2. Digitaria ciliaris (Retz.) Koeler (syn.: D. adscendens (Kunth) Henrard, D. marginata Link) (trop.) – A regular but poorly known alien, known at least since 1828. Seen most years now, these days usually as a grain alien. Probably often overlooked as and confused with Digitaria sanguinalis. Hence, the actual degree of naturalisation of Digitaria ciliaris remains uncertain. A recent and local naturalisation, in maize fields or even in urban areas (see Clement 2000), is not unlikely.
Digitaria ciliaris appears to be the (sub-) tropical counterpart of the more temperate D. sanguinalis. Typical plants of both are easily distinguished (see key) but more or less intermediate forms regularly occur and the specific boundaries, if any, remain unclear. According to Henrard (1950) the marginal nerves of the lower lemma are perfectly smooth whereas some modern floras (see for instance Wipff 2003) admit that the lower lemmas are “usually smooth, occasionally the lateral veins scabridulous on the distal 1/3 margins (…)”. Indeed, even in “typical” specimens of Digitaria ciliaris one will usually find at least some prickles on at least some marginal nerves. As such, it is unclear where Digitaria sanguinalis begins and D. ciliaris ends!
In Belgium two more or less distinct subspecies occur (see key below), subspecies ciliaris being the more regular one. Subspecies nubica (Stapf) S.T. Blake – confined to the (sub-) tropics in Africa – was recently recorded as a grain alien in Izegem (1998), Roeselare (2003) and Gent (2007). Since 2008 it has been recorded in some maize fields in Flanders as well (Knesselare, Lovendegem,…), possibly from discarded birdseed waste. At least in Knesselare it seems well established (comm. I. Hoste). Its presence in commercial birdseed mixtures (incl. pheasant feed) was also confirmed in Oosterzele in 2009 (sown on arable land by game keepers). The separation of subsp. nubica is remarkably straightforward in Belgium: plants are always very robust, erect, with perfectly smooth lower lemmas and rather gibbous upper lemmas. It is, in fact, much more distinct from subsp. ciliaris, than the latter is from Digitaria sanguinalis. Therefore, it is surprising that subsp. nubica is simply included in Digitaria ciliaris by most modern taxonomists, even in its presumed area of origin (Phillips 1995). Both subspecies are distinguished in the following couplet:
- Upper glume more than ½ spikelet length. Plant often decumbent, rooting at the nodes === subsp. ciliaris
- Upper glume less than ½ spikelet length. Plant usually more robust, erect === subsp. nubica
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Selected literature:
Clement E.J. (2000) Digitaria ciliaris established in Gosport (S. Hants, V.C. 1). BSBI News 83: 37-39.
Ebinger J.E. (1962) Validity of the grass species Digitaria adscendens. Brittonia 14 : 248-253.
Henrard J.Th. (1950) Monograph of the genus Digitaria. Universitaire Pers, Leiden: XXI + 999 p.
Phillips S.M. (1995) Poaceae. In: Hedberg I. & Edwards S. (eds.), Flora of Ethiopia and Eritrea. Vol. 7. The National Herbarium, Addis Ababa University, Addis Ababa (Ethiopia) and Department of Systematic Botany, Uppsala University, Uppsala (Sweden): 420 p.
Vázquez Pardo F.M., Márquez García F. & Blanco Salas J. (2014) Anotaciones corológicas a la flora en Extremadura 084.- Digitaria ciliaris (Retz.) Koeler. Folia Botanica Extremadurensis 8: 86-91. [available online at: http://jolube.files.wordpress.com/2010/01/folia_botanica_extremadurensis_8_2014.pdf]
Verloove F. & Vandenberghe C. (1996) Nieuwe en interessante voederadventieven voor de Belgische flora, hoofdzakelijk in 1995. Dumortiera 66: 11-32.
Verloove F. & Vandenberghe C. (1999) Nieuwe en interessante voederadventieven voor de Belgische flora, hoofdzakelijk in 1998. Dumortiera 74: 23-32.
Webster R.D. & Hatch S.L. (1981) Taxonomic relationships of Texas specimens of Digitaria ciliaris and Digitaria bicornis (Poaceae). Sida 9: 34-42.
Wilhalm T. (2009) Digitaria ciliaris in Europe. Willdenowia 39: 247-259.
Wipff J.K. (2003) Digitaria. In: Barkworth M.E. & al. (eds.), Flora of North America north of Mexico, vol. 25. Oxford University Press, New York-Oxford: 358-383.