Diplachne Beauv.
Considerable controversy has surrounded the generic placement of Leptochloa and its closest relatives. For quite a long time Diplachne and Leptochloa were both given generic rank. Cladistic studies recently had rejected the recognition of the segregate genus Diplachne (Snow 1998) and, as a consequence, all taxa formerly placed in Diplachne were transferred to Leptochloa (see also Verloove & Lambinon 2006). As such, Leptochloa included ca. 32 species that are native in warm-temperate and subtropical regions of the world. However, more recent molecular phylogenetic studies demonstrated that Leptochloa s.l. was polyphyletic and shed a new light on the generic boundaries within this group (Peterson & al. 2012; see also Snow & Peterson 2012, Peterson & al. 2015). These studies support the dissolution of Leptochloa s.l. into five genera: Dinebra (with 23 species), Diplachne (two species), Disakisperma (four species; Snow & al. 2013), Leptochloa s.str. (five species) and Trigonochloa (two species). A taxonomic revision of Diplachne in its current, restricted sense was published by Snow & al. (2018). None of the species is native in Belgium but several were formerly recorded as wool aliens in the valley of river Vesdre near Verviers. Belgian representatives are now classified as follows:
Dinebra decipiens (R. Brown) P.M. Peterson & N. Snow subsp. decipiens (syn.: Leptochloa decipiens (R. Brown) Stapf ex Maiden s.l. (incl. L. ciliolata (Jedwabn.) S.T. Blake)) (Aus., wool alien);
Dinebra decipiens var. peacockii (Maiden & Betche) P.M. Peterson & N. Snow (syn.: D. decipiens (R. Brown) P.M. Peterson & N. Snow subsp. peacockii (Maiden et Betche) P.M. Peterson & N. Snow, Leptochloa peacockii (Maiden et Betche) Domin, Diplachne peacockii Maiden et Betche, L. decipiens subsp. peacockii (Maiden et Betche) N. Snow) (Aus., wool alien);
Dinebra divaricatissima (S.T. Blake) P.M. Peterson & N. Snow (syn.: Leptochloa divaricatissima S.T. Blake) (Aus., wool alien);
Dinebra panicea (Retz.) P.M. Peterson & N. Snow var. brachiata (Steud.) P.M. Peterson & N. Snow (syn.: D. panicea subsp. brachiata (Steud.) P.M. Peterson & N. Snow, Leptochloa panicea (Retz.) Ohwi subsp. brachiata (Steud.) N. Snow, L. brachiata Steud., L. filiformis (Lam.) Beauv.) (Am., wool alien);
Dinebra retroflexa (Vahl) Panzer (Afr., As., wool alien);
Diplachne fusca (L.) P. Beauv. ex. Roemer. et Schult. subsp. fascicularis (Lam.) P.M. Peterson & N. Snow (syn.: Diplachne fascicularis (Lam.) Beauv.) (Am., grain and wool alien);
Diplachne fusca (L.) P. Beauv. ex. Roemer. et Schult. subsp. fusca (syn.: Leptochloa fusca (L.) Kunth, D. malabarica (L.) Merr.; incl. Leptochloa parviflora (R. Brown) Verloove et Lambinon, syn.: Diplachne parviflora (R. Brown) Benth.)) (trop., wool alien);
Diplachne fusca (L.) P. Beauv. ex. Roemer. et Schult. subsp. uninervia (J. Presl) P.M. Peterson & N. Snow (syn.: Diplachne uninervia (J. Presl) Parodi, Leptochloa uninervia (J. Presl) Hitchc. et Chase, L. fusca (L.) Kunth subsp. uninervia (J. Presl) N. Snow) (Am., grain and wool alien);
Disakisperma dubia (Kunth) P.M. Peterson & N. Snow (syn.: Leptochloa dubia (Kunth) Nees) (Am., wool alien).
Out of these two taxa of Diplachne (Diplachne fusca subsp. uninervia and D. fusca subsp. fascicularis) and Dinebra retroflexa have been recorded in Belgium in recent years.
In general appearance Diplachne is often very reminiscent of a tall species of Eragrostis. Both genera are easily distinguished by their ligules: these are membranous in Diplachne but ciliolate in Eragrostis.
Several species of Leptochloa s.l. are of economic importance: some are cultivated as minor cereals or for fodder (Mabberley 2008) and a few are noxious environmental and/or agricultural weeds.
