Syntherisma sericea Honda
Annual; culms 20-100 cm high, decumbent at the base and geniculately ascending. Leaf-blades broadly linear, 3-25 cm long, 3-10 mm wide. Inflorescence digitate or subdigitate (axis up to 5 cm long in robust specimens), composed of 2-12 racemes; racemes stiff, 6-22 cm long, sometimes adorned with sparse long white hairs, the spikelets binate and overlapping by about two-thirds their length on a winged rhachis with triquetrous midrib; pedicels triquetrous, scabrid, obtuse or slightly expanded at the tip. Spikelets narrowly elliptic, (2-)2.5-3.3 (-3.7) mm long, sharply acute; lower glume distinct, 0.2-0.4 mm long and triangular; upper glume at least half as long as the spikelet, typically two-thirds to three-quarters as long, 3-nerved; lower lemma as long as the spikelet, 7-nerved, the nerves smooth and evenly spaced or with a wide interspace flanking the midrib (sometimes those of the subsessile spikelet even and of the pedicelled spikelet spaced), appressed puberulous, silky pubescent or rarely shortly villous, often encompassed by a ciliate frill, occasionally glabrous, one or both spikelets often beset with stiff glassy bristles; fruit ellipsoid, grey to light brown.
Fl. & Fr. Per.: July-October.
Type: China, Wennerberg (LD).
Distribution: Pakistan (Sind, Punjab, N.W.F.P. & Kashmir); common throughout much of the tropics.
Paspalum sanguinale (Linn.) Lam. var. rottleri Hook.f. is typified by two sheets, Wight 3032 and Wight 3033, both at Kew. Of these, the former is Digitaria ciliaris and the latter Digitaria bicornis (Lam.) Loud. In the protologue to the variety, Hooker described the wings of the rhachis as being “two or three times broader than the midrib.” Since this character does not agree with Digitaria bicornis (including Wight 3033), the specimen Wight 3032 is selected as the lectotype of var. rottleri. This is included in the synomymy of Digitaria ciliaris because the spikelets are narrow and apparently lack the spiny protuberences on the nerves of the lemma.
Digitaria ciliaris is a polymorphic species showing at least four parallel series based on quite independent sources of variation. The rhachis may have long white hairs (rhachiseta) or not; in terms of indumentum the spikelets of a pair may be the same or different (biformis); the spikelets (independently in each pair) may be glabrous (nubica), long or short hairy (ciliaris, desvauxii) or conspicuously fringed (criniformis, fimbriata); one or both spikelets may be beset with stiff glassy bristles (chrysoblephara, willdenowii). None of these variants shows any indication of geographical segration, and since there are at least these four independent sources of variation the number of potential varieties is enormous, but none would be of any taxonomic significance. The sporadic occurence of the siliceous spines characteristic of Digitaria sanguinalis in spikelets otherwise typical of Digitaria ciliaris suggests that there may be some gene-flow between these two species in Pakistan.
Digitaria bicornis (Lam.) Loud. is often included in subsp. chrysoblephara (or vice versa, see Veldkamp 1973) by virtue of its possession of glassy bristles, but like Digitaria ciliaris it too shows several types of indumentum and quite frequently is perfectly glabrous (even to the exclusion of the glassy bristles). It is in fact a distinct species differing in a number of important characters. There are normally only 2, sometimes 3 racemes each with a slightly swollen base. The midrib is thick and the wings are usually extremely narrow. The pedicels are stout and straight and this, combined with the thick midrib, gives the spikelets the appearance of being sunk in the rhachis. The lower lemma is horny with much thickened, contiguous or closely spaced nerves. The first pair of interspaces, and the second where present, are reduced to deep V-shaped grooves. The lemma characters are best seen in the subsessile spikelets towards the base of the raceme. True Digitaria bicornis does not occur in Pakistan, being confined to the warmer parts of southern India, Sri Lanka and Burma.
Digitaria ciliaris is a widespread tropical weed.