Diagnostic key for genera of Amaranthaceae s.str. occurring in Saudi Arabia 1. Leaves alternate..................................................................................................................................................................................2 2. Flowers unisexual...............................................................................................................................................................................3 3. Each fertile flower subtended by two modified sterile flowers...................................................... Digera muricata subsp. muricata 3. Fertile flower never subtended by modified sterile flowers............................................................................................. Amaranthus 2. Flowers hermaphrodite.......................................................................................................................................................................4 4. Fruit including one seed; stigma 1, capitate .......................................................................................................................................5 5. Annual herb; tepals 1.00− 1.25 mm long ......................................................................................................... Nothosaerva brachiata 5. Perennial herb; tepals 3.25−4.00 mm long................................................................................................................... Saltia papposa 4. Fruit including 2 or more seeds; stigmas 2−3, linear .............................................................................................................. Celosia 1. Leaves opposite ..................................................................................................................................................................................6 6. Synflorescence in axillary glomerules and/or terminal heads (no terminal spike- or panicle-structures) .........................................7 7. Stigma 1, capitate .......................................................................................................................................................... Alternanthera 7. Stigmas 2, linear .................................................................................................................................................. Gomphrena globosa 6. Synflorescence in terminal spike- or panicle-structures and/or terminal heads.................................................................................8 8. Sterile flowers present ......................................................................................................................... Pupalia lappacea var. velutina 8. Sterile flowers absent .........................................................................................................................................................................9 9. Synflorescence in terminal heads; pseudostaminoids absent ................................................................ Psilotrichum gnaphalobryum 9. Synflorescence in terminal spike-structures; pseudostaminoids present..........................................................................................10 10. Stigmas 2, linear ......................................................................................................................................................................... Aerva 10. Stigma 1, capitate .............................................................................................................................................................................11 11. Pseudostaminoids not fringed................................................................................................................ Psilotrichum gnaphalobryum 11. Pseudostaminoids fringed................................................................................................................................................. Achyranthes

Published as part of Hassan, Walaa A., Al-Shaye, Najla A. & Iamonico, Duilio, 2023, A critical inventory of the family Amaranthaceae s. str. in Saudi Arabia, pp. 223-246 in Phytotaxa 626 (4) on page 227, DOI: 10.11646/phytotaxa.626.4.1, http://zenodo.org/record/10212988