Cannabaceae
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Cannabaceae is a small family of flowering plants in the order Rosales, containing about 170 species across approximately ten currently accepted genera.[1][2] The family includes the herbaceous genera Cannabis (hemp) and Humulus (hops), which are its most economically important members, alongside the woody genera Celtis (hackberries), Trema, Aphananthe, Chaetachme, Gironniera, Lozanella, Parasponia and Pteroceltis. It is sometimes called the hemp family.
The family is recognised in its present, expanded form only since the early 2000s. Earlier botanists placed Cannabis and Humulus variously in Urticaceae or Moraceae, and the remaining genera in a separate family Celtidaceae. Molecular phylogenetic analyses of plastid DNA in the late 1990s and early 2000s showed that Cannabis and Humulus are nested within former Celtidaceae genera, and that the combined group is best treated as a single family.[3][4] Under priority rules, Cannabaceae, the older family name, was retained.
Few morphological characters apply to every member of the family. Cannabaceae includes trees, shrubs, erect herbs and twining vines; leaves may be alternate, opposite or both on the same plant; and fruits may be drupes, samaras or achenes. The family is held together by molecular evidence and a small set of supporting characters including usually unisexual and inconspicuous flowers, antitepalous stamens, the presence of stipules and diporate or triporate pollen.[5][2]
Taxonomy and circumscription
History before molecular methods
The Italian botanist Andrea Cesalpino first grouped Cannabis with its sister genus Humulus in 1583, on the basis of similarities in their flowers and fruits.[4] Before this, Cannabis had been classified with phylogenetically unrelated plants on the basis of leaf shape and human use.
Eighteenth-century botanists oscillated between treatments. Michel Adanson grouped Cannabis, Humulus and Celtis together in 1763. Jean-Baptiste Lamarck placed Cannabis and Humulus in the mulberry family Moraceae in 1788. Antoine Laurent de Jussieu placed both in Urticaceae in 1789. The Russian botanist Ivan Ivanovich Martynov coined the family name Cannabaceae in 1820, raising Cannabis and Humulus to family rank.[4] Subsequent botanists, unaware of Martynov, coined the synonymous names Cannabineae (Endlicher, 1837) and Cannabinaceae (Lindley, 1846); both are now treated as orthographic variants.
Through the nineteenth and early twentieth centuries most authorities continued to place Cannabis and Humulus inside Urticaceae or Moraceae rather than as a separate family. George Bentham and Joseph Dalton Hooker treated them as the tribe Cannabineae within Urticaceae in 1880; Adolf Engler and Karl Prantl placed them as the subfamily Cannaboideae of Moraceae in 1889.[4] Alfred Barton Rendle re-separated Cannabaceae from Moraceae in 1925, an interpretation that became broadly accepted after Arthur Cronquist adopted it in his angiosperm classification in 1968.[4]
Modern expanded family
The current circumscription of Cannabaceae dates to the early 2000s. Plastid DNA evidence accumulated through the 1990s showed that Cannabis and Humulus are nested within the genera then placed in the family Celtidaceae. Kenneth Sytsma and colleagues placed the question on a firmer footing in 2002, using sequences of the plastid markers rbcL, trnL-F and ndhF across a wide sampling of the urticalean group, and concluded that the expanded family should be called Cannabaceae on grounds of nomenclatural priority.[3]
The Angiosperm Phylogeny Group adopted the expanded Cannabaceae in APG III (2003), and confirmed it in APG IV (2016), where the family is placed in the order Rosales with ten genera.[1] Subsequent estimates of total species number range from about 117 to about 170, depending on the treatment of the variable genera Trema, Parasponia and Celtis.[6][2]
Phylogeny and relationships
Within Rosales, Cannabaceae is sister to a clade containing Moraceae and Urticaceae. Together these three families form an informal group often called the urticalean rosids.[3] Earlier authors recognised a separate order Urticales for the same lineage, but molecular evidence places the group inside Rosales rather than as its own order.[3][1]
Intergeneric relationships within the family were resolved in stages. Mei-Qing Yang and colleagues sampled all ten currently recognised genera in 2013 using four plastid loci, and reported three findings that have held up in later studies.[2] First, the expanded family is strongly supported as monophyletic. Second, Aphananthe is sister to all other genera, occupying the deepest branch within the family. Third, Trema is paraphyletic with respect to Parasponia; the two are not consistently separable as distinct genera on molecular criteria, and some authors merge them. Cannabis and Humulus form a strongly supported clade nested within the remaining woody genera.
