|Leaves and immature fruit of Chinese hackberry ( C. sinensis)|
Some 60–70 (see about 35 below)
Celtis is a genus of about 60–70 species of deciduous trees, commonly known as hackberries or nettle trees, widespread in warm temperate regions of the Northern Hemisphere, in southern Europe, southern and eastern Asia, and southern and central North America, south to central Africa, and northern and central South America. The genus is present in the fossil record at least since the Miocene of Europe, and Paleocene of North America and eastern Asia.   
Previously included either in the elm family ( Ulmaceae) or a separate family, Celtidaceae, the APG III system places Celtis in an expanded hemp family ( Cannabaceae).   The generic name originated in Latin and was applied by Pliny the Elder to the unrelated Ziziphus lotus. 
Celtis species are generally medium-sized trees, reaching 10–25 m (35–80 ft) tall, rarely up to 40 m (130 ft) tall. The leaves are alternate, simple, 3–15 cm (1 1⁄4–6 in) long, ovate- acuminate, and evenly serrated margins. Diagnostically, Celtis can be very similar to trees in the Rosaceae and other rose motif families.
- Celtis africana Burm.f. – white stinkwood (Afrotropical region)
- Celtis australis L. – European hackberry, European nettle tree, or lote tree
- Celtis balansae Planch. (New Caledonia (Australia))
- Celtis biondii Pamp.
- Celtis brasiliensis Planch.
- Celtis bungeana L. – Bunge's hackberry
- Celtis caucasica L. – Caucasian hackberry
- Celtis conferta Planch. – cottonwood
- Celtis durandii Engl.
- Celtis ehrenbergiana (Klotzsch) Liebm. – spiny hackberry, granjeno (Spanish) (southern US, Mexico, Greater Antilles, northern South America)
- Celtis hypoleuca Planch. (New Caledonia (Australia))
- Celtis iguanaea (Jacq.) Sarg. – iguana hackberry (Florida (US), Mexico, Caribbean, Central and South America)
- Celtis integrifolia L. – African hackberry
- Celtis jessoensis Koidz. – Japanese hackberry (Japan & Korea)
- Celtis koraiensis L. – Korean hackberry
- Celtis labilis L. – Hubei hackberry
- Celtis laevigata Willd. – southern or sugar hackberry (southern US, Texas), sugarberry (eastern USA, northeastern Mexico)
- Celtis lindheimeri Engelm. ex K.Koch – Lindheimer's hackberry (Texas (US), Coahuila (Mexico))
- Celtis loxensis C.C.Berg
- Celtis luzonica Warb. (Philippines)
- Celtis mildbraedii Engl.
- Celtis occidentalis L. – common or northern hackberry, false elm (eastern North America)
- Celtis pallida Torr. – desert or shiny hackberry (southwestern US / Texas, northern Mexico)
- Celtis paniculata (Endl.) Planch. – whitewood (eastern Malesia, eastern Australia, Micronesia, western Polynesia)
- Celtis philippensis Planch.
- Celtis planchoniana K.I.Chr. (eastern Europe and western Asia)
- Celtis reticulata Torr. – netleaf hackberry (western North America)
- Celtis schippii Standl.
- Celtis sinensis Pers. – Chinese or Japanese hackberry, Chinese nettle tree (China and Japan)
- Celtis tala Gillet ex Planch. – tala (South America)
- Celtis tenuifolia Nutt. – dwarf hackberry (North America)
- Celtis tetranda Roxb.
- Celtis timorensis Span. – kayu busok
- Celtis tournefortii L. – Oriental hackberry
- Celtis trinervia Lam. – almex
- Trema cannabina Lour. (as C. amboinensis Willd.)
- Trema lamarckiana (Schult.) Blume (as C. lamarckiana Schult.)
- Trema orientalis (L.) Blume (as C. guineensis Schumach. or C. orientalis L.)
- Trema tomentosa (Roxb.) H.Hara (as C. aspera Brongn. or C. tomentosa Roxb.) 
