Paspalidium geminatum
(Egyptian paspalidium)

Identity

Preferred Scientific Name

• Paspalidium geminatum (Forsskål) Stapf

Preferred Common Name

• Egyptian paspalidium

Other Scientific Names

• Echinochloa geminata (Forsskål) Roberty
• Panicum brizoides Lamarck
• Panicum fluitans Retzius
• Panicum geminatum Forssk.
• Panicum paludivagum Hitchc. & Chase, Contrib.
• Panicum paspalodes Persoon
• Paspalidium geminatum subsp. paludivagum (Hitchc. & Chase) Catasús
• Paspalidium geminatum var. paludivagum (Hitchc. & Chase) Gould,
• Paspalidium paludivagum Parodi
• Setaria geminata (Forsskål) Veldkamp.
• Setaria geminata var. paludivaga (Hitchc. & Chase) R. D. Webster

International Common Names

• English: watercrown grass

Local Common Names

• Mali: baugassongau; marbéré
• Nigeria: angarago; geron tsíntsííyáá; hákóórín karee; mákòòrín karee; tùmbín kúúsúù
• USA: alligator grass; Egyptian panic grass; water paspalidium
• USA/Florida: Kissimmeegrass

Summary of Invasiveness

P. geminatum is a globally-distributed grass that is an important component of marshes and emergent grasslands in tropical, dry, and warm temperate climates defined by well-marked dry and rainy seasons. P. geminatum contributes to unique and diverse wetland communities. It can become locally abundant under extended warm season flooding, but is not considered introduced, invasive, or problematic in these natural environments. P. geminatum has become problematic in arid climates where urbanization, irrigation and drainage projects have caused massive alterations in soil and hydrologic regime. It can spread through irrigation canals, open waste ditches and polluted riparian systems, compromising water flow and flood control.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Monocotyledonae
•                     Order: Cyperales
•                         Family: Poaceae
•                             Genus: Paspalidium
•                                 Species: Paspalidium geminatum

Notes on Taxonomy and Nomenclature

Paspalidiumgeminatum was discovered in 1761 by Pehr Forsskål during the first year of a Royal Danish natural history expedition to Egypt and Yemen. The collection was made near the town of Rashid, also called Rosetta, in the Nile Delta region of northern Africa. The holotype remains at the Natural History Museum of Denmark, Copenhagen (view specimen at: http://plants.jstor.org/specimen/c10002722).

Years later Forsskål’s vouchers were reassembled and published by Niebuhr who, assuming editorship only, placed Forsskål as author of the work (Forsskål, 1775; Friis, 1983). Forsskål’s name, Panicumgeminatum, was retained for the holotype.

The current, globally accepted name is Paspalidiumgeminatum (Forssk.) Stapf, first published in volumes nine of ten of the multi-authored Flora of Tropical Africa (Prain, 1920), produced between 1868-1937. The authority Otto Staph, a specialist in the Poaceae of the Old World Tropics (Anonymous, 1933), distinguished the new genus Paspalidium from Panicum.

Subsequent changes in the use of genera stem from disagreement among grass specialists on the separation of Paspalidium from Setaria, as characterized by inflorescence structure, including the presence of a point extending beyond the terminal spikelet, spikelets and bristles (Webster 1987, 1993; Hitchcock and Chase, 1910). Veldcamp (1994) concluded as well that, based on natural gradations in key character traits, Paspalidium cannot be distinct from Setaria, thus explaining his 1994 application of the name Setaria geminata (as used by PROTA4U; PROTA, 2014). Such nomenclatural changes, however, have little bearing on field or in-hand identification of the species and its distinction from closely related taxa, which are typically accomplished under the genus Paspalidium.

Infra-specific entities have been presented, primarily from western hemisphere material (see Identity section table), yet the general consensus remains to treat all as conspecific with the species Paspalidium geminatum (Forsskål) Stapf (see Similarity to other Species to distinguish taxonomically related species).