1. Uppermost leaf blades often exceeding the panicles, panicles usually partially enclosed in the uppermost leaf sheaths. Lemma pale at maturity, usually smoky white, mucronate to awned === subsp. fascicularis
1. Uppermost leaf blades exceeded by the panicles, panicles usually completely exserted. Lemma darker at maturity, usually lead-colored, truncate to mucronate (not awned) === subsp. uninervia
References
Brummitt R.K. (1978) Report of the Committee for Spermatophyta 20: Proposal 415. 307 Leptochloa Beauvois (1812) (Gramineae) vs Rabdochloa Beauvois (1812). Taxon 27 (2/3): 285-289.
Cámara Hernández J. (2001) Morfología de las Inflorescencias de Diplachne y Leptochloa (Poaceae). Bol. Soc. Argent. Bot. 36(3-4): 267-278.
Lambinon J. (1959) Contribution à l’étude de la flore adventice de la Belgique. II. Etude surdiverses Gramineae. Bull. Soc. Roy. Bot. Belg. 91: 179-195.
Lazarides M. (1980) The genus Leptochloa Beauv. (Poaceae, Eragrostideae) in Australia and Papua New Guinea.Brunonia 3 (2): 247-269.
Mabberley D.J. (2008) Mabberley’s plant-book (3th ed.). Cambridge University Press, Cambridge: XVIII + 1021 p.
McNeill J. (1979) Diplachne and Leptochloa (Poaceae) in North America. Brittonia 31(3): 399-404.
Nicora E.G. (1995) Los géneros Diplachne y Leptochloa (Gramineae, Eragrosteae) de la Argentina y paíseslimitrofes. Darwiniana 33(1-4): 233-256.
Nowack R. (1994) Revision of Leptochloa Beauv. (incl. Diplachne Beauv.) (Poaceae) in Malesia. Rheedea 4(2): 79-92.
Peñaloza-Jiménez G., Peterson P.M. & Giraldo-Cañas D. (2002) Los géneros Eragrostis y Leptochloa (Poaceae: Cynodonteae) en Colombia. Hickenia 3(35): 133-141.
Peterson P.M., Romaschenko K. & Arrieta Y.H. (2015) A molecular phylogeny and classification of the Eleusininae with a new genus, Micrachne (Poaceae: Chloridoideae: Cynodonteae). Taxon 64(3): 445-467. [available online at: https://www.researchgate.net/publication/271851457_A_molecular_phylogeny_and_classification_of_the_Eleusininae_with_a_new_genus_Micrachne_%28Poaceae_Chloridoideae_Cynodonteae%29]
Peterson P.M., Romaschenko K., Snow N. & Johnson G.P. (2012) A Molecular Phylogeny and Classification of Leptochloa (Poaceae: Chloridoideae: Chlorideae) Sensu Lato and Related Genera. Annals of Botany 109(7): 1317-1330.
Snow N. (1998) Nomenclatural changes in Leptochloa P. Beau voissensulato (Poaceae, Chloridoideae). Novon 8: 77-80.
Snow N. (2003) Leptochloa. In: Barkworth M.E. & al. (eds.), Flora of North America north of Mexico, vol. 25. Oxford University Press, New York-Oxford: 51-60.
Snow N. & Peterson P.M.(2012) Nomenclatural notes on Dinebra, Diplachne, Disakisperma, and Leptochloa (Poaceae: Chloridoideae).Phytoneuron 2012-71: 1–2. [available online at: http://www.phytoneuron.net/PhytoN-Leptochloa.pdf]
Snow N., Peterson P.M. & Romaschenko K. (2013) Systematics of Disakisperma (Poaceae, Chloridoideae, Chlorideae). PhytoKeys 26: 21-70. [available online at: http://phytokeys.pensoft.net/articles.php?id=1484]
Snow N., Peterson P.M., Romaschenko K. & Simon B.K. (2018) Monograph of Diplachne (Poaceae, Chloridoideae, Cynodonteae). PhytoKeys 93: 1–102. [available online at: https://doi.org/10.3897/phytokeys.93.21079]
Snow N. & Symon B.K. (1998) Taxonomic status and Australian distribution of the weedy neotropical grass Leptochloafusca subsp. uninervia, with an updated key to Australian Leptochloa (Poaceae, Chloridoideae). Austrobaileya 5(2): 299-305.
Verloove F. & Lambinon J. (2006) The non-native vascular flora of Belgium: a new nothospecies and three new combinations. Syst. Geogr. Pl. 76: 217-220.