Rio Grande Spikerush

Description

Plants perennial, densely tufted; rhizomes mostly hidden by aerial shoots and roots, not long, 2�3 mm thick, hard, cortex persistent?, internodes very short, scales persistent, 4�7 mm, membranous, slightly fibrous. Culms terete, when dry with to 12 blunt ribs, 20�55 cm � 0.5�1.1 mm, soft to firm, internally mostly hollow with complete transverse septa 2�4 mm apart, evident only on sectioning culm. Leaves: distal leaf sheaths persistent, not splitting, proximally dark red, distally stramineous or reddish, thinly papery, apex often red to brown, obtuse to subtruncate, slightly callose, tooth present, 0.5�1(�3.7) mm. Spikelets lanceoloid, 5�13 � 2�2.5 mm, apex acute to obtuse; proximal scale amplexicaulous, entire; subproximal scale empty; floral scales appressed in fruit, 10�100, 10�12 per mm of rachilla, medium brown to stramineous, midrib regions often greenish, ovate, 1�1.5 � 1 mm, entire, apex rounded to subacute, carinate in distal part of spikelet. Flowers: perianth bristles 5�6, pale brown, stout, equaling achene; stamens 3; anthers brown, 0.4�0.9 mm; styles 3-fid or a few 2-fid in the same spikelet. Achenes falling with scales, green or medium or dark brown, obpyriform, compressed-trigonous or some biconvex in same spikelet, angles prominent, 0.6�0.8 � 0.5�0.6 mm, neck short or absent, smooth or very finely reticulate at 20�30X. Tubercles brown, depressed-pyramidal, 0.1�0.2 � 0.2�0.3 mm.