The internationally preferred common name, Egyptian paspalidium, originates from the locality of the type specimen. Some of the locally used common names include the West African hákóórín kàréé, which translates as ‘dog’s tooth’ (Burkill, 1985), well suited to the enamel-like fruits of ripe spikelets. Another name from the same region is tùmbín kúúsúù, which equates to ‘mouse’s stomach’, though the meaning may be lost in translation (Burkill, 1985). In central Florida fishermen and biologists use the name Kissimmeegrass for offshore stands in large lakes of the Kissimmee River basin.

Description

Description taken from GrassBase (Clayton et al., 2006) with minor modifications from Godfrey and Wooten (1979) and from material reviewed by the author:

A wholly glabrous, perennial grass spreading from culms bending and rooting at lower nodes. Culms compressed above, becoming hollow and inflated, ascending and emergent to 100cm, green sheaths tight, becoming dry and ragged, blades flat to folded and tapering to the tip, inflorescence elongated, flattened, and unbranched, sparingly composed of short, upright to appressed racemes (10-18) on which the ovate spikelets are alternately arranged.

Rhizomes: creeping or floating, spongy to a degree, sometimes in floating mats.

Culms: decumbent, spreading and rooting at the lower nodes; stems slender or to 1 cm across basally, compressed, ascending and emergent from 10 to 100 cm or even higher, hollow and inflated below.

Leaf sheaths: tightly wrapped, later becoming swollen and ragged; often longer than the internodes, glabrous.

Ligule: a ring of hairs up to 1 mm long.

Leaf blades: up to 45 cm long and 17 mm wide, long-tapering, linear, flat to convolute, the long tapering tips involute; mostly glabrous (or with minute hairs at base of upper surface); margins scabrous. Basal leaves do not differ from stem leaves.

Inflorescence:  
Principle axis 5–30 cm long; flattened, unbranched. Rachis narrowly winged; with sharp-edged midrib; angular; 0.5–1 mm wide; terminating in a barren, inconspicuous extension; bearing alternately, relatively short-ascending or appressed-ascending, spikelike fertile branches (racemes).
Racemes flattened; unilateral; 0.5–4 cm long carrying spikelets, alternate in two rows on one side of the 3-angled rachis, the apex shortly pointed and free beyond the seating of the uppermost spikelet (not bristle-like).

Fertile spikelets: sessile or pedicelled; 1–2 in the cluster, pedicels oblong, 0.5–0.75 mm with tiny spines. Spikelets comprising 1 basal sterile florets; 1 fertile florets; without rachilla extension. Spikelets ovate to oblong-elliptic; dorsally compressed; 1.6–3.3 mm long (and longer); falling entire.

Glumes: glumes dissimilar; shorter than spikelet; thinner than fertile lemma. Lower glume short, as broad as they are long or broader than long, somewhat orbicular, apex truncate; 0.5 – 1mm long; 0.2–0.4 length of spikelet; membranous; pallid; without keels; 0–5 -veined. Upper glume elliptic; 0.6–0.8 length of spikelet; membranous; without keels; 5 -veined. Upper glume lateral veins transversely connected at apex. Upper glume apex obtuse, or acute.

Florets: basal sterile florets male; with palea. Lemma of lower sterile floret similar to upper glume; elliptic; 1 length of spikelet; membranous; 5-veined; obtuse, or acute. Fertile lemma elliptic; 1.2–2.4 mm long; indurate; dark brown; shiny; without keel; 5-veined. Lemma surface granulose; unwrinkled, or rugulose. Lemma margins involute. Lemma apex obtuse, or acute. Palea reflexed at apex; indurate.

Distribution

Africa: north, Macaronesia, west tropical, west-central tropical, northeast tropical, east tropical, southern tropical, south, middle Atlantic ocean, and western Indian ocean. Asia-temperate: western Asia and Arabia. Asia-tropical: India, Indo-China, and Malesia. North America: central USA, south-central USA, southeast USA, and Mexico. South America: Mesoamericana, Caribbean, northern South America, western South America, Brazil, and southern South America (Clayton et. al., 2006).

To the extent of the literature and specimen voucher data reviewed herein, P. geminatum can be determined with certainty as having been introduced to the island of St. Helena, in the mid-Atlantic Ocean, and to a single location in Missouri, USA. Although generalized sources suggest the species as potentially introduced to Madagascar and nearby islands, as well as Namibia and South Africa, supportive data was not located in this review. Further study of monographs and specimens could clarify the status of origin in these regions.

