26.13   ISCHAEMUM L.
Mary E. Barkworth

Plants annual or perennial. Culms 10-350 cm, often decumbent, sometimes branched above the base. Leaves not aromatic; sheaths open; ligules membranous, glabrous or ciliate, sides often higher than the middle. Inflorescences terminal, sometimes also axillary; inflorescence units with (1)2-many rames on a common peduncle; rames secund, ascending, members of a cluster sometimes so closely appressed as to appear as one; internodes stoutly linear to clavate. Spikelets in homogamous or heterogamous sessile-pedicellate or unequally pedicellate pairs; disarticulation in the rames, below both the sessile and pedicellate spikelets. Sessile spikelets dorsally compressed; glumes subequal; lower glumes 2-keeled, keels sometimes winged; upper glumes keeled, sometimes awned; lower florets staminate; upper florets bisexual, lemmas usually bifid and awned from the sinus. Pedicels fused to the rame axes, clavate or inflated, sometimes as wide as the spikelets. Pedicellate spikelets morphologically and sexually similar to the sessile spikelets or staminate and reduced. x = 9, 10. Name from the Greek ischion, hip or hip-joint socket.

Ischaemum includes approximately 65 species, all of which are native to tropical regions of the Eastern Hemisphere. None of the species is known to be established in North America. The genus is included in this treatment because two of its species are considered serious weed threats by the U.S. Department of Agriculture.


SELECTED REFERENCESKoyama, T.1987. Grasses of Japan and Its Neighboring Regions: An Identification Manual. Kodansha, Ltd., Tokyo, Japan. 370 pp.; Reed, C.F. 1964. A flora of the chrome and manganese ore piles at Canton, in the Port of Baltimore, Maryland and at Newport News, Virginia, with descriptions of genera and species new to the flora of the eastern United States. Phytologia 10:321-405.

1
Lower glumes of the sessile spikelets not winged, rugose, with 4-5 ridges; plants annuals or short-lived perennials ..... 1. I. rugosum
Lower glumes of the sessile spikelets winged on the keels, not rugose; plants perennial ..... 2. I. indicum


1.   Ischaemum rugosum Salisb.
Ribbed Murainagrass

Plants annual, or short-lived perennials. Culms 30-130 cm, erect or geniculate at the base, simple to strongly branched below; nodes antrorsely pilose; internodes glabrous. Leaves cauline; sheaths mostly glabrous or sparsely pilose, margins ciliate distally; collars villous; ligules 1-5.5 mm; blades 8-20 cm long, 7-15 mm wide, flat, usually pilose on both surfaces, sometimes with papillose-based hairs, occasionally glabrous. Inflorescence units with 2 rames; rames 3-8 cm long, 3-4 mm wide; internodes 2.5-3.5 mm, slightly clavate distally. Sessile spikelets 3-5 mm long, 1.8-2.2 mm wide; calluses shortly pubescent; lower glumes coriaceous, yellowish, not winged, coarsely transversely rugose with 4-5 ridges on the proximal 2/3-4/5, thickly chartaceous distally and tapering to the apices; upper glumes thickly chartaceous, ciliate, awned, awns 1.5-2 cm, geniculate below the middle; anthers about 2 mm. Pedicellate spikelets varying from 0.5 mm to equaling the sessile spikelets. 2n = 18, 20, 44.

Ischaemum rugosum is native to southern Asia, and is now established in moist, tropical habitats around the world, including Mexico. It has been found in southern Texas and on chrome ore piles in Canton, Maryland, but is thought to have been eliminated from both areas. The U.S. Department of Agriculture considers it a noxious weed; plants found growing within the continental United States should be promptly reported to that agency.


2.   Ischaemum indicum (Houtt.) Merr.
Indian Murainagrass

Plants perennial, forming loose clumps. Culms 20-90 cm, decumbent, often rooting from the lower nodes; nodes antrorsely pilose; internodes glabrous. Leaves crowded towards the base; sheaths open, sparsely to densely pilose; ligules about 1 mm, membranous; blades 4-15 cm long, 3-8 mm wide, pilose on both surfaces. Inflorescence units with 2 rames; rames 3-5 cm long, 4-5 mm wide; internodes 3-4 mm long, 0.5-0.7 mm wide, slightly triquetrous. Sessile spikelets 4-5 mm long, 1.2-1.5 mm wide; calluses strigose; lower glumes coriaceous below, thickly membranous above, rough but not rugose, 5-7-veined, 2-keeled, keels narrowly winged; upper glumes 1-keeled, keels winged distally, awned, awns 1-1.5 cm; anthers 2-2.5 mm. Pedicels 2.5-3.5 mm, ciliate on the edges. Pedicellate spikelets slightly smaller than the sessile spikelets. 2n = 36.

Reed (1964) reported finding Ischaemum indicum growing on chrome ore piles in Canton, Maryland. This reported introduction has not been verified.