Amaranthus

Amaranthus L.

Amaranthus is a genus of ca. 70 species, mostly confined to the tropics, subtropics and warm-temperate regions of the world. Several species nowadays have an almost worldwide distribution as agricultural weeds. Few species are cultivated as ornamentals (see for instance Jäger & al. 2008) or as pseudocereals. No species are native in Belgium although Amaranthus blitum is sometimes claimed as an archaeophyte.

A very useful worldwide revision for the monoecious species from subgenera Albersia and Amaranthus was recently published (Bayón 2015).

Amaranthus is a fairly difficult genus and species delimitation is often controversial. In recent times species concepts and interspecific relationships have considerably changed, especially within the Amaranthus hybridus species complex. We here follow Costea & al. (2001). This treatment deviates from that applied in the current edition of the Flora of Belgium (Lambinon & al. 2004); see table of concordance here under.

Lambinon & al. (2004)

Current treatment

Amaranthus blitum subsp. blitum var. oleraceus

A. blitum subsp. oleraceus

A. hybridus subsp. bouchonii

A. powellii subsp. bouchonii

A. hybridus subsp. cruentus

A. cruentus

A. hybridus subsp. hybridus var. pseudoretroflexus

A. powellii subsp. powellii

A. hybridus subsp. hybridus var. erythrostachys

A. hypochondriacus

A. quitensis

A. hybridus subsp. quitensis

A. rudis

A. tuberculatus var. rudis

A. tuberculatus

A. tuberculatus var. tuberculatus

Hybridisation often occurs in the genus Amaranthus, especially within the Amaranthus hybridus complex. At least two hybrids have been recorded in Belgium: Amaranthus hybridus subsp. hybridus x A. retroflexus (A. xozanonii Priszter) and A. powellii subsp. bouchonii x A. retroflexus (A. xralletii Contré, A. x ozanonii Priszter nothosubsp. ralletii (Contré) Lambinon) (Saintenoy-Simon 1986, Meerts (1986). Both nothotaxa are partly sterile, have intermediate tepals of female flowers and often exhibit a very dense, contracted inflorescence. They are poorly known and possibly more often produced than generally admitted.

1. Plant dioecious. Inflorescence always terminal === 2

1. Plant monoecious. Inflorescence terminal or axillary === 5

2. Plant female === 3

2. Plant male === 4

3. Tepals 5, all well developed (the outer longest). Bracts 4-6 mm long, longer than the tepals === 12. Amaranthus palmeri p.p.

3. Tepals 1-2. Bracts ca. 2 mm long, shorter than longest (outer) tepal === 18. A. tuberculatus p.p.

4. Bracts ca. 4-5 mm long, longer than the outer tepals === 12. A. palmeri p.p.

4. Bracts ca. 2 mm long, shorter than longest (outer) tepal ==== 18. A. tuberculatus p.p.

5. Spines present in the leaf axils. Utricle indehiscent or irregularly dehiscent ===        15. A. spinosus

5. Spines absent in the leaf axils. Utricle dehiscent or not === 6

6. Female flowers with (4-) 5 tepals === 7

6. Female flowers with 3 tepals === 20

7. All flowers in clusters in leaf axils === 8

7. Flowers in terminal, leafless, spike-like inflorescences (often also some clusters in leaf axils) === 11

8. Tepals of female flowers clawed at base, conspicuously spathulate at apex, curved outwards at maturity. Utricle indehiscent === 16. A. standleyanus p.p.

8. Tepals of female flowers linear-lanceolate, not or only slightly spathulate at apex, erect. Utricle dehiscent or not === 9

9. Leaves small, rhombic, less than 20 mm long, strongly undulate at margin === 5. A. crispus

9. Leaves not strongly undulate at margin, often longer === 10

10. Utricle dehiscent. Tepals of female flowers always 4-5. Leaves not distinctly notched at apex === 2. A. blitoides

10. Utricle indehiscent. Tepals of female flowers usually 3, rarely 5 in some flowers. Leaves distinctly notched at apex === 3. A. blitum p.p.