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Risk of Introduction

P. geminatum is more likely to become a problematic plant due to changing conditions in places where it is already present, rather than through its introduction into a novel region. Substrate and hydrologic disturbance, caused by urbanization, irrigation and drainage projects, appear to select for P. geminatum over the previously existing taxa. This selection is probably due to the proficiency of P. geminatum to root and colonize from stem cuttings, whereas associated taxa are more dependent on dormant seed, either on the soil surface or in the seed bank, for regeneration (Peart, 1984). In such disrupted environments of arid climates, where P. geminatum does particularly well by reproducing clonally, the prerequisites for germination and establishment of wetland seeds can be hard to meet (Baskin and Baskin, 1998) and re-vegetation of other species presumably rare.

P. geminatum is adept at colonizing compacted and denuded soils from stem pieces and in fact has been exploited for this purpose (Pouder et al., 2006).

Habitat

Across its broad pantropical zone, P. geminatum contributes to many types of floristically diverse habitats within wetland and lacustrine systems (see Environmental Services). This is due in part to its highly plastic response to changes in both environmental factors and climatic season. It is locally common in seasonally inundated grasslands, wet sand banks, marshes, shorelines and in water up to 2 m deep. P. geminatum functions as a primary coloniser of newly flooded lake beds, forming broad, emergent zones that quickly act as wave buffers and allow other species to establish, for example in Tanzania (Welsh and Denny, 1978) and Florida (Pouder et al., 2006).

During the summer it can dominate the emergent zone, later sharing dominance with other graminoids, and in the winter it provides a filtered backdrop through which smaller broad-leafed species can exploit (Billore and Vyas, 1981). It is well recognized for its role in building luxuriant floating mats with larger broad-leafed species along lake margins (Misra, 1976). In shallow lakes of Eastern Africa, as in Florida, P. geminatum forms unique offshore, open stands in water up to 1.8 m deep (Lock, 1973; Welsh and Denny, 1978; Jacono pers. obs.). Following long dry periods, however, its habitat can soon alter to broad wet prairies (Gopal, 1994).

P. geminatum is tolerant to exposure off windy shorelines. Offshore stands have remained rooted even after hurricane upheaval of most other species (Welch, 2009).

P. geminatum is adept at colonizing compacted and denuded soils from stem pieces and in fact has been exploited for this purpose (Pouder et al., 2006).

Particularly in arid climates or in warm temperate regions with dry periods (especially during winter), P. geminatum has been considered an ‘invasive’ or ‘ruderal weed’, even within its native range (Holzener, 1978). Such is the case in arid regions where urbanization, irrigation and drainage projects have caused massive alterations in not only substrates and their chemical constituents, but in the entire hydrologic system, such as in Egypt (Shaltout et al., 1995), Pakistan (Muhammad et al., 2008) and Mexico (Gomez Mendez, 2000). In the lower Nile Delta, traditional marshes have been lost to moist flats for raising crops, isolated wetlands and soil salinization (Lind and Morrison, 1974).

While in itself P. geminatum does not appear to need conservation measures, the expansive wetland landscapes it helps define are increasingly threatened by water consumption and land use practices, engineered disturbance to hydrologic systems, contamination, and even mining activities. Indeed, many wetlands of which P. geminatum is integral have been designated conservation ranking, including addition to the Ramsar List of Wetlands of International importance, such as swamps in Togo (De Foucuault et al., 1999), Lake George, Uganda (Lock, 1973), Lake Chilwa, Malawi (Howard-Williams 1977), Upper Ganges marshes (Misra, 1976); Keoladeo Ghana National Park, India (Gopal 1994) and the Everglades, USA (Noe et al., 2002).

Habitat List

Biology and Ecology

Genetics

Chromosome number 2n = 18 (Missouri Botanical Garden, 2014).

Reproductive Biology

This perennial grass has C4 photosynthesis. It produces seed throughout the year but it is better known for its clonal tendencies, especially at disturbed sites. Plants readily root and shoot from fragments of buried stems (Pouder et al., 2006).

