Amaranthus blitoides S. Watson

Raus, Thomas, 2022, Taxonomic, nomenclatural and floristic review of Amaranthaceae of Greece and neighbouring countries, Willdenowia 52 (3), pp. 335-357 : 337-338

3. Amaranthus blitoides S. Watson in Proc. Amer. Acad. Arts 12: 273. 1877. – Lectotype (designated by Fernald 1945: 139): North America, U.S.A., Iowa, Ames , gravelly or sandy soils especially around buildings and along roads, Bessey (GH GH00036983 ).

Remarks — Amaranthus blitoides is native to C North America ( U.S.A.: Michigan to Texas, see Mosyakin & Robertson 2003); it is introduced and naturalized elsewhere in North and South America, Africa and temperate Eurasia ( Jalas & Suominen 1980: 94; Bayón 2015: 306). The species is occasionally considered invasive as a strong competitor causing threats in cultivated fields by loss of crop yield, or decreasing the floristic richness of ecosystems by forming cohesive stands (see, e.g., Iamonico 2015b). It was first recorded in Greece in 1917 (see Table 1). The flowering and fruiting period of A. blitoides may extend to about eight months in Greece, which may be one reason for its successful spread and naturalization ( Strid & Tan 1997: map 266; Arianoutsou & al. 2010); regular winter-flowering has been observed in December and January ( Gilli 1977; Raus 1994). Naturalized also in Albania, North Macedonia, Bulgaria and Turkey ( Iamonico 2015a), the species is ranked among the most widespread alien vascular plants in Europe ( Pyšek & al. 2009: 50, t. 4.3).

Greek material is represented by two varieties, the widespread Amaranthus blitoides var. blitoides and the more scattered A. blitoides var. reverchonii Uline & W. L. Bray. Both varieties are scarcely discernible in autumnal plants with habitat-induced very small and dense, spirally arranged foliage (leaf blades 0.6–1.0 cm long), referred to as A. blitoides var. thellungii (Sennen ex Thell.) Thell. or A. blitoides var. densifolius Uline & W. L. Bray in literature ( Uline & Bray 1894; Sennen 1912).

They merit at most the taxonomic rank of form, which is proposed here. The shape of the leaf blade is usually obovate to elliptic-spathulate and 1.5–2 times as long as wide in Amaranthus blitoides f. thellungii vs oblong-lanceolate and at least 2.5 times as long as wide in A. blitoides f. densifolius ( Thellung 1914: 292; and pers. obs.).

1. Leaf blade usually uniformly green, obovate to elliptic-spathulate, 1.5–2 times as long as wide, apex obtuse......... Amaranthus blitoides var. blitoides

– Leaf blade narrower, often white-speckled, oblonglanceolate, at least 2.5 times as long as wide, apex acute...... Amaranthus blitoides var. reverchonii