Achnatherum is a genus of flowering grasses in the family Poaceae (order Poales), commonly known as needlegrasses. It comprises around 20 accepted species distributed across temperate Eurasia and North Africa, with the genus first formally described by the French botanist Palisot de Beauvois in 1812 in his Essai d'une Nouvelle Agrostographie.
The genus is closely related to Stipa and was long treated as part of that broadly defined genus; the two share tribe Stipeae and many morphological traits. Achnatherum can be distinguished by several characters: the young leaves are convolute (rolled inward lengthwise) rather than folded, the spikelets are laterally compressed, and the lemma carries spreading hairs up to 4 mm long near its base. The awn is either straight or gently curved but is never abruptly bent (geniculate) or twisted below the bend — features that characterise the typical awns of Stipa. The genus has also been treated under the synonym Lasiagrostis Link (1827) and the segregate Aristella Bertoloni (1834), both now regarded as heterotypic synonyms.
Taxonomic boundaries within tribe Stipeae have been revised repeatedly. During the 19th and 20th centuries, many species now placed in Achnatherum were variously assigned to Stipa, Agrostis, and Arundo. A major reorganisation in 2019 by Peterson and colleagues, based on molecular phylogenetic data, retained Achnatherum for the Eurasian lineage and moved the American needlegrass species into other reinstated or newly described genera.
Etymology
The name Achnatherum derives from the Greek achne (chaff or glume) and ather (awn or beard), referencing the awned lemmas that characterise the genus. The name was coined by Palisot de Beauvois in 1812 to distinguish these awned grasses from the then-allied genera Agrostis and Calamagrostis.
Distribution
Achnatherum is native to temperate regions of Eurasia and North Africa. The genus reaches from the Mediterranean and western Europe eastward across central Asia into Siberia and China, occupying dry grasslands, steppes, and rocky slopes within this range.
Taxonomy Notes
The genus has a complex nomenclatural history. It was first described by Palisot de Beauvois in 1812, but throughout the 19th and 20th centuries its species were scattered across Stipa, Agrostis, Arundo, Lasiagrostis, and Aristella. Modern molecular phylogenetic work, particularly Peterson et al. (2019), clarified the limits of tribe Stipeae and consolidated the Eurasian needlegrasses under Achnatherum, while transferring the formerly included American species to other genera. Plants of the World Online and World Flora Online recognise Aristella and Lasiagrostis as heterotypic synonyms.
