine. Cannabis floral clusters are basically green, but changes may take place later in the season which alter the color to include various shades. The intense green of chlorophyll usually masks the color of accessory pigments, Chlorophyll tends to break down late in the season and anthocyanin pigments also contained in the tissues are unmasked and allowed to show through. Purple, resulting from anthocyanin accumulation, is the most common color in living Cannabis, other than green. This color modification is usually triggered by seasonal change, much as the leaves of many deciduous trees change color in the fall. This does not mean, however, that expression of color is controlled by environment alone and is not an inheritable trait. For purple color to develop upon maturation, a strain must have the genetically controlled metabolic potential to produce anthocyanin pigments coupled with a responsiveness to environmental change such that anthocyanin pigments are unmasked and become visible. This also means that a strain could have the genes for expression of purple color but the color might never be expressed if the environmental conditions did not trigger anthocyanin pigmentation or chlorophyll breakdown. Colombian and Hindu Kush strains often develop purple coloration year after year when subjected to low night temperatures during maturation. Color changes will be discussed in more detail in Chapter IV Maturation and Harvesting of Cannabis.

Carotenoid pigments are largely responsible for the yellow, orange, red, and brown colors of Cannabis. They also begin to show in the leaves and calyxes of certain strains as the masking green chlorophyll color fades upon maturation. Gold strains are those which tend to reveal underlying yellow and orange pigments as they mature. Red strains are usually closer to reddish brown in color, although certain carotenoid and anthocyanin pigments are nearly red and localized streaks of these colors occasionally appear in the petioles of very old floral clusters. Red color in pressed, imported tops is often a result of masses of reddish brown dried pistils.

Several different portions of floral cluster anatomy may change colors, and it is possible that different genes may control the coloring of these various parts.

The petioles, adaxial (top) surfaces, and abaxial (bottom) surfaces of leaves, as well as the stems, calyxes, and pistils color differently in various strains. Since most of the outer leaves are removed during manicuring, the color expressed by the calyxes and inner leaves during the late flowering stages will be all that remains in the final product. This is why strains are only considered to be truly purple or gold if the calyxes maintain those colors when dried. Anthocyanin accumulation in the stems is sometimes considered a sign of phosphorus deficiency but in most situations results from unharmful excesses of phosphorus or it is a genetic trait. Also, cold temperatures might interfere with phosphorus uptake resulting in a deficiency. Pistils in Hindu Kush strains are quite often magenta or pink in color when they first appear. They are viable at this time and turn reddish brown when they wither, as in most strains. Purple coloration usually indicates that pistillate plants are over-mature and cannabinoid biosynthesis is slowing down during cold autumn weather.

Cannabinoid Level

Breeding Cannabis for cannabinoid level has been accomplished by both licensed legitimate and clandestine researchers. Warmke (1942) and Warmke and Davidson (1943-44) showed that they could significantly raise or lower the cannabinoid level by selective breeding. Small (1975a) has divided genus Cannabis into four distinct chemotypes based on the relative amounts of THC and CBD. Recent research has shown that crosses between high THC: low CBD strains and low THC: high CBD strains yield offspring of cannabinoid content intermediate between the two parents. Beutler and der Marderosian (1978) analyzed the F1 offspring of the controlled cross C. Sativa (Mexico-high THC) X C. ruderalis (Russia-low THC) and found that they fell into two groups intermediate between the parents in THC level. This indicates that THC production is most likely controlled by more than one gene. Also the F1 hybrids of lower THC (resembling the staminate parent) were twice as frequent as the higher THC hybrids (resembling the pistillate parent). More re search is needed to learn if THC production in Cannabis is associated with the sexual type of the high THC parent or if high THC characteristics are recessive. According to Small (1979) the cannabinoid ratios of strains grown in northern climates are a reflection of the cannabinoid ratio of the pure, imported, parental strain. This indicates that cannabinoid phenotype is genetically controlled, and the levels of the total cannabinoids are determined by environment. Complex highs produced by various strains of Cannabis may be blended by careful breeding to produce hybrids of varying psychoactivity, but the level of total psychoactivity is dependent on environment. This is also the telltale indication that unconscious breeding with un desirable low-THC parents could rapidly lead to the degeneration rather than improvement of a bud strain. It is ob vious that individuals of fiber strains are of little if any use in breeding bud strains.

