Notes on determining the sex of Cannabis cultivars

Author	A. Harja	12.12.2001
	Finding out which sex cannabis plants are can be tricky and requires some knowledge of the anatomy of Cannabis flowers. Several illustrations are presented here which should make this task easier for the untrained eye.
	The Hidden Sex A cannabis plant has basically three different sexes: the pistillate (female), staminate (male) and the hermaphrodite (both female and male genes expressed in the same plant). In science lingo, cannabis is a dioecious plant. In english: cannabis plants usually express only single sex. The actual expression of sex in any cannabis plant is an very complicated outcome of intricate play of environment on a set of genetic rules. In other words, the plant has the tendency towards expressing its sex in an environment and in the same time has the possibilities for evolving into any of the three sexes.     First, lets take a look at the best way of determining the sex of an cannabis plant, the physiology of the inflorescences.   [LEFT] Cannabis sativa staminate (male) inflorenscence. Photo copyright Thomas Schoepke, used with permission from author.   Take a close look at the picture of the male flowers. Dozens of tiny sacs hang from the limbs of the flower, some of the sacs already a bit open, ready to spread the pollen, and the genes of the male. Robert Connell Clarke describes male inflorescence in Marijuana Botany:   In male flowers, five petals (approximately 5 millimeters, or 3/16 inch, long) make up the calyx and may be yellow, white, or green in color. They hang down, and five stamens (approximately 5 millimeters long) emerge, consisting of slender anthers (pollen sacs), splitting upwards from the tip and suspended on thin filaments. The exterior surface of the staminate calyx is covered with non-glandular trichomes.   In most strains of Cannabis the female plants express their sex before the males once the environmental cues that cause the flowering in the particular strain have been triggered. Tiny flowers, called primordia, appear quickly in females after the daylenght has sufficiently shortened. But the male flowers usually finish flowering and shed their pollen before the females have fully developed flowers. In other words, witten by Clarke:   "Staminate [male] plants tend to flower up to one month earlier than pistillate plants; however, pistillate plants often differentiate primordia one to two weeks before staminate (male) plants".   The Pistillate plant Female plants is what most cannabis cultivators are after. Although the primordia of the two different sexes appear very similar at first, female primordia often quickly display what is the most distinctive feature of the pistillate flowers: the two white pistils. Lets take a look at a quick and crude drawing of Pistillate Calyxes, courtesy of the author:     The pistils (1) [LEFT] are very clearly visible in this drawing of maturing female flowers. These two, usually white and 'hairy' in appearance, serve to collect any male pollen that might float by the flower. For clarity, only one flower has been rendered, although calyxes usually form in pairs on the nodes.   The Calyx (2) is the reason for the cultivation of myriad of cannabis plants - the calyx is covered with glandular trichomes, small spikes that exude resin that contains THC. A good place to start looking for the first signs of sexual differentiation of cannabis plant is at the nodes (3), intersections, right above where a branch or the stem of a leaf (petiole) is attached on the stem of the plant. During the primordia-phase these flowers are miniscule, just visible to the naked eye, in size less than few millimeters. Under the right conditions female calyxes may grow in sizes of centimeter or so in diameter.   Lets see what that wise botanist fellow R. C. Clarke has to say about the female primordia:   The females are regognized by the enlargement of a symmetrical tubular calyx (floral sheath). .. The first female calyxes tend to lack paired pistils (pollen catching appendages) though initial male flowers often mature and shed viable pollen. .. The female plants tend to be shorter and have more branches than the male. .. The female flowers appear as two long white, yellow, or pink pistils protruding frm the fold of very thin membraneous calyx. .. the calyx measures 2 to 6 millimeters in lenght.   So its either hanging tubular balls or pointy pale pistils. In any case, a magnifying glass is very useful tool for the wanna-be-cannabis-botanists.   Products of the environment Finally, lets take a closer look at the genetics and sexual behaviour of the cannabis-plants. Like I wrote earlier, cannabis is dioecious plant, meaning that only one sex is expressed per individual. But I also wrote about three sexes, mentioning the hermaphrodite. I feel that hermaphrodites are the key to understanding the behaviour of cannabis.   Like all known life, cannabis contains set of genes. These genes 'express' themselves in the plant, but only when a certain or certain group of environmental conditions are true. For instance, when the daylenght is sufficiently short its the genes that tell the plant its time to flower, to reproduce before the winter comes. Or, for instance, if certain cells in the outer surface of the plants are exposed to the correct environment they'll differentiate into roots. This is how life works on this planet.     Hermann A. Köhler's Cannabis in an beautiful chromolithography [RIGHT]. According to R. C. Clarke, an cannabis under average conditions and 'inductive photoperiod' will produce equal numbers of staminate and pistillate plants with a few hermaphodites. In my experience, I've noted and understood that each plant has a certain tendencies towards one sex or another. For instance, some strain might produce 75% female, 24% male and 1 % hermaphrodite population in a certain environment. This is very complex behaviour and I am certain it is ruled by many sets of genes. Before I go on, I'd like to note that a cannabis plant can also 'change' its sex from male or female to hermaphrodite if the environmental cues for that particular strain exist. Hermaphroditism can also be induced artificially, with an plant-hormone called gibberellic acid for instance, and if an individual of low tendency towards hermaphroditism is crossed with itself in this way, I need to add, theoretically this does not affect the genetic, inherited tendency (plant crossed with itself in this way is effectively an 'genetic carbon copy' plus some minute errors caused by the way DNA duplicates).   Any kind of stress or what could be interpreted by the plant to be a sign of impeding doom (winter) may and will cause increased male and hermaphrodite ratios. One needs to realize that the way that a cannabis plant sees its environment is very different from ours. It can sense the lenght of the day (photoperiod), direction of the light and gravity, temperature and air humidity, and the amount of the nutrients in the water the roots are in contact with. It probably has some other ways of determining which way the earth lies down. But always it will interpret any changes in the environment as if it was in the nature and as if the changes themselves were caused by changes in the nature (seasons for instance). So if the temperatures go down or the day lenght is shortened, it can mean only one thing: the winter is coming - FLOWER QUICK!! If the water is short on nutrients or the light is being shadowed by something it means - FLOWER NOW!! So to produce higher quantities of females the cultivator needs to be sure that the environment is stable and that it provides the plant with all it needs to survive. More or less an comfortable setting for the plant to grow on in. The cultivator, like noted above, also needs to make sure that the strain has full tendencies towards the expression of female character.   To conclude: The easiest way to determine the gender of an cannabis plant is to examine its flowers. To initiate flowering, most strains require 12 hours of day (=light) and 12 of night(=uninterrupted darkness). Female or Pistillate flowers are easily distinguished from the males by the long white 'pistils' protruding from the calyxii (bottom far right on the last picture). Male or Staminate inflorescences are like tiny bells hanging on the limbs of the flowers (bottom far left on the last picture).
	For more photographs of cannabis infloresces, please take a look at the Gallery two. Comments, criticism and questions welcome - A. Harja.     Marihuana Botany by Robert Connell Clarke, Ronin Publishing, Berkeley, 1st ed. 1981, for this article 10th edition was used, ISBN 0-915904-45-4.   Cannabis sativa chromolithograph by Hermann A. Köhler, 1887, from Köhler's Medizinal Pflanzen.   Special thanks to Dr. Thomas Schoepke for permission to use his photograph. See more Schoepkes photographs at http://www.plant-pictures.de/.