A larger phylogenomic analysis by Xiao-Gang Fu and colleagues in 2023 used Hyb-Seq sequence capture of 90 nuclear genes and 82 plastid loci across 82 species, and confirmed the broad pattern while revealing deep cyto-nuclear discordance attributable to incomplete lineage sorting and gene flow.[7] All genera were recovered as monophyletic with the exception of Celtis, which split into two clades; the authors proposed treating one clade as the new genus Sparrea on the basis of both molecular and morphological evidence. This proposal is recent and has yet to be uniformly adopted.[7]
Genera
Ten genera are currently accepted in Cannabaceae. Species totals are approximate and vary across sources.[2][6][1]
Aphananthe (five species) is sister to all other Cannabaceae and is distributed disjunctly across Madagascar, southwestern China to Japan, Malesia, eastern Australia and Mexico. Lozanella (two species) is restricted to tropical America and is distinctive in having opposite leaves. Gironniera (six species) ranges from Malesia to the Pacific. Celtis (about 73 to 100 species), known as hackberries or nettle trees, is the largest genus in the family and is widely distributed across temperate and tropical regions. Pteroceltis tatarinowii, the sole species of Pteroceltis, is restricted to northern and central China.
Chaetachme aristata, the sole species of Chaetachme, occurs in tropical and southern Africa and Madagascar. Trema (about twelve to forty species, depending on whether Parasponia is included) is the family's most widely distributed tropical and warm-temperate genus. Parasponia (about five species) is restricted to Malesia and the western Pacific and is closely related to, possibly nested within, Trema.[2]
The two herbaceous genera lie in a derived position. Humulus includes three species, of which the common hop Humulus lupulus is by far the most economically important; the others are Humulus japonicus and Humulus yunnanensis. Cannabis is variously treated as one polymorphic species (Cannabis sativa L.) with several subspecies, or as up to three species, including Cannabis indica and Cannabis ruderalis; for a fuller discussion see Cannabis taxonomy.[4][8]
Morphology
Cannabaceae shows considerable morphological diversity, and Yang and colleagues noted that clear morphological synapomorphies for the family as a whole are difficult to identify.[2] A set of supporting characters used in identification keys includes usually unisexual and inconspicuous flowers, antitepalous stamens, the presence of stipules, diporate or triporate pollen and free filaments slightly adnate to the tepals.[5] Cystoliths are present in many members.
Habit varies widely. Most genera, including Celtis, Trema, Aphananthe, Pteroceltis, Chaetachme, Gironniera, Lozanella and Parasponia, are woody, ranging from shrubs to medium-sized trees. Cannabis is an erect annual herb. Humulus is a perennial herbaceous vine that climbs by twining.
Leaves are alternate in most genera, opposite in Lozanella and both alternate and opposite on the same plant in Cannabis and Humulus.[2] Stipules are always present, and palmate lobing or compounding of leaves is widespread.