Associated Species

Natural Areas

India: In seasonal wetlands, following extended dry periods, P. geminatum is primarily associated with other graminoids: Paspalum scrobiculatum, Echinochloa colonum, Eleocharis plantaginea, Cyperus articularis, and Ceratophyllum muricatum (Gopal, 1994). During the wet season it co-dominates with the annual sedge Cyperus iria. In the winter it grows with more delicate emergents such as Bacopa monnieri and Dopatrium junceum (Billore and Vyas, 1981).

Uganda: P. geminatum is found along the sandy, exposed shorelines of Lake George with Panicum repens and Cynodon dactylon (Lock, 1973).

Lake Victoria, Eastern Africa: Common on the water’s edge with the emergent grasses and sedges Cyperuspapyrus, Eleocharis acutangula, Scirpus inclinatus and Vossia cuspidata (Lind and Morrison, 1974).

Shark River Slough, Everglades National Park, Florida, USA: Grows in oligotrophic, long hydroperiod marshes (i.e. marshes with a long period of inundation) with Utricularia purpurea, Eleocharis cellulosa, Panium hemitomon, Sagittaria lancifolia, Pontederia cordata, Nymphoides aquatica, Nymphaea odorata and Eleocharis elongata (Noe et al., 2002).

Dammed Reservoirs

Tanzania: Dominates large sections of the lake vegetation (with Cyperusalopecuroides and Typhadomingensis) at Nyumba Ya Mungu Reservoir (Welsh and Denny, 1978).

Cuba: Is found with Eleocharisinterstincta along the middle vegetation zone (defined by fluctuating water levels) of the Santa Cruz Reservoir (Fraga and Quesada, 1995).

Disturbed Areas

Egypt: In canals and ditches of the Mediterranean region of the Nile Delta, P. geminatum grew with Atriplex and Chenopodium along the banks and slopes, with Phragmites and Juncus emerging from the littoral zones, and with Lemna and Potamogeton in deeper waters (Shaltout et al., 1995).

Pakistan: Found along polluted, urban rivers and waste effluents with the weedy alien Prosopis juliflora and the overly abundant, native annual sandspur Cenchrus barbatus [=C. biflorous] (Muhammad et al., 2008).   

Mexico: P. geminatum is listed with 29 other native taxa as problematic in the canals in Mexico. Only 3-4 of these species are introduced (Gomez Mendez, 2000).

Faunal Associations

Offshore communities of P. geminatum provide a highly favorable structure for the establishment of benthic periphyton and macroinvertebrates and, even more importantly, the vertical distribution of epiphyton and their associated macroinvertebrates, which are eaten by fish (Schramm and Jirka, 1989).

Climate

Water Tolerances

Notes on Natural Enemies

In lakes of the Kissimmee River, Florida, USA, the integrity and open structure of offshore beds of P. geminatum appear under threat from overgrowth by Ludwigia hexapetala, an invasive primrosewillow (Jacono, pers. obs.).

Means of Movement and Dispersal

P. geminatum can spread by seed or by clones, using the latter particularly at disturbed sites. It is adept at colonizing compacted and denuded soils from stem pieces (Pouder et al., 2006). Fragments of both emergent and decumbent stems are inadvertently cut and buried by the digging, shifting and ploughing of engineering and maintenance machinery.

P. geminatum can spread through irrigation canals, open waste ditches and polluted riparian systems.

Impact Summary

Impact

In all cases reviewed herein, problems caused by P. geminatum were apparently the result of environmental disturbances by human intervention rather than its introduction as an alien species. Indeed, P. geminatum is not on alert or regulated pest species lists. In Florida, USA, it is routinely protected during management practices and propagated on a large scale for habitat enhancement and lake restoration (see Environmental Services).

Competitive biological characteristics, such as monopolizing resources or shading associates (see Risk and Impact Factors Summary Table: Impact Outcomes), have not been demonstrated with P. geminatum.