Breeding for cannabinoid content and the eventual characterization of varying highs produced by Cannabis is totally subjective guesswork without the aid of modern analysis techniques. A chromatographic analysis system would allow the selection of specific cannabinoid types, especially staminate pollen parents. Selection of staminate parents always presents a problem when breeding for cannabinoid content. Staminate plants usually express the same ratios of cannabinoids as their pistiliate counterparts but in much lower quantities, and they are rarely allowed to reach full maturity for fear of seeding the pistillate portion of the crop. A simple bioassay for THC content of staminate plants is performed by leaving a series of from three to five numbered bags of leaves and tops of various prospective pollen parents along with some rolling papers in several locations frequented by a steady repeating crowd of marijuana smokers. The bag completely consumed first can be considered the most desirable to smoke and possibly the most psychoactive. It would be impossible for one per son to objectively select the most psychoactive staminate plant since variation in the cannabinoid profile is subtle. The bioassay reported here is in effect an unstructured panel evaluation which averages the opinions of unbiased testers who are exposed to only a few choices at a time. Such bioassay results can enter into selecting the staminate parent.

It is difficult to say how many genes might control THC-acid synthesis. Genetic control of the biosynthetic pathway could occur at many points through the action of enzymes controlling each individual reaction. It is generally accepted that bud strains have an enzyme system which quickly converts CBD-acid to THC-acid, favoring THC-acid accumulation. Fiber strains lack this enzyme activity, so CBD-acid accumulalion is favored since there is little conversion to THC-acid. These same enzyme systems are probably also sensitive to changes in heat and light.

It is supposed that variations in the type of high associated with different strains of Cannabis result from varying levels of cannabinoids. THC is the primary psycho active ingredient which is acted upon synergistically by small amounts of CBN, CBD, and other accessory cannabinoids. Terpenes and other aromatic constituents of Cannabis might also potentiate or suppress the effect of THC. We know that cannabinoid levels may be used to establish cannabinoid phenotypes and that these phenotypes are passed on from parent to offspring. Therefore, cannabinoid levels are in part determined by genes. To accurately characterize highs from various individuals and establish criteria for breeding strains with particular cannabinoid contents, an accurate and easy method is needed for measuring cannabinoid levels in prospective parents. Inheritance and expression of cannabinoid chemotype is certainly complex.

Taste and Aroma

Taste and aroma are closely linked. As our senses for differentiating taste and aroma are connected, so are the sources of taste and aroma in Cannabis. Aroma is produced primarily by aromatic terpenes produced as components of the resin secreted by glandular trichomes on the surface of the calyxes and subtending leaflets. When a floral cluster is squeezed, the resinous heads of glandular trichomes rupture and the aromatic terpenes are exposed to the air. There is often a large difference between the aroma of fresh and dry floral clusters This is explained by the polymerization (joining together in a chain) of many of the smaller molecules of aromatic ter penes to form different aromatic and nonaromatic terpene polymers. This happens as Cannabis resins age and mature, both while the plant is growing and while curing after harvest. Additional aromas may interfere with the primary terpenoid components, such as ammonia gas and other gaseous products given off by the curing, fermentation or spoilage of the tissue (non-resin) portion of the floral clusters.

A combination of at least twenty aromatic terpenes (103 are known to occur in Cannabis) and other aromatic compounds control the aroma of each plant. The production of each aromatic compound may be influenced by many genes; therefore, it is a complex matter to breed Cannabis for aroma. Breeders of perfume roses often are amazed at the complexity of the genetic control of aroma,Each strain, however, has several characteristic aromas, and these are occasionally transmitted to hybrid offspring such that they resemble one or both parents in aroma. Manytimes breeders complain that their strain has lost the desired aromatic characteristics of the parental strains. Fixed hybrid strains will develop a characteristic aroma that is hereditary and often true-breeding. The cultivator with preservation of a particular aroma as a goal can clone the individual with a desired aroma in addition to breeding it. This is good insurance in case the aroma is lost in the off spring by segregation and recombination of genes.