Flowers are small, regular and lack petals or have them very reduced; wind pollination is the rule, and the small inconspicuous flowers reflect this. Fruit types differ between genera: drupes are the ancestral state and persist in most woody members, samaras occur in Pteroceltis, and achenes in Cannabis and Humulus.[2]
Distribution and biogeography
Cannabaceae is cosmopolitan. The aggregate range covers Northern Hemisphere temperate zones for Humulus and Cannabis, temperate and tropical regions worldwide for Celtis and Trema, and various Old and New World tropics for the smaller genera.[2]
Jian-Jun Jin and colleagues reconstructed the historical biogeography of the family in 2020.[9] They placed the family's origin in the Late Cretaceous, with Cannabaceae-typical pollen recorded from the Turonian, approximately 94 to 90 million years ago, in deposits from Sarawak in Borneo. The early Cenozoic distribution was strongly Northern Hemisphere; later range shifts brought several lineages into tropical regions as climates changed. Long-distance dispersal, rather than tectonic vicariance, accounts for most of the family's current distribution, and the authors describe Cannabaceae as "born migrators" on the strength of repeated transoceanic dispersal events across the Cenozoic.[9]
Yun-Xia Li and colleagues examined diversification rates across the family in 2025 and found that temperate lineages have speciated faster than tropical lineages, consistent with the broader rosid pattern of temperate-zone radiation during Cenozoic cooling.[10] The pattern likely reflects pre-adaptation to seasonal climates in some lineages, the availability of newly opened temperate biomes and divergence into novel climatic niches.
Reproductive and symbiotic biology
Sexual systems vary across Cannabaceae. Yang and colleagues reconstructed the ancestral state as monoecy, with multiple shifts to dioecy along the tree.[2] Cannabis and Humulus are both dioecious, a state that may have arisen in their common ancestor. Polygamous and andromonoecious systems occur elsewhere in the family.
All members are wind-pollinated. Reduced, unornamented flowers and large amounts of small dry pollen are consistent with this strategy, and pollen of Cannabaceae is among the more abundant types in palynological records of temperate and tropical environments.
Most genera, including Cannabis, form mycorrhizal associations with arbuscular mycorrhizal fungi. Parasponia is exceptional among the angiosperms: it is the only non-legume lineage that establishes nitrogen-fixing nodules with rhizobial bacteria, a symbiosis otherwise restricted to the legume family Fabaceae.[11] Phylogenomic analyses indicate that this nodulation trait shares a single deep evolutionary origin in the nitrogen-fixing clade and has been retained in Parasponia but lost in other Cannabaceae.
Phytochemistry
The two herbaceous genera Cannabis and Humulus share elaborate glandular trichomes that secrete prenylated phenolic compounds. In Cannabis the principal products are the cannabinoids; in Humulus they are the bitter acids (humulones and lupulones) and prenylated flavonoids such as xanthohumol. The biosynthetic pathways are related, and the close chemical kinship of the two genera reflects their shared ancestry.[4]
Cannabinoids in their fully developed form appear to be unique to Cannabis within the family; no other genus is known to produce the same series of molecules.[4] Other family members produce various flavonoids, alkaloids and terpenes, but at lower concentrations and without the specialised trichome architecture seen in Cannabis and Humulus.
Fossil record
The earliest Cannabaceae-typical pollen, from the Turonian of Borneo, indicates that the family was already differentiated by approximately 90 million years ago.[9] Pollen records become more frequent through the Cenozoic and document the family's repeated dispersal across continents.
Macrofossils are less common. The extinct genus Dorofeevia (formerly known as Humularia), described from Oligocene deposits in central Siberia, has been interpreted as a sister lineage of Cannabis and Humulus that diverged roughly twenty million years before going extinct.[4] Cannabis-specific macrofossils are rare; only three are known worldwide, and the genus's deeper history is largely inferred from molecular clock estimates and fossil pollen analysis.[4]
Economic and cultural importance
Two members account for most of the family's modern economic significance. Cannabis sativa is grown for fibre, seed, oil, leaf and the cannabinoid-rich resinous female inflorescences used for medicinal and drug-type purposes; the species and its taxonomy are treated in detail in Cannabis sativa and Cannabis taxonomy. Humulus lupulus is grown for its dried female cones (hops), which provide bitterness, aroma and antimicrobial preservation in beer; hops dominate the commercial output of the genus, and the brewing industry accounts for the great majority of the global harvest.[4]
Several woody genera have local importance. Many Celtis species are grown for landscaping and ornamental purposes, and some produce edible drupes. The bark of Pteroceltis tatarinowii is the raw material for traditional Xuan paper, a high-quality Chinese paper used for calligraphy and ink painting. Various species of Trema and Gironniera have local timber, pulp and traditional medicinal uses across tropical Asia, Africa and the Pacific.