11. Bracts of female flowers inconspicuous, shorter than the tepals. Utricle indehiscent === 12

11. Bracts of female flowers as long as to longer than the tepals, often needle-like. Utricle dehiscent or rarely indehiscent === 14

12. Perennial. Leaves linear to narrowly lanceolate, at most 10 mm wide === 11. A. muricatus

12. Annual. Leaves usually wider, never linear to narrowly lanceolate === 13

13. Tepals of female flowers usually 3, rarely 5 in some flowers, never clawed, nor spathulate or bent outwards at maturity. Leaves distinctly notched at apex === 3. A. blitum p.p.

13. Tepals of female flowers 5, clawed at base, conspicuously spathulate at apex, bent outwards at maturity === 16. A. standleyanus p.p.

14. Tepals of female flowers spathulate at apex === 15

14. Tepals of female flowers linear-lanceolate === 17

15. Inflorescence red or yellow, pendent at maturity. Bracts not exceeding stigma branches. Tepals not exceeding utricle === 4. A. caudatus

15. Inflorescence green. Bracts longer than stigma branches. Tepals longer than utricle === 16

16. Stem sparsely hairy below inflorescence. Inflorescence with many lateral, patent, thin branches. Tepal midrib extending beyond apex into mucro === 9. A. hybridus p.p. (subsp. quitensis)

16. Stem densely hairy below inflorescence. Inflorescence with short, thick, ascendent or erect branches. Tepal midrib ending below apex === 14. A. retroflexus

17. Inflorescence red or purple === 18

17. Inflorescence green === 19

18. Utricle abruptly narrowed towards apex. Stigma branches parallel, erect. Inflorescence usually with many lateral, thin, patent or ascending branches. Bracts usually not exceeding stigma branches === 6. A. cruentus

18. Utricle gradually narrowed towards apex. Stigma branches divergent. Inflorescence usually stiff, with thick, erect or ascending branches. Bracts up to twice as long as stigma branches === 10. A. hypochondriacus

19. Bracts 2-4 mm long. Inflorescence usually soft and lax with spreading branches. Utricle dehiscent === 9. A. hybridus p.p. (subsp. hybridus)

19. Bracts 4-7 mm long. Inflorescence usually erect with stiff branches === 13. A. powellii (incl. subsp. bouchonii)

20. Leaves distinctly notched at apex === 3. A. blitum p.p.

20. Leaves not notched at apex === 21

21. All flowers in clusters in leaf axils. Utricle dehiscent === 22

21. Flowers in terminal, leafless, spike-like inflorescences (often also some clusters in leaf axils) === 24

22. Tepals of female flowers long-acuminate at apex, awns usually reflexed outwards === 17. A. thunbergii

22. Tepals of female flowers acute to short-acuminate, not reflexed outwards === 23

23. Bracts stiff and pungent, ca. 2x as long as tepals of female flowers === 1. A. albus

23. Bracts not stiff and pungent, at most slightly longer than tepals of female flowers === 8. A. graecizans

24. Perennial. Stem hairy in upper part (below inflorescence). Utricle inflated, smooth. Inflorescence branches thick === 7. A. deflexus

24. Annual. Stem (sub-) glabrous in upper part. Utricle not inflated, distinctly wrinkled. Inflorescence branches thin and slender === 19. A. viridis

Additional aliens: Amaranthus acutilobus Uline et Bray (N-Am., wool alien), A. capensis Thell. subsp. capensis (S-Afr., wool alien), A. capensis subsp. uncinatus (Thell.) Brenan (syn.: A. dinteri Schinz subsp. uncinatus Thell.) (S-Afr., wool alien), A. clementii Domin (syn.: A. pallidiflorus F. Muell. var. viridiflorus Thell.) (Aus., wool alien), A. macrocarpus Benth. var. macrocarpus (Aus., wool alien), A. macrocarpus Benth. var. pallidus Benth. (Aus., wool alien), A. mitchellii Benth. (Aus., wool alien), A. polygonoides L. (C- and S-Am., wool alien) and A. scleropoides Uline et Bray (N-Am., wool alien).

