Digitaria

Digitaria Haller

Digitaria is a large genus of ca. 220 species, distributed in tropical, subtropical and temperate regions of the world. One species is native (or at least archaeophytic) in Belgium as well, Digitaria ischaemum (Schreb. ex Schweigg.) Muhlenb. (Lambinon & al. 2004).

Digitaria is a surprisingly complex genus, despite the existence of a world monograph (Henrard 1950). With the exception of the easily recognised Digitaria aequiglumis the identification of the remaining taxa in this account may turn out to be problematic in one way or another. Digitaria ischaemum and D. violascens are much more closely related than often thought (see also Veldkamp 1973, Shouliang & Phillips 2006) and most diacritic features for their distinction are variable and overlap (Verloove 2008). Likewise, Digitaria ciliaris and D. sanguinalis are often exceedingly similar and probably mere forms of one variable taxon.

Moreover, numerous infraspecific taxa have been described. Beside those treated below, Digitaria ischaemum var. mississippiensis (Gatt.) Fernald is perhaps worth mentioning (see also Zuloaga & al. 2003). It is a larger plant with 5-7 inflorescence branches, up to 15 cm long. It surely intergrades with var. ischaemum but typical plants of this variety were recently recorded on a demolition site in Leuven (08.2006).

In addition to the taxa included in this account several others may have been overlooked. In maize fields Digitaria ciliaris/D. sanguinalis-like plants with clearly dimorphic spikelets are regularly recorded: lower lemmas of the pedicellate spikelets have marginal hairs that become widely divergent at maturity, while lower lemmas of the sessile spikelets are quite glabrous. This feature was given much weight by Henrard (1950): two closely related species (Digitaria bicornis (Lam.) Roem. et Schult. and D. biformis Willd.) were accommodated by him in a separate section Biformes. These, and several other forms or races that are closely related to Digitaria ciliaris and D. sanguinalis, require further study (preferably emphasising on the molecular phylogeny of the genus). It might finally turn out that, even today, far too many species are recognised.

1 Upper lemma dark purplish at maturity. Spikelets in the middle half of the raceme ternate (in groups of 3), always less than 2,5 mm long, ovate, rounded to acute at apex. Upper glume (sub-) equal to spikelet length. Rachis always wing-margined === 2

1 Upper lemma pale at maturity. Spikelets in the middle half of the raceme binate (in groups of 2), over 2,5 mm long (if exceptionally shorter, then species perennial: D. abyssinica), lanceolate (sometimes narrowly so), acute-acuminate at apex. Upper glume (usually) less than 2/3 or (in D. aequiglumis) equal to spikelet length. Rachis wing-margined or (rarely) wingless === 3

2 Spikelets usually at least 2 mm long, rarely shorter. Spikelets usually densely hairy (at least when young) with short, curled hairs, some hairs usually with clavate apices. Inflorescence usually subdigitate with a distinct common axis, racemes usually 2-3(-4), rarely more, spreading horizontally at anthesis (at least the lowermost). Upper glume 3-5 nerved, lower lemma 5(-7) nerved, the nerves not equidistantly spaced (native) === Digitaria ischaemum

2 Spikelets usually slightly shorter than 2 mm, rarely longer. Spikelets usually less hairy (even when young) with longer, straight hairs (hairs with clavate apices absent). Inflorescence usually digitate without or with an indistinct common axis, racemes usually (2-) 3-7, long remaining erect during anthesis. Upper glume 3-nerved, lower lemma (5-) 7 nerved, the nerves closely and equidistantly spaced === D. violascens

3 Upper glume equal to the spikelet length, lower glume absent. Spikelets narrowly lanceolate, long acuminate at apex. Rachis wingless or at most 0,25 mm wide === D. aequiglumis

3 Upper glume always shorter than spikelet length, lower glume always present, sometimes vestigial. Spikelets obovoid, lanceolate, acute-acuminate at apex. Rachis often wing-margined and much wider than 0,25 mm === 4

4 Slender, rhizomatous mat-forming perennial. Spikelets 1,8-2,2 mm long, obovoid and quite glabrous. Rachis triquetrous, sometimes narrowly wing-margined. Inflorescence branches inserted along a distinct rachis, ca. 10-90 mm long === D. abyssinica

4 Annual. Spikelets always longer, acute-acuminate and usually distinctly hairy. Rachis always wing-margined. Inflorescence (sub-) digitate === 5

5 Marginal nerves of lower lemma smooth, without minute spines (or with very few spinules in the upper 1/3). Lower glume usually longer than 0,2 mm. Upper side of leaves usually glabrous or with some long scattered hairs near base === D. ciliaris

5 Marginal nerves of lower lemma with minute spinules, more or less throughout. Lower glume usually smaller than 0,2 mm. Upper side of leaves usually hairy throughout (rarely glabrous) === D. sanguinalis

Additional aliens: Digitaria acuminatissima Stapf (Afr., wool alien) and D. brownii (Roem. et Schult.) Hughes (Austr., wool alien).

 


Literature:

Gilani S.S., Khan M.A., Shinwari Z.K., Hussain F. & Yousaf Z. (2003) Taxonomic relationship of the genus Digitaria in Pakistan. Pak. J. Bot. 35(3): 261-278.

Giraldo-Cañas D. (2005) Las especies colombianas del género Digitaria (Poaceae: Panicoideae: Paniceae). Caldasia 27(1): 25-87. [available online at: http://www.revistas.unal.edu.co/index.php/cal/article/view/39314]

Henrard J.Th. (1950) Monograph of the genus Digitaria. Universitaire Pers, Leiden: XXI + 999 p.

Jansen P. (1951) Flora Neerlandica, deel 1, aflevering 2. KNBV, Amsterdam: 272 p.

Kok P.D.F., Robbertse P.J. & van Wyk A.E. (1989) Systematic study of Digitaria section Digitaria (Poaceae) in southern Africa. S. Afr. J. Bot. 55(2): 141-153.

Lambinon J., Delvosalle L., Duvigneaud J. (avec coll. Geerinck D., Lebeau J., Schumacker R. & Vannerom H. (2004) Nouvelle Flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines (Ptéridophytes et Spermatophytes). Cinquième édition. Jardin botanique national de Belgique, Meise: CXXX + 1167 p.

Ryves T.B., Clement E.J. & Foster M.C. (1996) Alien grasses of the British Isles. BSBI, London: XX + 181 p.

Sánchez-Ken J.G. (2012) A synopsis of Digitaria (Paniceae, Panicoideae, Poaceae) in Mexico, including the new species Digitaria michoacanensis. Acta Botanica Mexicana 101: 127-149. [available online at: http://actabotanicamexicana.blogspot.be/2012/10/a-synopsis-of-digitaria-paniceae.html]

Shouliang C. & Phillips S.M. (2006) Digitaria. In: Zhengyi W. & Raven, P.H. (eds.), Flora of China, vol. 22: 539-547. Science Press, Beijing & Missouri Botanical Garden Press, St. Louis. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=110153]

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]

Vega A.S., Rua G.H., Fabbri L.T. & Rúgolo de Agrasar Z.E. (2009) A Morphology-Based Cladistic Analysis of Digitaria (Poaceae, Panicoideae, Paniceae). Syst. Bot. 34(2): 312-323. [available online at: http://www.bioone.org/doi/pdf/10.1600/036364409788606325]

Vega A.S. & Rúgolo de Agrasar Z.E. (2002) Novedades taxonómicas y sinopsis del género Digitaria (Poaceae: Panicoideae: Paniceae) en Bolivia. Darwiniana 40: 171-190. [available online at: http://www.redalyc.org/articulo.oa?id=66940415]

Vega A.S. & Rugolo de Agrasar Z.E. (2005) Novedades taxonómicas y sinopsis del género Digitaria (Poaceae, Panicoideae, Paniceae) en Colombia y Venezuela. Darwiniana 43: 232-267. [available online at: http://www.scielo.org.ar/scielo.php?pid=S0011-67932005000100016&script=s...

Vega A.S. & Rúgolo de Agrasar Z.E. (2007) Novedades taxonómicas y sinopsis del género Digitaria (Poaceae: Panicoideae: Paniceae) en América Central. Darwiniana 45: 92-119. [available online at: http://core.kmi.open.ac.uk/display/5393095] 

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. [available online at: http://www.ville-ge.ch/cjb/publications/cando632/C632_227-233.pdf]

Webster R.D. (1984) A revision of the genus Digitaria Haller (Paniceae: Poaceae) in Australia. Brunonia 6: 131-216.

Webster R.D. (1987) Taxonomy of Digitaria section Digitaria in North America (Poaceae: Paniceae). Sida 12(1): 209-222.

Webster R.D. & Shaw R.B. (1982) Relationship between Digitaria milanjana (Poaceae: Paniceae) and the annual species of Digitaria section Digitaria in North America. Sida 9: 333-343.

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.

Zuloaga F.O., Morrone O., Davidse G., Filgueiras T.S., Peterson P.M., Soreng R.J. & Judziewicz E. (2003) Catalogue of New World Grasses (Poaceae): III. Subfamilies Panicoideae, Aristidoideae, Arundinoideae, and Danthonioideae. Contr. U.S. Nat. Herb. 46: 1-662.

Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith