Taxonomic revision of the genus Amaranthus (Amaranthaceae) in Saudi Arabia Author Hassan, Walaa A. Author Al-Shaye, Najla A. 0000-0002-0447-8613 Department of Biology, College of Science, Princess Nourah bint Abdulrahman University, P. O. Box 84428, Riyadh 11671, Saudi Arabia & naaalshaye @ pnu. edu. sa; https: // orcid. org / 0000 - 0002 - 0447 - 8613 naaalshaye@pnu.edu.sa Author Alghamdi, Salma 0000-0001-7716-2233 Department of Biology, College of Science, Princess Nourah bint Abdulrahman University, P. O. Box 84428, Riyadh 11671, Saudi Arabia & saatalghamdi @ pnu. edu. sa; https: // orcid. org / 0000 - 0001 - 7716 - 2233 saatalghamdi@pnu.edu.sa Author Korany, Shereen M. 0000-0002-9355-3952 Department of Biology, College of Science, Princess Nourah bint Abdulrahman University, P. O. Box 84428, Riyadh 11671, Saudi Arabia & smkorany @ pnu. edu. as; https: // orcid. org / 0000 - 0002 - 9355 - 3952 smkorany@pnu.edu.as Author Iamonico, Duilio 0000-0001-5491-7568 Ce. R. S. I. Te. S., University of Rome Sapienza, viale XXIV Maggio 7, 04100 - Latina, Italy & duilio. iamonico @ uniroma 1. it; https: // orcid. org / 0000 - 0001 - 5491 - 7568 & Authors that contributed equally to the work text Phytotaxa 2022 2022-12-20 576 2 135 157 http://dx.doi.org/10.11646/phytotaxa.576.2.1 journal article 53324 10.11646/phytotaxa.576.2.1 1a9bd59f-7293-432f-b3c1-6df0bc659474 1179-3163 7461280 5. Amaranthus graecizans L. , Sp. Pl. 2: 990. 1753 Type ( lectotype designated by Fernald 1945: 139 ):— U.S.A. Habitat in Virginia , Herb. Clayton No. 442 (BM000051563!, image of the lectotype available at https://data.nhm.ac.uk/object/ca635ca9-9252-42a3-9082-60ec097bc2d6/1641427200000). = Amaranthus angustifolius Lam., Encycl. [J. Lamarck & al.] 1: 115. 1783, nom. illeg. Art. 52.21 of the ICN ( Turland et al. 2018 ). 1 Amaranthus angustifolius was described citing among synonyms an earlier legitimate name ( A. graecizans L.). Description:— Herbs 1–8 dm tall, monoecious, annual (therophyte). Stems erect or ascending, ± glabrous (sometimes sparsely pubescent in the distal region), pale to black-brown to reddish, usually branched. Leaves usually green, ovaterhomboidal to lanceolate (decreasing in size towards stem apex), with entire margins, apex acute or obtuse, sometimes mucronate, base cuneate, glabrous, petioled [petiole (1.0–)2.0–5.0(–6.0) cm long]. Synflorescences arranged in axillary glomerules, often reddish. Floral bracts brown-yellowish, lanceolate (1.2–2.0 × 0.3–0.6 mm ) as long as or shorter than the perianth, acute, margin entire, glabrous. Staminate flowers with 3 tepals, ovate to lanceolate; stamens 3. Pistillate flowers with 3 tepals, ovate-lanceolate [(1.3–)1.5–2.0 × 0.4–0.7 mm ], with acute, and often mucronate apex; stigmas 3. Fruit brown, subglobose [(1.5–)2.0–2.5(–2.7) × (1.0–)1.4–1.5(–1.8) mm], longer than the perianth, rugose, dehiscent. Seed lenticular [1.0–1.3(–1.5) mm in diameter], black to dark-brown. Chorology:— Paleotemperate taxon native to Europe, Central-Western Asia, and Northern Africa ( Carretero 1990 , Akeroyd 1993 , Boulos 1999, Ghafoor et al. 1977 , Fennane & Tatou 2005 , Le Floc’h et al. 2008), it is considered introduced in some European countries, North America, South Africa , and Australia ( POWO 2022a and literature therein). Concerning Saudi Arabia , it is native. At subspecific rank two main distribution areas can be distinguished, the first one including Central and southern Europe plus North Africa [ subsp. graecizans and subsp. sylvestris (Vill.) Brenan ], the second area being the eastern Europe ( Russia and adjacent territories) plus Central and southern Asia [ subsp. aschersonianus (Thell.) Costea and subsp. thellungianus (Nevski) Gusev ] (see Iamonico 2015: 34). Occurrence in Saudi Arabia :— See varieties. Taxonomic annotations:— Amaranthus graecizans is a species morphologically variable, especially regarding the hairiness of stem, the shape of leaves (lanceolate or ovate-rhomboidal), the structure of synflorescence (with or without terminal synflorescence), the apex of bracts and tepals (acute-mucronate or awned), the margin of seed (obtuse or acute), and the dehiscence/indehiscence of fruit. These variability is currently interpreted recognizing four subspecies, i.e. subsp. graecizans , subsp. sylvestris , subsp. aschersonianus , subsp. thellungianus (see e.g., Costea 2003 ). Based on our field surveys and according to Chaudhary (1998) three subspecies occur in Saudi Arabia . These taxa can be distinguisced as follow: 1. Bracts and tepals awned (awn 0.3–0.7 mm long)................................................................................................ subsp. thellungianus 2. Bracts and tepals mucronate (mucro about 0.1 mm long)..................................................................................................................3 3. Leaf blade lanceolate [2.0–3.0(–4.0) × 0.5–1.0 cm], ratio length/width of the blade 3.0–6.0................................ subsp. graecizans - Leaf blade ovate-rhomboidal [5.0–6.0 × 2.5–3.0(–3.5) cm], ratio length/width of the blade 1.8–2.2....................... subsp. sylvestris