Beach Wiregrass

Dactyloctenium was first found on Kure in 2008. It is a high priority for eradication but unfortunately has spread to several widespread sites on the island. It is most readily identified by its wavy leaf margin, which can be seen in the photo below.

Dactyloctenium cotyledons are difficult to observe. Early leaves often wither and die (below left), leaving a sheath from which later blades grow. In some conditions, the cotyledon will persist, though, and one can be seen in the photo below right, the blade pointing upward to the left. The cotyledons, like in most grasses, are relatively long and narrow, with little taper until very near the end.

At very small sizes Dactyloctenium true leaves are very similar to Setaria, with wide tapered blades of roughly the same size. In the photos below Dactyloctenium is on the left, Setaria on the right. 

Though difficult to discern without magnification, beach wiregrass can be distinguished from Setaria, and from other broad-bladed non-native grasses, based on the presence of fine teeth on the blade margin.  In botanical terms, the blades are described as ‘papillose-hispid, especially along margins’, where hispid refers to the rough texture caused by the presence of stiff hairs, bristles, or minute teeth.

At later stages Dactyloctenium tends to be very crowded, producing many densely crowded broad blades, and many tightly clustered additional stems. By this stage, the wavy leaf margins are also generally easy to see. 

In large plants, Dactyloctenium is still probably most similar to Setaria, with broad blades, and stems growing radially out from a central point. In general, Dactyloctenium is darker green, and as the stems become long they develop joints, or nodes, one of which is visible in the photo below left, in the stem pointing upward and to the right. Dactyloctenium will re-root at these nodes, which leads to the mat-forming characteristic of this grass.

Beach wiregrass seed heads are somewhat similar to Eleusine but with more numerous, short spikes (3-9) and larger seeds. 

Description: Slender to moderately robust, spreading annuals; culms 70-100 cm tall, usually geniculately ascending and rooting at lower nodes, usually stoloniferous and mat-forming. Sheaths 2.5-4 cm long, compressed, glabrous or with a few bulbous-based hairs on the keel; ligule a narrow fimbriate membrane; blades flat, 3-25 cm long, 2.5-7.5 (-12) mm wide, papillose-hispid, especially along margins. Inflorescences composed of (1-) 3-9 linear to narrowly oblong spikes 1.2-6.5 cm long, ascending to radiating horizontally from top of culm; spikelets 3-4-flowered, broadly ovate, 3.5-4.5 mm long; glumes subequal, 1.5-2.2 mm long, first glume lanceolate in profile, keel thick, scabrid, second glume elliptic to narrowly

obovate in profile, keel smooth, prolonged into a stout, divergent, scabrid awn 0.5-2 times as long as the glume; lemmas narrowly ovate to ovate in profile, 2.6-4 mm long, keel gibbous, concave and scabrid above the middle and usually prolonged into a stout cusp or mucro up to 1 mm long; palea keels more or Dactyloctenium aegyptium (PIER species info) 1 of 21 8/1/11 1:35 PM less winged. Caryopsis broadly obovate to triangular, ca. 1 mm long, transversely rugose (Wagner et al., 1999; pp. 1521-1522).