Cenchrus spinifex
Cenchrus tribuloides
coastal sandbur, common sandbur
dune sandbur, sanddune sandbur
30-100 cm, geniculate.
10-70 cm, decumbent, branching and rooting at the lower nodes.
compressed, glabrous or sparsely pilose;
ligules 0.5-1.4 mm;
blades 3-28 cm long, (1)3-7.2 mm wide, glabrous or sparsely long-pilose adaxially.
compressed, glabrous or pubescent;
ligules 1-2.1 mm;
blades 2-14 cm long, 3-14.2 mm wide.
3-5(8.5) cm;
fascicles 5.5-10.2 mm long, 2.5-5 mm wide, imbricate, ovoid to globose, glabrous or sparesely to moderately pubescent;
outer bristles, when present, mostly flattened;
inner bristles 8-40 (rarely more), 2-5.8 mm long, 1-2 mm wide, fused at least 1/2 their length, forming a distinct cupule, the distal portions usually diverging from the cupule at multiple, irregular intervals, sometimes diverging at more or less the same level, ciliate at the base, pubescent, stramineous to mauve or purple, flattened.
2-8.2 cm;
fascicles 9-16 mm long, 4-8 mm wide, imbricate, ovoid, densely pubescent;
bristles 15-43;
outer bristles usually present, flattened or terete;
inner bristles 4-8 mm long, 1.2-3 mm wide, fused for at least 1/2 their length, forming a distinct cupule, the distal portions diverging at irregular intervals from the cupule, stramineous or purple.
2-4 per fascicle, 3.5-5.9 mm, glabrous.
1(2) per fascicle, 6-8.8 mm.
about 2.5 mm long, 1-2 mm wide, ovoid.
2.6-4 mm long, 2.2-3.1 mm wide, ovoid-elliptic.
glumes 1-3.3 mm;
upper glumes (2.8)3.5-5 mm, 5-7-veined;
lower florets sometimes staminate;
lower lemmas 3-5(5.9) mm, 5-7-veined;
lower paleas sometimes reduced or absent;
anthers 1.3-1.6 mm;
upper lemmas 3.5-5(5.8) mm;
anthers 0.5-1.2 mm.
glumes 1-4 mm;
upper glumes 4.9-6.8 mm, 3-7-veined;
lower lemmas 5.5-7.5 mm, 3-7-veined, enclosing the palea;
upper lemmas 6-8.7 mm;
anthers 0.8-2.8 mm.
= 34 (32).
= 34.
Cenchrus spinifex
Cenchrus tribuloides
Cenchrus spinifex is common in sandy woods, fields, and waste places throughout the southern United States and southwards into South America. It may be more widespread than shown in the northern portion of the contiguous United States because it has often been confused with C. tribuloides. Cenchrus spinifex differs from C. tribuloides in its glabrous or less densely pubescent fascicles, narrower inner bristles, and larger number of bristles. It has also been confused with C. longispinus but differs in having shorter spikelets, fewer bristles overall, wider inner bristles, and outer bristles that are usually flattened rather than usually terete.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Cenchrus tribuloides grows in moist, sandy dunes and is restricted to the eastern United States. It differs from C. spinifex in its larger spikelets and smaller number of spikelets per fascicle, and from C. longispinus in its densely pubescent fascicles, fewer bristles, and wider inner bristles.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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