This review is dedicated to cannabis trichomes and their structure and functions.
- Glandular stalked trichomes
A microscope study of glandular stalked trichomes, situated on the bracts on cannabis plants shows the following correlation between trichome colour and density. It is known that glandular stalked trichomes are involved in THC production.
|2||Extremely Dense||Misty White|
|4||Moderately Dense||Opaque White|
|5||Intermediate Density||Slightly Brown|
|7||Very Scarce||Mid Brown|
|8||Extremely Scarce||Dark Brown|
According to the results the highest trichome density is when their colour is clear, while very dark colour is a sign of lack of trichomes. Darker trichomes colour is associated with lower potency and lower THC of the cannabis sample and higher CBN content. Clear trichomes contain little CBN. These results need further investigation.
- Covering thrichomes
There are also covering thrichomes, which are the first to appear on the surface of the cotyledons shortly after germination and later on on the underside of the leaves. Their main functions are to reduce water loss and protect the plant from extreme temperatures.
- Cystolythic trichomes
Cystolythic trichomes were first observed on the upper surface of the initial pair of true leaves on a cannabis seedling. They always point towards the distal part of the leaf and are typically forms from calcium oxalate or calcium carbonate crystals. Presumably their role is protection from leaf-eating predators.
- Sessile trichomes: Capitate sessile trichomes – apart from cotyledons capitate sessile trichomes are spread on other aerial surfaces throughout cannabis plant’s lifespan. By definition
these trichomes do not have stalk but in reality they have a small stalk hidden under the trichome resin head. Their stalk contains chloroplasts and could perform some photosynthetic activity. According to some plant physiologists these sub-epidermal cell structure is an “emergency” rather than a “trichome”. Their glandular head totally lack chlorophyll and they are involved in synthesis of cannabinoids and essential oils.
Antherial sessile trichomes – these trichomes are observed on cannabis anthers. They are usually located on the calix surrounding these anthers and are larger in size.
Capitate stalked trichomes
They are present on the calyx, bracteoles, bracts and accompanying petioles of female cannabis plants. Capitate stalked trichomes are rarely observed on male plants. These trichomes are active during the earlier stages of development. They have opaque-white colour and coloration in later stages (brown colour) is possibly due to necrosis of there inactive now tissues. This browning will continue after the cannabis plant is harvested and dried. They are involved in THCA, monoterpenes and sesquiterpenes synthesis although their functions are not completely studied there are results suggesting that they have the highest cannabinoid content. It is common during the ageing process the trichome heads to be detached.
According to of the theories capitate stalked trichomes act like a physical barrier to small insects.
They are the smallest of the glandular trichomes and could be seen first on the stem and lower leaves. Their function is not known but there is a hypothesis that they are involved in CBGA synthesis, although they do not contain significant concentration of cannabinoids.
Bulbous trichomes are the first ones to turn brown when the plant ages. This coloration continues during storage at room temperatures.