The aromas of fresh or dried clusters are sampled and compared in such a way that they are separated to avoid confusion. Each sample is placed in the corner of a twice folded, labeled piece of unscented writing paper at room temperature (above 650). A light squeeze will release the aromatic principles contained within the resin exuded by the ruptured glandular trichome head. When sampling, never squeeze a floral cluster directly, as the resins will adhere to the fingers and bias further sampling. The folded paper conveniently holds the floral cluster, avoids confusion during sampling, and contains the aromas as a glass does in wine tasting.

Taste is easily sampled by loosely rolling dried floral clusters in a cigarette paper and inhaling to draw a taste across the tongue. Samples should be approximately the same size.

Taste in Cannabis is divided into three categories according to usage: the taste of the aromatic components carried by air that passes over the Cannabis when it is inhaled without being lighted; the taste of the smoke from burning Cannabis; and the taste of Cannabis when it is consumed orally. These three are separate entities.

The terpenes contained in a taste of unlighted Cannabis are the same as those sensed in the aroma, but perceived through the sense of taste instead of smell. Orally ingested Cannabis generally tastes bitter due to the vegetative plant tissues, but the resin is characteristically spicy and hot, somewhat like cinnamon or pepper. The taste of Cannabis smoke is determined by the burning tissues and vaporizing terpenes. These terpenes may not be detected in the aroma and unlighted taste.

Biosynthetic relationships between terpenes and cannabinoids have been firmly established. Indeed, cannabinoids are synthesized within the plant from terpene precursors. It is suspected that changes in aromatic terpene levels parallel changes in cannabinoid levels during maturation. As connections between aroma and psychoactivity are uncovered, the breeder will be better able to make field selections of prospective high-THC parents without complicated analysis.

Persistence of Aromatic Principles and Cannabinoids

Cannabis resins deteriorate as they age, and the aromatic principles and cannabinoids break down slowly until they are hardly noticeable. Since fresh Cannabis is only available once a year in temperate regions, an important breeding goal has been a strain that keeps well when packaged. Packageability and shelf life are important considerations in the breeding of fresh fruit species and will prove equally important if trade in Cannabis develops after legalization.

Trichome Type

Several types of trichomes are present on the epidermal surfaces of Cannabis. Several of these trichomes are glandular and secretory in nature and are divided into bulbous, capitate sessile, and capitate stalked types. Of these, the capitate stalked glandular trichomes are apparently responsible for the intense secretion of cannabinoid laden resins. Plants with a high density of capitate stalked trichomes are a logical goal for breeders of Cannabis. The number and type of trichomes is easily characterized by observation with a small hand lens (lOX to 50X). Recent research by V. P. Soroka (1979) concludes that a positive correlation exists between the number of glandular trichomes on leaves and calyxes and the various cannabinoid contents of the floral clusters. In other words, many capitate stalked trichomes means higher THC levels.

Resin Quantity and Quality

Resin production by the glandular trichomes varies. A strain may have many glandular trichomes but they may not secrete very much resin. Resin color also varies from strain to strain. Resin heads may darken and become more opaque as they mature, as suggested by several authors. Some strains, however, produce fresh resins that are transparent amber instead of clear and colorless, and these are often some of the most psychoactive strains. Transparent resins, regardless of color, are a sign that the plant is actively carrying out resin biosynthesis. When biosynthesis ceases, resins turn opaque as cannabinoid and aromatic levels decline. Resin color is certainly an indication of the conditions inside the resin head, and this may prove to be another important criterion for breeding.

Resin Tenacity

For years strains have been bred for hashish production. Hashish is formed from detached resin heads. In modern times it might be feasible to breed a strain with high resin production that gives up its precious covering of resin heads with only moderate shaking, rather than the customary flailing that also breaks up the plant. This would facilitate hashish production. Strains that are bred for use as marijuana would benefit from extremely tenacious resin heads that would not fall off during pacing and shipment.