 


Literature:

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Aellen P. (1959) Amaranthus. In: Hegi G. (ed.), Illustrierte Flora van Mitteleuropa, vol. 3(2) (2nd ed.). Carl Hanser Verlag, München: 465-516.

Aellen P. (1964) Amaranthus. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 1. Cambridge University Press, Cambridge: 109-110.

Bayón N.D. (2015)Revisión Taxonómica de las Especies Monoicas de Amaranthus (Amaranthaceae): Amaranthus subg. Amaranthus y Amaranthus subg. Albersia. Annals Missouri Bot. Gard. 101(2): 261-383. [available online at: http://www.bioone.org/doi/pdf/10.3417/2010080]

Brenan J.P.M. (1981) The genus Amaranthus in Southern Africa. J. S. African Bot. 47: 451-492.

Carretero J.L. (1990) Amaranthus. In: Castroviejo S. & al. (eds.), Flora Iberica, vol. 2. Real Jardín Botánico, Madrid: 554-569.

Costea M. (1997a) The genus Amaranthus L. section Amaranthus in Romania. Acta Horti Buc. 1995-1996: 105-120.

Costea M., Sanders A. & Waines G. (2001a) Preliminary results towards a revision of the Amaranthus hybridus species complex (Amaranthaceae). Sida 19(4): 931-974.

Costea M., Sanders A. & Waines G. (2001b) Notes on some little known Amaranthus taxa (Amaranthaceae) in the United States. Sida 19(4): 975-992.

Costea M. & Tardif F.J. (2003) Conspectus and notes on the genus Amaranthus in Canada. Rhodora 105: 260-281.

Duvigneaud J. & Lambinon J. (1976) Quelques Amaranthus intéressants ou nouveaux pour la flore belge. Dumortiera 2: 27-32.

Frey A. (1974) Rodzaj Amaranthus L. w Polsce. Fragmenta Florist. Geobot. 20(2): 143-201.

Hügin G. (1986) Die Verbreitung von Amaranthus-Arten in der südlichen und mittleren Oberrheinebene sowie einigen angrenzenden Gebieten. Phytocoenologia 14: 289-379.

Hügin G. (1987) Einige Bemerkungen zu wenig bekannten Amaranthus-Sippen (Amaranthaceae) Mitteleuropas. Willdenowia 16: 453-478.

Iamonico D. (2015) Taxonomic revision of the genus Amaranthus (Amaranthaceae) in Italy. Phytotaxa 199(1): 1-84.

Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.

Kloos A.W. Jr. (1949) Dix espèces d’Amaranthus nouvelles pour la flore belge. Bull. Jard. Bot. Etat Brux. 19: 243-250.

Lambinon J. (1963) Contribution à l’étude de la flore adventice de la Belgique. III. Une amarante dioique nouvelle pour la Belgique: Amaranthus palmeri S. Wats. Lejeunia N.S. 18: 1-3.

Meerts P. (1986) A propos d’Amaranthus x ralletii. Dumortiera 36: 26-27.

Mosyakin S.L. & Robertson K.R. (2003) Amaranthus. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 4. Oxford University Press, New York-Oxford: 410-435.

Saintenoy-Simon J. (1986) Présence en Belgique d’Amaranthus x ralleti (sic). Dumortiera 34-35: 146.

Sauer J.D. (1955) Revision of the dioecious amaranths. Madroño 13: 5-46.

Sauer J.D. (1967) The grain amaranths and their relatives: a revised taxonomic and geographic survey. Ann. Missouri Bot. Gard. 54: 103-137.

Schnedler W. (1978) Pflanzen, von denen in der Mitteleuropäischen Literatur selten oder gar keine Abbildungen zu finden sind. Folge VI. Amaranthus-Arten I. Gött. Flor. Rundbr. 12: 3-14.

Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.

Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith