Amaranthus quitensis Kunth

Raus, Thomas, 2022, Taxonomic, nomenclatural and floristic review of Amaranthaceae of Greece and neighbouring countries, Willdenowia 52 (3), pp. 335-357 : 346

18. Amaranthus quitensis Kunth in Humboldt & al., Nov. Gen. Sp. 2, ed. folio: 156; ed. quarto: 194. 1818 ≡ Amaranthus hybridus var. quitensis (Kunth) Covas in Darwiniana 5: 336. 1941 ≡ Amaranthus retroflexus subsp. quitensis (Kunth) O. Bolòs & Vigo in Butl. Inst. Catalana Hist. Nat., Secc. Bot. 38: 89. 1974 ≡ Amaranthus hybridus subsp. quitensis (Kunth) Costea & Carretero in Sida 19: 955. 2001. – Holotype: South America, Ecuador, in ripa fluvii Guallabambae, alt. 1030 hex. [= 1850 m] (Regno Quitensi), Jun 1802, Humboldt & Bonpland 3082 (P P00136030). – “ Amaranthus caudatus ” sensu Greuter & al. (1984:

46), pro parte [non Amaranthus caudatus L., Sp. Pl.:

990. 1753].

Remarks — This species is native to subtropical and temperate South America, from Ecuador and S Brazil to S Argentina (Patagonia); it is introduced as a casual weed in Canada and in parts of W, C and N Europe ( Hügin 1986, 1987; Karlsson 2001; Hand & al. 2022), where it is mostly ephemeral due to lack of frost resistance. Amaranthus quitensis is a river-bank pioneer in its native range and the supposed wild ancestor of A. caudatus . It is naturalized in the Azores and Balearic Islands ( Bayón 2015: 286) and in Greece ( Raus 1997; Iamonico 2015a); localities of collect- ed specimens are known from all over Greece except the North Aegean islands. The flowering and fruiting period of A. quitensis extends to about seven months in Greece, from early summer to late autumn, which may be one reason for its rapid spread and naturalization ( Arianoutsou & al. 2010). The species is clearly distant and chiefly distinguished from A. hybridus by the obovate to narrowly spathulate, apically obtuse inner perianth segments of the female flowers and by the usually numerous patent, pale brownish green, often sausage-shaped, apically obtuse lateral inflorescence branches, a diagnostic feature that is explicitly corroborated by Karlsson (2001: 60, fig. 25). A photograph in Vangjeli (2017: 120, under A. hybridus ) shows exactly these characters and may be interpreted as the first record of A. quitensis for Albania. In A. hybridus , on the contrary, all perianth segments are acute or acuminate, and the lateral inflorescence branches are erectopatent and thinning toward the apex. More similar is A. retroflexus on the basis of its obtuse to truncate-emarginate perianth segments of the female flowers, but that species differs in its markedly pubescent stem indumentum and few, erect, stout, usually pale to silvery green inflorescence branches usually appressed to the main axis (not brownish green and horizontally patent as in A. quitensis ). The two taxa are likewise appropriately treated as separate species in accordance with Aellen (1959), Hügin (1987), Raus (1997), Karlsson (2001) and Iamonico (2015a). Unfortunately, A. quitensis fell into early oblivion, only c. 30 years after its publication as a species new to science, when Moquin-Tandon (1849: 265) categorized it as an insufficiently known taxon (“species non satis nota”) by misjudgement of its bract characters (“calyce bracteis duplo longiore” instead of “bracteis subulatis, calyce duplo longioribus” as correctly stated in the protologue by Kunth in Humboldt & al. 1818). This is the reason why A. quitensis is not treated in any of the classical basic floras covering Greece (see Table 1) and adjacent countries ( Iamonico 2015a). Its rehabilitation as an accepted species happened only in the early 20 th century ( Zobel 1909; Höck 1910; Thellung 1912; Zimmermann 1913) on the basis of correctly determined specimens of adventive casuals in C and S Europe. The name was reintroduced into current use by Thellung (1914), Aellen (1959), Soó (1980: 460), Hügin (1987), Raus (1997, see Table 1) and Pedersen (1999). There is, however, much disagreement among flora-writers on the taxonomic rank of A. quitensis and A. hybridus (summarized in Bayón 2015: 284–285), and it seems floristically rather unhelpful to again hide away the former in the latter, either as a plain synonym ( Coons 1977) or at any infraspecific rank ( Covas 1941; Costea & al. 2001a; Bayón 2015). Amaranthus quitensis may yet also be found in Albania (see above), Bulgaria and North Macedonia, where to date it simply has not been keyed out and distinguished from A. hybridus .