Drying and Curing Rate

The rate and extent to which Cannabis dries is generally determined by the way it is dried, but, all conditions being the same, some strains dry much more rapidly and completely than others. It is assumed that resin has a role in preventing desiccation and high resin content might retard drying. However, it is misconception that resin is secreted to coat and seal the surface of the calyxes and leaves. Resin is secreted by glandular trichomes, but they are trapped under a cuticle layer surrounding the head cells of the trichome holding the resin away from the surface of the leaves. There it would rarely if ever have a chance to seal the surface of the epidermal layer and prevent the transpiration of water. It seems that an alternate reason must be found for the great variations in rate and extent of drying. Strains may be bred that dry and cure rapidly to save valuable time.

Ease of Manicuring

One of the most time-consuming aspects of commercial Cannabis production is the seemingly endless chore of manicuring, or removing the larger leaves from the floral clusters. These larger outer leaves are not nearly as psychoactive as the inner leaves and calyxes, so they are usually removed before selling as marijuana. Strains with fewer leaves obviously require less time to manicure. Long petioles on the leaves facilitate removal by hand with a small pair of scissors. If there is a marked size difference between very large outer leaves and tiny, resinous inner leaves it is easier to manicure quickly because it is easier to see which leaves to remove.

Seed Characteristics

Seeds may be bred for many characteristics including size, oil content, and protein content. Cannabis seed is a valuable source of drying oils, and Cannabis-seed cake is a fine feed for ranch animals. Higher-protein varieties may be developed for food. Also, seeds are selected for rapid germination rate.

Maturation

Cannabis strains differ greatly as to when they mature and how they respond to changing environment. Some strains, such as Mexican and Hindu Kush, are famous for early maturation, and others, such as Colombian and Thai, are stubborn in maturing and nearly always finish late, if at all. Imported strains are usually characterized as either early, average, or late in maturing; however, a particular strain may produce some individuals which mature early and others which mature late. Through selection, breeders have, on the one hand, developed strains that mature in four weeks, outdoors under temperate conditions; and on the other hand, they have developed greenhouse strains that mature in up to four months in their protected environment. Early maturation is extremely advantageous to growers who live in areas of late spring and early fall freezes. Consequently, especially early-maturing plants are selected as parents for future early-maturing strains.

Flowering

Once a plant matures and begins to bear flowers it may reach peak floral production in a few weeks, or the floral clusters may continue to grow and develop for several months. The rate at which a strain flowers is independent of the rate at which it matures, so a plant may wait until late in the season to flower and then grow extensive, mature floral clusters in only a few weeks.

Ripening

Ripening of Cannabis flowers is the final step in their maturation process Floral clusters will usually mature and ripen in rapid succession, but sometimes large floral clusters will form and only after a period of apparent hesitation will the flowers begin to produce resin and ripen. Once ripening starts it usually spreads over the entire plant, but some strains, such as those from Thailand, are known to ripen a few floral clusters at a time over several months. Some fruit trees are similarly everbearing with a yearlong season of production. Possibly Cannabis strains could be bred that are true everbearing perennials that continue to flower and mature consistently all year long.

Cannabinoid Profile

It is supposed that variations in the type of high associated with different strains of Cannabis result from varying levels of cannabinoids. THC is the primary psychoactive ingredient which is acted upon synergistically by small amounts of CBN, CBD, and other accessory cannabinoids. We know that cannabinoid levels may be used to establish cannabinoid phenotypes and that these phenotypes are passed on from parent to offspring. Therefore, cannabinoid levels are in part determined by genes. To accurately characterize highs from various individuals and establish criteria for breeding strains with particular cannabinoid contents, an accurate and easy method is necessary for measuring cannabinoid levels in prospective parents. Various combinations of these traits are possible and inevitable. The traits that we most often see are most likely dominant and any effort to alter genetics and improve Cannabis strains are most easily accomplished by concentrating on the major phenotypes for the most important traits. The best breeders set high goals of a limited scope and adhere to their ideals.