Sandbur

Mature Cenchrus echinatus (non-native) are easily spotted by their seed heads, loaded with spiky burs ready to attach to anything that comes their way.  For non-seeding plants, the most reliable character is the reddish color found at the basal part of the stem, and often into the upper stem and leaves, especially in older plants. Cenchrus have moderately broad, prostrate, and somewhat curled blades with a central keel. The extent of red in the plant is probably correlated with stressors such as cold temperatures or dry conditions.  The only other grass with red in the basal part of the stem is Eragrostis amabilis, from which it can generally be distinguished based on size and blade width.

The distinct keel on Cenchrus blades is a quick feature with which to distinguish it from E. variabilis. It is more obvious when seen on the bottom of the blade. Also, note the faint red edge to the blade.

The distinct keel on Cenchrus blades is a quick feature with which to distinguish it from E. variabilis. It is more obvious when seen on the bottom of the blade. Also, note the faint red edge to the blade.

This cluster of Cenchrus cotyledons largely lack red in the stem, though the right and leftmost plants show varying amounts of red.

Description: An annual grass that is erect or decumbent at the base, somewhat tufted, branched; roots fibrous; culms 25 to 90 cm tall, the lower part often prostrate, compressed, rooting at the nodes, often reddish at the nodes; leaf sheaths smooth or with few stiff hairs on the margins on the upper portion; ligule 0.5-1.7 mm long, with marginal hairs; blades smooth to hairy, 5 to 30 cm long, 0.5 to 1 cm wide, flat, lower surface smooth, upper side rough, slightly hairy at the base; inflorescence a spike, dense, cylindric, 2.5 to 10 cm long, about 1 cm in diameter; the burs five to 50 or more, not crowded, almost sessile, globular, densely arranged, 3 to 6 mm in diameter, 5 to 10 mm long; the spines or bristles 2 to 3.5 mm long, usually turning purple with age, sometimes straw-colored, the basal bristles numerous, usually turned downward, inner bristles attached below the middle of the the bur, bristles united for about one-half their length to form a deep cup, hairy, bristles irregular in size and thickness; spikelets two to four (usually three) in each bur, about 5 to 7 mm long; stamens three; grains ovoid, 1.6-3.2 mm long, 1.3 to 2.2 mm wide. The species is distinguished by the large, spiny burs, which are easily detached from the flowering spike. The burs are covered with numerous, sharp bristles, which usually turn purple with age and may be strong enough to penetrate shoe leather. There is a variety in Hawaii, variety hillebrandianus, in which the plants are softly hairy throughout rather than just at the base of the leaves (Holm et al., 1977; p. 201).