Achene
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An achene is the fruit of Cannabis: a small, dry fruit that holds one seed and does not split open when ripe. What is sold, sown and stored as hemp seed or cannabis seed is botanically the whole achene.[1][2] The achene develops from the ovary of the female flower.[3] Its fruit wall, the pericarp, and the seed coat inside it are tissues of the mother plant.[1]
In wild plants the ripe achene is small, keeps a thin mottled covering left from the flower and falls from the plant at a break-point in its base. Domesticated plants bear larger achenes, mostly bare and blunt at the base, that stay on the plant.[4][5] Achenes recovered from tombs in China have been measured and compared on these characters to judge whether the plants that bore them were cultivated.[6]
From flower to fruit
The female flower of Cannabis is enclosed in a small leafy bract, the perigonal bract, which later encloses the achene.[5] The bract carries glandular trichomes.[1] It is also called the bracteole or perigonium. The name calyx is also used, one McPartland and Small consider inappropriate.[5] Inside it, the flower's own perianth is a thin membrane that forms no corolla and clings to the outer surface of the developing fruit.[5]
Prakash, Bohm and Maze followed the achene from the ovary to the ripe fruit in four varieties of C. sativa (sativa, spontanea, indica and kafiristanica). Soon after fertilisation the nucellus curves strongly, so that the campylotropous ovule takes an ana-amphitropous form. The ripe embryo lies curved inside the seed. Compared stage by stage, the four varieties showed no significant difference in how the achene develops.[3]
Fruit wall and seed coat
A ripe achene has up to three coverings round the embryo: what remains of the perianth, the pericarp and the seed coat (testa).[5][3] The perianth persists over the whole fruit in wild-type plants and is mostly shed in domesticated ones. Where it has fallen away, the outer surface of the pericarp shows a network of veins.[5]
The pericarp has three layers: an outer exocarp (also called the epicarp), a mesocarp and an inner endocarp.[6] The endocarp changes most as the fruit develops. Its cells grow much larger and their walls thicken, while the layer above it and the epicarp thicken their walls without their cells growing.[3] Naraine and colleagues tested the pericarp's resistance to fracture alongside the form of the achene in ruderal, fibre, oilseed and marijuana plants.[2]
The seed coat is thin. Chloroplasts form in it soon after the embryo reaches the globular stage. It has little or no protective role in the dispersed fruit.[3] Li and colleagues divide the achene into a hull and a kernel, the kernel holding the radicle, endosperm and cotyledons. The hull is the part discarded when hemp seed is processed into oil, flour and protein powder.[7]
Tissue of the mother plant
The pericarp and the seed coat are maternal tissue: the seed coat differentiates from the integuments of the ovule, which belong to the mother plant. Seed size is set by both maternal and zygotic factors and by the interaction between them.[1] In a cross between SI-1, a tall Chinese variety with large seeds, and IPK_CAN_57, a short Syrian landrace with small ones, the first-generation seeds borne on the Syrian mother closely resembled the mother's own. One generation later, seeds borne on first-generation mothers were intermediate in size between the two original parents.[1] Manansala-Siazon and colleagues read this as agreeing with the idea that the seed coat, formed from maternal tissue, can set an upper limit to seed size.[1]
Embryo and stored food
The ripe embryo is curved, has two cotyledons and fills most of the seed. The cotyledons enclose a set of well-formed first leaves. Food is stored in the cells of the radicle and the cotyledons and in the endosperm, which is one to several cell layers thick depending on where in the seed it lies.[3]
By weight, hemp seed holds about 35–36 per cent oil, 24–26 per cent protein and 27–29 per cent carbohydrate.[1] In achenes from 20 Chinese landraces, Li and colleagues found that most of the compounds differing between hull and kernel were more concentrated in the hull. Imaging of sectioned achenes showed cannabinoids in the hull and also in the cotyledons.[7]
Shedding and dispersal
Wild-type achenes fall when ripe. They separate from the plant at an abscission zone in the base, which is drawn out into a short tapered stub.[5] In domesticated plants the abscission zone is reduced and the achenes are not shed (the loss of seed shattering). Their achenes are larger and their perianth adheres less.[5] In var. afghanica the ripe achenes stay on the plant, trapped by the dense parts of the infructescence round them.[5] McPartland and Small, following Zinger's description of 1898, call the mottling of the persistent perianth camouflage.[5] Small (1975) took the small size, adhering perianth and elongated base of wild achenes to be adaptive in wild plants.[4]
The USDA hemp phenotyping protocol measures shattering on the living plant. It encloses the top 30 centimetres of a seed-bearing raceme in a pollination bag about five weeks after the female plant's terminal flowering. When the plant has senesced and dried, the seed lying loose in the bag is weighed against all the seed from that length of raceme; the ratio is the shatter fraction.[8]
In a study of naturalised hemp in east-central Illinois, Haney and Kutscheid found that many birds and probably small mammals eat the seed, doves and bobwhite quail among them. They judged that the seed was spread little except by people and that viable seed lasted no more than two or three years in the soil, unlike the long-lived or bird- and wind-spread seed of most other weedy annuals.[9]
Achenes in archaeology
Two tombs of the Western Han dynasty at Laoguanshan Cemetery in Chengdu held 116,940 and 3,660 whole fruits, radiocarbon dated to 2115–1930 cal. BP. Their pericarps kept all three layers, the endocarp of large thick-walled cells with dense knob-like protrusions on its inner face. Of the seed inside only the membranous seed coat remained, its surface marked by rows of crater-like pits.[6] The fruits of one tomb were larger and had neither a perianth nor an elongated base. Those of the other were smaller and had a slightly drawn-out base. Bai and colleagues judged the first closer to cultivated fruits and the second closer to wild ones.[6]
At Jiayi Cemetery in Turpan, 13 nearly whole female plants about 2,800 to 2,400 years old had been laid over the body of a man. Each fruit was still covered by its perianth inside a pointed bract. The achenes are oval, flattened and two-ribbed, 2.3 to 2.7 millimetres long and 1.8 to 2.2 millimetres wide, their surface finely veined beneath the perianth.[10] In the main tomb of the Haihun Marquis cemetery at Nanchang, a pile of waterlogged hemp achenes lay in the grain store beside husked rice and foxtail millet. Only their seed coats survive, 3.3 to 5.0 millimetres long and 2.6 to 3.7 millimetres wide.[11]
See also
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Manansala-Siazon, S.E.; Siazon, P.M.; Tandayu, E.; Garcia-de Heer, L.; Burn, A.; et al. (2025). "Seed the difference: QTL mapping reveals several major loci for seed size in Cannabis sativa L." Plants. 14 (24) 3853. doi:10.3390/plants14243853. PMC 12737016.
- ↑ 2.0 2.1 Naraine, S.G.U.; Small, E.; Laursen, A.E.; Campbell, L.G. (2020). "A multivariate analysis of morphological divergence of "seeds" (achenes) among ruderal, fibre, oilseed, dioecious/monoecious and marijuana variants of Cannabis sativa L.". Genetic Resources and Crop Evolution. 67 (3): 703–714. doi:10.1007/s10722-019-00848-9.
- ↑ 3.0 3.1 3.2 3.3 3.4 3.5 Prakash, N.; Bohm, Lesley R.; Maze, Jack (1979). "Developmental anatomy of the achene in Cannabis". Canadian Journal of Botany. 57 (11): 1243–1251. doi:10.1139/b79-152.
- ↑ 4.0 4.1 Small, Ernest (1975). "Morphological variation of achenes of Cannabis". Canadian Journal of Botany. 53 (10): 978–987. doi:10.1139/b75-117.
- ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 McPartland, J.M.; Small, E. (2020). "A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives". PhytoKeys. 144: 81–112. doi:10.3897/phytokeys.144.46700.
- ↑ 6.0 6.1 6.2 6.3 Bai, Yunjun; Jiang, Ming; Xie, Tao; Jiang, Chao; Gu, Man; Zhou, Xinying; Yan, Xue; Yuan, Yuan; Huang, Luqi (2021). "Archaeobotanical evidence of the use of medicinal cannabis in a secular context unearthed from south China". Journal of Ethnopharmacology. 275 114114. doi:10.1016/j.jep.2021.114114.
- ↑ 7.0 7.1 Li, Jun; Wang, Sijia; Wan, Huihua; He, Ruikun; Li, Zhen; An, Ruofan; Yue, Zhongbao; Mi, Yaolei; Chen, Weiqiang; Cao, Xue; Wang, Sifan; Xu, Zhichao; Zhu, Lingjuan; Ma, Wei; Chen, Shilin; Sun, Wei; Yang, Wei (2026). "Metabolomic diversity and spatial localization of bioactive compounds in hemp achenes from diverse landraces". Journal of Pharmaceutical Analysis. 16 (9) 101545. doi:10.1016/j.jpha.2025.101545. PMC 13571719.
- ↑ Stansell, Z.; Barraco, A.; et al., eds. (16 December 2025). USDA Hemp Phenotyping and Protocol Handbook, Version 4 (Report). United States Department of Agriculture.
- ↑ Haney, Alan; Kutscheid, Benjamin B. (January 1975). "An ecological study of naturalized hemp (Cannabis sativa L.) in east-central Illinois". The American Midland Naturalist. 93 (1): 1–24. doi:10.2307/2424101.
- ↑ Jiang, Hongen; Wang, Long; Merlin, Mark D.; Clarke, Robert C.; Pan, Yan; Zhang, Yong; Xiao, Guoqiang; Ding, Xiaolian (2016). "Ancient Cannabis burial shroud in a Central Eurasian cemetery". Economic Botany. 70 (3): 213–221. doi:10.1007/s12231-016-9351-1.
- ↑ Jiang, Hongen; Yang, Jun; Liang, Tongjun; Zhang, Zhiyong; Wang, Shuzhi; Qi, Xuekai; Sheng, Pengfei (2021). "Palaeoethnobotanical analysis of plant remains discovered in the graveyard of the Haihun Marquis, Nanchang, China". Vegetation History and Archaeobotany. 30 (1): 119–135. doi:10.1007/s00334-020-00821-y.