Several species are grown as ornamental trees, valued for their drought tolerance. They are a regular feature of arboreta and botanical gardens, particularly in North America. Chinese hackberry ( C. sinensis) is suited for bonsai culture, while a magnificent specimen in Daegu-myeon is one of the natural monuments of South Korea. Some, including common hackberry ( C. occidentalis) and C. brasiliensis, are honey plants and pollen source for honeybees of lesser importance. Hackberry wood is sometimes used in cabinetry and woodworking.
The berries are often eaten locally. The Korean tea gamro cha (감로차, 甘露茶) contains C. sinensis leaves.
Celtis species are used as food plants by the caterpillars of certain Lepidoptera. These include mainly brush-footed butterflies, most importantly the distinct genus Libythea (beak butterflies) and some Apaturinae (emperor butterflies):
- Acytolepis puspa – common hedge blue, recorded on Chinese hackberry ( C. sinensis)
- Automeris io – Io moth, recorded on southern hackberry (C. laevigata)
- Asterocampa celtis – hackberry butterfly or hackberry emperor
- Libythea celtis – European beak
- Libythea labdaca – African beak
- Libythea lepita – common beak
- Libythea myrrha – club beak, recorded on C. tetrandra  
- Libytheana carinenta – American snout or common snout butterfly
- Nymphalis xanthomelas – scarce tortoiseshell, recorded on European hackberry (C. australis)
- Sasakia charonda – great purple emperor, recorded on C. jessoensis and C. japonica
- A putative new taxon of the two-barred flasher (Astraptes fulgerator) cryptic species complex, provisionally called "CELT," has hitherto only been found on C. iguanaea.  
- Keeler, Harriet L. (1900). Our Native Trees and How to Identify Them. Originally published by Charles Scribner's Sons, New York. Facsimile edition from a scan of the first edition published 2005 by the Kent State University Press, Ohio. ISBN 0873388380. Available online through Google Books. , pp.249–252.
- MacPhail, M. K., N. F. Alley, E. M. Truswell and I. R. K. Sluiter (1994). "Early Tertiary vegetation: evidence from spores and pollen." History of the Australian Vegetation: Cretaceous to Recent. Ed. Robert S. Hill. Cambridge University Press. pp. 189–261. ISBN 0521401976. Partially available on Google Books.
- Manchester, S. R., Akhmetiev, M. A., & Kodrul, T. M. (2002). Leaves and fruits of Celtis aspera (Newberry) comb. nov. (Celtidaceae) from the Paleocene of North America and eastern Asia. International Journal of Plant Sciences, 163(5), 725-736.
- Stevens, P.F., Angiosperm Phylogeny Website: Cannabaceae
- "Celtis". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved February 12, 2012.
- Quattrocchi, Umberto (2000). CRC World Dictionary of Plant Names. I A–C. CRC Press. p. 468. ISBN 978-0-8493-2675-2.
- "GRIN Species Records of Celtis". Germplasm Resources Information Network. United States Department of Agriculture. Retrieved 2010-12-04.
- Ravikanthachari, Nitin (April 2018). "Larval host plants of the butterflies of the Western Ghats, India". Research Gate.
- Wahlberg, Niklas (October 2006). "Libythea myrrha Godart 1819". Tree of Life Web Project.
- Brower, Andrew V.Z. (2006). Problems with DNA barcodes for species delimitation: ‘ten species’ of Astraptes fulgerator reassessed (Lepidoptera: Hesperiidae). Systematics and Biodiversity 4(2): 127–132. doi: 10.1017/S147720000500191X PDF fulltext
- Hébert, Paul D.N.; Penton, Erin H.; Burns, John M.; Janzen, Daniel H. & Hallwachs, Winnie (2004). Ten species in one: DNA barcoding reveals cryptic species in the semitropical skipper butterfly Astraptes fulgerator. PNAS 101(41): 14812-14817. doi: 10.1073/pnas.0406166101 PDF fulltext Supporting Appendices
|Wikispecies has information related to Celtis|