Economic Impact

By its rheophytic nature, P. geminatum has been recorded as contributing to the blockage of smaller streams in west Africa (Burkill, 1985). Its primary negative impact, however, occurs in arid and warm temperate zones, such as in Egypt, Pakistan and Mexico, where it can spread through irrigation canals, open waste ditches and polluted riparian systems. In these situations, extensive biomass produced can compromise water flow and flood control (Shaltout et al., 1995).

Risk and Impact Factors

• Invasive in its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Capable of securing and ingesting a wide range of food
• Highly mobile locally
• Benefits from human association (i.e. it is a human commensal)
• Long lived
• Fast growing
• Gregarious
• Has propagules that can remain viable for more than one year
• Reproduces asexually

• Increases vulnerability to invasions
• Monoculture formation
• Negatively impacts agriculture
• Soil accretion

• Filtration
• Rapid growth
• Rooting

Uses

Economic Value

Naturally occurring stands of P. geminatum are well recognized as useful wild pasture for livestock. As reported from Senegal, Nigeria, Somalia, Uganda, and India it is enjoyed by nearly all types of livestock, the succulent culms probably adding to its palatability (Burkill, 1985). The species has been noted as especially important before the start of the rainy season in the upper Ganges basin of India, after standing water has been replaced by low-lying meadows favoured for cattle and pig grazing (Misra, 1976). More recently in Sri Lanka, P. geminatum was highlighted, along with six other naturally occurring grass species, for its ability to maintain dominance under brackish marsh environments; it is therefore expected to become more important as rising sea levels and associated tides increase salinity farther inland (Premaratne and Premalal, 2008).

Social Benefit

P. geminatum is traditionally used by the Seminole Indians of southern Florida as a dermatological aid. A decoction of the whole plant was taken and used as a body steam for the skin problem ‘snake sickness’. It was also used as a remedy for itchy skin (Sturtevan, 1954, as cited in Moerman, 2013). This traditional Native American use may still be employed in the Everglades region today.

Burkill (1985) found no record of the seed of P. geminatum being collected for human use, although he speculated that its seed also may be edible. In India the seed of P. flavidum is collected as a famine food.

Environmental Services

P. geminatum functions as a primary coloniser of newly flooded lake beds, forming broad, emergent zones that quickly act as wave buffers and allow other species to establish, for example in Tanzania (Welsh and Denny, 1978) and Florida (Pouder et al., 2006).

P. geminatum can also create an offshore habitat for fish and aquatic fauna. Even in nutrient-enriched lake waters, P. geminatum maintains a more open benthic and littoral community with a type of structural complexity that supports and distributes periphyton and epiphytic macroinvertebrates vertically through the water column.

In areas of the Nyumba ya Mungu reservoir, Tanzania, that were dominated by P. geminatum, the occurrence of major shoals of commercial fishes (Sarotherodonpangani and S. jipe) correlated with their habit of feeding on periphytic algae (Bailey et al., 1978; Bowker and Denny, 1978). Studies in Florida revealed similar findings. In large lakes of central Florida, Schramm and Jirka (1989) found that the open, intermediate density of underwater stems produced by P. geminatum supported epiphyton at numbers and diversities that much exceeded those found with other aquatic plants. Welch (2009) also found P. geminatum to offer especially productive habitat for freshwater fish favoured by anglers in Lake Tohopekaliga, Florida.

Wildlife Food and Habitat

P. geminatum is grazed on by a variety of animals, including hippopotamus (Lock, 1973). Elephants have been observed freely grazing on the floating mat habitats created by P. geminatum along the lake margins of the upper Ganges (Misra, 1976).

Grasses and sedge marshes supported by P. geminatum provide the only known overwintering ground for the Siberian crane (Grus leucogeranus) on the Indian subcontinent, at Keoladeo Ghana Bird Sanctuary. The habitat supports an enormous avian fauna (Gopal, 1994).

Lake Restoration

In natural areas around the world, emergent stands of P. geminatum are highly desired for their use in ecosystem management. It is particularly well adapted to quick regrowth on land re-flooded after a dry period and is valued for controlling erosion and as an indicator of water quality (for example in Peru; Leon et al., 1977).

