Allium dregeanum

Allium dregeanum is the sole known species of Allium endemic to sub-Saharan Africa.[1] It has also been described as the only Allium species endemic to the Southern Hemisphere,[2][3] though some descriptions of the genus also include Allium juncifolium (Chile) and Allium sellovianum (Brazil),[4][5] which are much less studied than Allium dregeanum. The distribution of Allium dregeanum extends from the summer-rainfall region, into the winter-rainfall zone of South Africa.[6] Since Allium species are almost exclusively found in the Northern Hemisphere, with major centers of diversity in Central Asia and western North America,[2] the biogeographical history of Allium dregeanum is of interest.

Allium dregeanum
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Amaryllidaceae
Subfamily: Allioideae
Genus: Allium
Species:
A. dregeanum
Binomial name
Allium dregeanum
Kunth

Though some theories have been put forward, no explanation for the geographic isolation of Allium dregeanum has been confirmed. In 1976, De Wilde-Dufyes proposed that Allium dregeanum is a modification of the European species Allium ampeloprasum, and may have been brought to South Africa by early European settlers.[6] De Saarker et al. contradicted this theory in 1997, when they explored genetic similarities between Allium dregeanum and Allium ampeloprasum, and did not find evidence of a significant genetic relationship. They also point to evidence that Allium dregeanum was already established in South Africa in the mid-17th century, when the first Dutch settlers colonized South Africa, but do not suggest other explanations for Allium dregeanum's isolation.[1]

Allium dregeanum occurs at elevations of 100-1000m, and flowers in spring and early summer (October to December).[6] It can grow to 0.6m by 0.2m, growing best in well-drained soils in sunny areas.[7] Allium dregeanum is also notable for its high chromosome counts: polyploidy is not uncommon in Allium, with 14% of representative Allium species exhibiting more than two sets of chromosomes,[8] but Allium dregeanum has particularly high ploidy levels, and can be octoploid or decaploid.[1]

References
  1. De Sarker, D.; Johnson, M.A.T.; Reynolds, A.; Brandham, P.E. (June 1997). "Cytology of the highly polyploid disjunct species, Allium dregeanum (Alliaceae), and of some Eurasian relatives". Botanical Journal of the Linnean Society. 124 (4): 361–373. doi:10.1006/bojl.1997.0109.
  2. Li, Qin-Qin; Zhou, Song-Dong; He, Xing-Jin; Yu, Yan; Zhang, Yu-Cheng; Wei, Xian-Qin (November 2010). "Phylogeny and biogeography of Allium (Amaryllidaceae: Allieae) based on nuclear ribosomal internal transcribed spacer and chloroplast rps16 sequences, focusing on the inclusion of species endemic to China". Annals of Botany. 106 (5): 709–733. doi:10.1093/aob/mcq177. PMC 2958792. PMID 20966186.
  3. Fay, Michael F.; Rudall, Paula J.; Chase, Mark W. (2006). "Molecular studies of subfamily Gilliesioideae (Alliaceae)". Aliso. 22: 367–371. doi:10.5642/aliso.20062201.30. Retrieved December 29, 2015.
  4. Block, Eric (2010). Garlic and Other Alliums. Cambridge, UK: The Royal Society of Chemistry. p. 12. ISBN 978-0-85404-190-9.
  5. El Shabrawy, Mona O.A.; Hosna, Hassnaa A.; El Garf, Ibrahim A.; Marzouk, Mona M.; Kawashty, Salwa A.; Saleh, Nabiel A.M. (October 2014). "Flavonoids from Allium myrianthum Boiss". Biochemical Systematics and Ecology. 56: 125–128. doi:10.1016/j.bse.2014.05.015.
  6. De Wilde-Duyfjes, Brigitta E.E. (1976). "A revision of the genus Allium L. (Liliaceae) in Africa". Mededelingen Landbouwhogeschool Wageningen. 76: 1–237.
  7. "Allium dregeanum". Plants for a Future. Retrieved December 30, 2015.
  8. Friesen, Nikolai; Fritsch, Reinhard M.; Blattner, Frank R. (January 2006). "Phylogeny and new intrageneric classification of Allium (Alliaceae) based on nuclear ribosomal DNA ITS sequences". Aliso. 22: 372–395. doi:10.5642/aliso.20062201.31.
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