Parasponia is of scientific rather than commercial significance, as the only non-legume rhizobial symbiont and a comparative model for understanding the evolution and possible engineering of nitrogen-fixing nodulation in crops.[11]
See also
References
- ↑ 1.0 1.1 1.2 1.3 The Angiosperm Phylogeny Group, Chase, M.W., Christenhusz, M.J.M., Fay, M.F., Byng, J.W., Judd, W.S., Soltis, D.E., Mabberley, D.J., Sennikov, A.N., Soltis, P.S. & Stevens, P.F. (2016). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. Botanical Journal of the Linnean Society, 181(1), 1–20. doi:10.1111/boj.12385
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 Yang, M.Q., van Velzen, R., Bakker, F.T., Sattarian, A., Li, D.Z. & Yi, T.S. (2013). Molecular phylogenetics and character evolution of Cannabaceae. Taxon, 62(3), 473–485. doi:10.12705/623.9
- ↑ 3.0 3.1 3.2 3.3 Sytsma, K.J., Morawetz, J., Pires, J.C., Nepokroeff, M., Conti, E., Zjhra, M., Hall, J.C. & Chase, M.W. (2002). Urticalean rosids: circumscription, rosid ancestry, and phylogenetics based on rbcL, trnL-F, and ndhF sequences. American Journal of Botany, 89(9), 1531–1546. doi:10.3732/ajb.89.9.1531
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 McPartland, J.M. (2018). Cannabis systematics at the levels of family, genus, and species. Cannabis and Cannabinoid Research, 3(1), 203–212. doi:10.1089/can.2018.0039
- ↑ 5.0 5.1 Judd, W.S., Campbell, C.S., Kellogg, E.A., Stevens, P.F. & Donoghue, M.J. (2008). Plant Systematics: A Phylogenetic Approach, 3rd edition. Sinauer Associates, Sunderland, Massachusetts.
- ↑ 6.0 6.1 Zhang, H.L., Jin, J.J., Moore, M.J., Yi, T.S. & Li, D.Z. (2018). Plastome characteristics of Cannabaceae. Plant Diversity, 40(3), 127–137. doi:10.1016/j.pld.2018.04.003
- ↑ 7.0 7.1 Fu, X.G., Liu, S.Y., van Velzen, R., Stull, G.W., Tian, Q., Li, Y.X., Folk, R.A., Guralnick, R.P., Kates, H.R., Jin, J.J., Li, Z.H., Soltis, D.E., Soltis, P.S. & Yi, T.S. (2023). Phylogenomic analysis of the hemp family (Cannabaceae) reveals deep cyto-nuclear discordance and provides new insights into generic relationships. Journal of Systematics and Evolution, 61(5), 806–826. doi:10.1111/jse.12920
- ↑ McPartland, J.M. (2020). Cannabis: the plant, its evolution, and its genetics — with an emphasis on Italy. Rendiconti Lincei. Scienze Fisiche e Naturali, 31(3), 445–455. doi:10.1007/s12210-020-00962-2
- ↑ 9.0 9.1 9.2 Jin, J.J., Yang, M.Q., Fritsch, P.W., van Velzen, R., Li, D.Z. & Yi, T.S. (2020). Born migrators: historical biogeography of the cosmopolitan family Cannabaceae. Journal of Systematics and Evolution, 58(4), 461–473. doi:10.1111/jse.12552
- ↑ Li, Y., Tian, Q., Fu, X., Condamine, F.L., Yi, T. & Onstein, R.E. (2025). Accelerated speciation in temperate Cannabaceae: the role of pre-adaptation, ecological opportunities and niche divergence. Global Ecology and Biogeography, 34(12). doi:10.1111/geb.70183
- ↑ 11.0 11.1 van Velzen, R., Holmer, R., Bu, F., Rutten, L., van Zeijl, A., Liu, W., et al. (2018). Comparative genomics of the nonlegume Parasponia reveals insights into evolution of nitrogen-fixing rhizobium symbioses. Proceedings of the National Academy of Sciences, 115(20), E4700–E4709. doi:10.1073/pnas.1721395115