4. Digitaria violascens Link (syn.: D. chinensis (Nees) A. Camus) (trop.) – An exceptional and ephemeral grain alien, recorded once in 1994 in the port of Antwerpen (but possibly overlooked; see below). Also grown from soybean waste in 1998.
Digitaria violascens is very reminiscent of native D. ischaemum but usually has smaller, less hairy spikelets. Both are usually distinguished without difficulty in most floras on hair characters only (and have even been accommodated in different sections on this feature only by Henrard 1950). However, in practice distinction is not always clear-cut without strong magnification. As a matter of fact all characters usually provided for their distinction are variable and overlap. Digitaria ischaemum is fairly constant in spikelet length (2-2,5 mm on average) but, as correctly pointed out by Veldkamp (1973), D. violascens has in fact two more or less distinct forms: a small-spikeleted form with spikelets (1,2-) 1,3-1,6 mm long and a larger-spikeleted form (including the type!) with spikelets (1,6-) 1,7-2 (-2,5) mm long. The latter form thus can have larger spikelets than small-spikeleted forms of Digitaria ischaemum. They are possibly better treated as mere variants of one variable species. Radford (1964) provided a combination at varietal rank (as Digitaria ischaemum var. violascens (Link) Radford).
Digitaria violascens is a widely naturalised but long overlooked xenophyte in parts of southern Europe (Verloove 2008, Verloove 2010).
Spikelet indumentum of Digitaria ischaemum (SEM)
Spikelet indumentum of Digitaria violascens (SEM)
Henrard J.Th. (1950) Monograph of the genus Digitaria. Universitaire Pers, Leiden: XXI + 999 p.
Radford J. (1964) Digitaria ischaemum var. violascens. In: Ahles H.E. (ed.), New combinations for some vascular plants of southeastern United States. J. Elisha Michell Sci. Soc. 80: 172-173.
Veldkamp J.F. (1973) A revision of Digitaria in Malesia. Blumea 21: 1-80.
Verloove F. (2008) Studies within the genus Digitaria Haller (Poaceae: Panicoideae) in southwestern Europe. Candollea 63(2): 227-233.
Verloove F. (2010) Invaders in disguise. Conservation risks derived from misidentification of invasive plants. Management of Biological Invasions 1: 1-5.
Verloove F. & Vandenberghe C. (1996) Nieuwe en interessante voederadventieven voor de Belgische flora, hoofdzakelijk in 1995. Dumortiera 66: 11-32.