Echinochloa muricata var. wiegandii (Fassett) Mohlenbr., Ill. Fl. Illinois (ed. 2) 396. 2001.

Hoste, Ivan & Verloove, Filip, 2022, Taxonomy of the weed species of the genus Echinochloa (Poaceae, Paniceae) in Southwestern Europe: Exploring the confused current state of affairs, PhytoKeys 197, pp. 1-31 : 1

Echinochloa muricata var. wiegandii (Fassett) Mohlenbr., Ill. Fl. Illinois (ed. 2) 396. 2001.

Basionym.

Echinochloa pungens (Poir.) Rydb. var. wiegandii Fassett, Rhodora 51(601): 2. 1949.

Type.

USA: Oregon, Hayden Island , sandy roadside, J.C. Nelson 1974, 8 Sep 1915 (holotype GH). Image available at https://kiki.huh.harvard.edu/databases/specimen_search.php?mode=details&id=126740 .

Remarks on E. muricata .

Echinochloa muricata is native to North America. Its status as separate from E. crus-galli , which was inadvertently introduced there long ago from Europe, was contested by Hitchcock (1920, 1935, 1950). Hitchcock (1920) rejected the separate status stating that he was unable to distinguish the two species based on the distinguishing features given by Fernald (1915). However, further studies by Wiegand (1921) and especially by Fassett (1949) confirmed the separate status of E. muricata ( Gould et al. 1972). Probably, largely due to Hitchcock’s influential publications, a significant share of American authors have for decades combined native and introduced taxa under E. crus-galli in floras and weed-control publications ( Maun and Barrett 1986). In the 21st century, some researchers still refer to New World E. crus-galli - not to be confused with E. crus-galli introduced in North America from Europe - rather than using the name E. muricata ( Aoki and Yamaguchi 2008). By now, however, molecular research has confirmed E. muricata as a separate species, clearly distinct from E. crus-galli ( Claerhout et al. 2016; Mascanzoni 2018). This should put an end to the confusion that goes back to the days of Linnaeus, as it has been demonstrated that the type specimen of E. crus-galli in fact belongs to E. muricata ( Crespo et al. 2020a).

Echinochloa muricata is a highly variable species, though less so than E. crus-galli . This, combined with its resemblance to E. crus-galli , has added to the difficulty for agronomists and botanists on both sides of the Atlantic to detect and correctly name its introduced populations. Early records of introduced E. muricata from France revealed morphologically very uniform populations (as E. pungens [Poir.] Rydb. var. Echinochloa pungens microstachya [Wiegand] Fernald & Griscom; Deschatres et al. 1974). This resulted in identification keys that made it harder to correctly identify clearly deviating forms of E. muricata that had established in maize fields in Belgium ( Hoste 2004).

The European populations of E. muricata exhibit only part of the variation found in the natural range of the species. So far, three morphologically distinct varieties have been recorded from Belgium and France. Echinochloa muricata var. muricata , with larger spikelets, seems to occur only as an ephemeral alien ( Hoste 2004). References to this variety in France require confirmation as they are probably based on misidentifications ( Jauzein 1995; Tison and de Foucault 2014). The specimens with smaller spikelets recorded from Belgium are of two clearly different types, apparently with very few intermediates. The characteristics given in the key are mainly based on observations on European-origin plants. Specimens with unawned spikelets with strongly spreading bristles are assigned to var. Echinochloa muricata microstachya Wiegand, and those with shortly awned spikelets with more appressed bristles to var. Echinochloa muricata wiegandii (Fassett) Mohlenbr.; see Hoste (2004) and Bomble (2016) for illustrations of the inflorescences and spikelets. Genetic research on specimens collected from maize fields in Belgium has resulted in two clusters of E. muricata collections ( Claerhout et al. 2016). From the study of the morphological features of three of these collections, we tentatively conclude that the two clusters C and D identified by Claerhout et al. (2016) correspond to var. Echinochloa muricata wiegandii and var. Echinochloa muricata microstachya , respectively (IH, unpublished data). Nonetheless, more genetic studies are needed to confirm whether the three morphologically distinct varieties are indeed genetically well-defined taxa. Both within and outside North America, forms of E. muricata with smaller spikelets have shown a stronger tendency to spread as weeds outside their natural range ( Dore and McNeill 1980; Michael 2001).

Echinochloa muricata is a species of moist, disturbed sites. It is not an important weed of rice fields ( Michael 2001, 2003) and in Europe it mainly occurs as a weed in maize fields ( Hoste 2004; Bomble 2016).