It has been employed routinely since 1976 to restore or improve degraded aquatic habitats in eutrophic lakes in Florida.

Restoration management entails two methods of propagation: 1) growing tips and stem fragments, and 2) whole plants. Stem regeneration should be consistently more successful at lower elevations where stems were buried closer to the water’s edge (Pouder et al., 2006). To collect stem fragments, cutting at a depth of 30 to 70 cm below the water surface was achieved with a mechanical aquatic harvester (Kelpin 800, 21.3 m harvester) (Mallison et al., 2006). Harvesting had a minimal, short term effect on offshore populations. Within three weeks, emergent regrowth of the source plants had advanced to equal that of pre-harvest densities (Mallison et al., 2006). Transplants or stem fragments are planted to a water depth of 2.5 m following herbicide treatment or drawdown and scouring for dirt removal (Mallison and Thompson, 2010).

Detection and Inspection

Separating P. geminatum from other tribes of grasses:

P. geminatum is perennial, does not form a winter rosette, and its basal leaves do not differ from stem leaves.  The infloresence consists of several spike-like racemes along a main axis; rachis of racemes somewhat flattened, ending in a short, naked point (not a bristle); spikelets glabrous, fruits transversely rugose.

Separating P. geminatum from other Panicum in the tribe Geminata:

P. geminatum is glabrous throughout, nodes glabrous. Spikelets to 3.3 mm; glumes and sterile lemma not papery.

Determining P. geminatum:

The ligule is a ring of hairs to 1 mm long. Leaf sheaths compressed. Leaf blades flat medially, linear, the long-tapering tips involute; blades mostly glabrous or with minute hairs at base of upper surface. Infloresence up to 30 cm long and bearing 6 to 20 alternating, short-ascending or appressed-ascending flattish, spike-like fertile branches. The rachis is sharply 3-angled and ends in a short naked point, not a bristle.  Spikelets planoconvex or nearly so, 2.2 to 3.3 mm long, arranged alternately in two rows on one side of the sharply 3-angled rachis. Spikelets are ovate to oblong-elliptic in shape. The first glume is short, as broad as it is long or broader than it is long.

Similarities to Other Species/Conditions

Paspalidium obtusifolium is overall smaller and stouter in stature than P. geminatum yet grows in similar soils and semi-permanent wet habitats, commonly with mixed graminoids.  Its culms are shorter, leaf sheaths wider and loose, leaf blades shorter and wider with tips quickly terminating in a wide, blunt tip, and its panicles wider than P. geminatum. P. obtusifolium has been reported as behaving like a weed in Morocco (Holm et al., 1979).

P. flavidum (syn. Panicum flavidum) is common as a weed in Philippines, Cambodia, Mauritius and Vietnam, and is also present in Burma and India but lacking evidence of weediness there (Holm et al., 1979). In determining the species of Paspalidium in central India, Deshpande and Singh (1986) distinguish P. flavidum by the relative length of the inflorescence and separate P. punctatum from P. geminatum by the relative length of the upper glume, where spikes shorter than internodes indicates P. flavidum, and spikes longer than the internodes indicates either P. punctatum (if the upper glume is half the length of the upper rugulose lemma) or P. gemiatum (if the upper glume is nearly half as long as the upper granular lemma).

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Chemical Control

Herbicides are currently the only method for control. Koschnick et al. (2007) found that the shoot biomass of P. geminatum was inhibited by the acetolactate synthase (ALS)-inhibitors bispyribac and penoxsulam at concentrations of 75 µg/litre and higher when compared to untreated controls. Glyphosate is recommended for control in Mauritius, but a high dose of 5-6 kg/ha is needed (Mauritius Sugar Industry Research Institute, 2004).

Gaps in Knowledge/Research Needs

A thorough review of monographic literature and specimen vouchers will be necessary to better understand the plant’s status as native or introduced in the disjointed distributions in southern Africa.

Molecular analysis could be undertaken to investigate the genetic variability between weedy populations in arid and warm temperate regions and more naturalistic populations in tropical and more humid regions.

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Links to Websites

Contributors

12/02/14 Original text by:

Colette Jacono, University of Florida, USA

Distribution Maps