Piptatherum is closely related to Oryzopsis Michaux and both are often merged, see for instance Clayton & Renvoize (1986) or Ryves & al. (1996). However, according to present-day taxonomists Oryzopsis is monospecific and restricted to North America (Mabberley 2008). The generic limits of Piptatherum proper are also under study. Romaschenko & al. (2011) demonstrated that section Miliacea (with two alien representatives in Belgium; see below) and section Virescentia (with the widespread species P. paradoxum (L.) Beauv. and P. virescens (Trin.) Boiss.) in fact should be excluded from Piptatherum s.str. The latter then would form a monophyletic assemblage with 22 core species in Eurasia. Hamasha & al. (2012) further explored generic limits in the group and proposed a new genus Oloptum to accommodate P. miliaceum (as O. miliaceum). This point of view was followed by e.g. Peterson & al. (2019). Pending further study Piptatherum is here maintained in its traditional sense.
Clayton W.D. & Renvoize S.A. (1986) Genera graminum. Grasses of the world. Kew Bull., Addit. Ser. 13: 390 p.
Freitag H. (1975) The genus Piptatherum (Gramineae) in Southwest Asia. Notes Roy. Bot. Gard. Edinb. 33: 341-408.
Freitag H. (1989) Piptatherum and Stipa (Gramineae) in the Arabian Peninsula and Tropical East Africa. In: Tan K. (ed.), The Davis and Hedge Festschrift: plant taxonomy, phytogeography and related subjects. Edinburgh, University Press : 115-132.
Hamasha H.R., von Hagen K.B. & Röser M. (2012) Stipa (Poaceae) and allies in the Old World: molecular phylogenetics realigns genus circumscription and gives evidence on the origin of American and Australian lineages. Plant Syst Evol 298: 351-367.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
Peterson P.M., Romaschenko K., Soreng R.J. & Reyna J.V. (2019) A key to the North American genera of Stipeae (Poaceae, Pooideae) with descriptions and taxonomic names for species of Eriocoma, Neotrinia, Oloptum, and five new genera: Barkworthia, ×Eriosella, Pseudoeriocoma, Ptilagrostiella, and Thorneochloa. PhytoKeys 126: 89–125. [available online at: https://phytokeys.pensoft.net/article/34096/]
Romaschenko K., Peterson P.M., Soreng R.J., Futorna O. & Susanna A. (2011) Phylogenetics of Piptatherum s.l. (Poaceae: Stipeae): evidence for a new genus, Piptatheropsis, and resurrection of Patis. Taxon 60(6): 1703-1716.
Ryves T.B., Clement E.J. & Foster M.C. (1996) Alien grasses of the British Isles. BSBI, London: XX + 181 p.
Tutin T.G. (1980) Piptatherum. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 5. Cambridge University Press, Cambridge: 246-247.