| Ischaemum rugosum | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Monocots |
| Clade: | Commelinids |
| Order: | Poales |
| Family: | Poaceae |
| Subfamily: | Panicoideae |
| Genus: | Ischaemum |
| Species: | I. rugosum |
| Binomial name | |
| Ischaemum rugosum | |
Ischaemum rugosum, also known assaramollagrass, is aflowering plant belonging to the grassfamilyPoaceae in the genusIschaemum, and is native totropical andtemperate regions ofAsia, growing inmarshes and other wet habitats.[1] It is a vigorousannual, and is aninvasive species inSouth America andMadagascar.[2] It reaches heights of up to 1 m and is primarily recognized by the ridged surface of itssessile spikelet’s lowerglume.[3] Despite its historic importance asfodder in Asia, the grass has become a major weed in mid-latituderice paddies throughout Asia and South America.[4]
Ischaemum rugosum is a resilient annual that inhabits marshes and other wet habitats, growing in loose clumps to heights of 10–100 cm.[3][5] The species is primarily recognized by the wrinkled texture of the sessile spikelet’s lower glume, with 4–7 distinct horizontal ribs.[3] The plant produces brown,ovoidgrains 2 mm long.[6]
The culms are wrapped by a papery, loose leaf sheath up to 16 cm long, with bulbous-based hairs at the node base and sheath margin.[3][6] Sheaths are topped with a membranous ligule 6 mm deep.[3] The linear leaf blades are 5–30 cm long and 3–15 mm wide, gradually tapering down at the base and sometimes resembling a petiole.[3][5] Blades have a margin of stiff minute hairs, and may either be smooth or covered with thin hairs on the leaf surface.[3]
Theinflorescence may be terminal or axillary, and is composed of tworacemes, tightly back to back, and typically 3–12 cm long.[3][5]Spikelets on each raceme are in pairs; one spikelet isfertile and sessile, and the other issterile andpedicelled.[5][6]
Sessile spikelets are 4–6 mm long and contain two florets, one sterile and one fertile; the pair lack arachilla extension between them.[5] The awn of the upper lemma reaches up to 2 cm.[3] Glumes are unalike; the lower glume is ovate with a ridged, convex surface, and the upper is thinner and boat-shaped.[3][5]
The pedicelled spikelets may be highly reduced or well-developed, and are at least as long as the sessile spikelets, or shorter (2–6 mm long).[3][5] The pedicel is typically 1 mm long and stout, and spikelet’slemmas are usually empty andawnless.[5][6] The glumes are papery, and ovate to pointed with a blunt apex.[5][6]
The genus Ischaemum L. takes its name from theLatinischaemon (Greekischo “to restrain” andhaima “blood”), as recorded byPliny the Elder to describe an herb used to stop bleeding.[1] As circumscribed byLinnaeus, thegenus contained some species whose seeds had been known to havestyptic properties, and so the name was inherited.[1] The specific epithetrugosum authored bySalisbury is derived from the Latinrugosus “wrinkled”, and refers to the wrinkled lower glumes on the sessile spikelets.[6]
The species grows in water, wet grasslands, moist river banks, and drainage ditches, and is important to grazing animals in the regions to which it is native.[1] Its vigorous nature gives it a high invasive potential, and it is a well-known agricultural weed throughout the moist tropics.[1] Within the optimum temperature range of germination from 20–30 °C, a 2015 study observed a 97.5% germination rate in lab conditions, which attests to its competitiveness as an invasive species.[4] However, germination is restricted to sufficiently moist soil, and completely inhibited in darkness, which may inform future directions in weed management.[4]
Ischaemum rugosum occupies a wide native distribution in tropical and temperate regions of Asia, Africa, and Oceania.[1][2] However, it has extended its range as an invasive species within the mid-latitudes of Latin America.[2]
Taxonomists recognize five sections within the genusIschaemum, placingIschaemum rugosum within the section Aristata (recognized by arugose lower glume and awnless upper glume on the sessile spikelet).[7] The species was first described formally by the British botanistRichard Anthony Salisbury in 1791, in his publicationIcones Stirpium Rariorum Descriptionibus Illustratae.[8] Symptomatic of its extensive distribution, the species has accumulated 20synonyms across 7 genera; however, as presently recognized, the species adopts Salisbury’s original classification.[2] Since the species inhabits such a wide native range from tropical Africa to southern Asia, it goes by a myriad of regional names as well (e.g.fovo in Sierra Leone,amarkarh in parts of India,môm u in Vietnam, andka-gyi-the-myet in Myanmar).[1]
Ischaemum rugosum belongs toPoaceae (Graminae), an economically important group and the fifth largestAngiosperm family (with 11,506 species).[9][10] The genusIschaemum has undergone several iterations of supergeneric classification within thetribe Andropogoneae, in the subfamily Panicoideae; these disagreements owe largely to the high degree of variation over a morphological continuum in Andropogoneae, which has made it a challenge to circumscribemonophyletic subdivisions.[11] Earlymolecular phylogenetic revisions of the Andropogoneae suggested its majorlineages arose from a rapidevolutionary radiation, in which such case the circumscription of well-supported subtribes would be difficult, if not arbitrary.[12] However, the most recent synthesis ofmorphological and molecular data presents a phylogenetic classification that recognizes the genusIschaemum within subfamily Panicoideae, supertribe Andropogonodae,tribe Andropogoneae, subtribe Ischaeminae.[10] Several previously recognizedvarieties have been reduced tosynonymy.[2]
Besides the grain occasionally being used as food, the species has historically been economically important as forage for horses and cattle, and harvested as hay.[1] However, its greatest economic impact has been as a noxious weed in vegetable and rice fields in countries includingIndia,Thailand,Ghana,Brazil,Venezuela, andMalaysia.[1][4] A study in India reported that an outbreak ofIschaemum rugosum can reduce a rice paddy yield by up to 69.4%.[13] One challenge is that the young shoots of the plant resemble the rice growing in the fields.[1] But a greater concern is that over the past several decades, it has evolved resistance to several commonly used herbicides.[14] Presently, the most effective weed management strategies recognized are cultural methods, such as mulching with rice residue and shallow tillage.[4]