Cyperus papyrus (papyrus)

Sudd mats as well as young floating papyrus mats can form and be dispersed by wind and wave action; they then may join existing mature stands elsewhere or establish new populations along formerly unoccupied shorelines (Osborne, 2012; Terer et al., 2014, 2015).

Most long-distance transport of this species, either as entire plants or as seed, has indubitably been by human activity, although the dispersal of seeds attached to the feet or plumage of water birds is possible and may account for dispersal from one water body to another (Rooney, 2013).

Escape from introduced populations is quite possible, especially if small populations in botanical and domestic gardens are not adequately contained and garden waste is disposed of improperly.

This method of spread is the most likely, both from one country to another and within a country. C. papyrus has been introduced to and is popular as a showy ornamental pond plant in several countries and its further spread in this way is bound to continue.

The chromosome number of C. papyrus is 2n = 102 (Vaughan, 2011). Triest et al. (2013) found that the C. papyrus swamps of Lake Naivasha in Kenya are highly diverse in clones, suggesting that mature stands there all originated through seedling recruitment, apparently from seed rain at short distances. Once formed, mature populations maintain their high levels of diversity by local vegetative growth. Close relationship and infinite gene flow were found between seedlings on the shoreline and the nearest part of the C. papyrus belt. Using microsatellite markers to assess clonal diversity, genetic variation and genetic structure, Terer et al. (2015) revealed strong isolation by distance among C. papyrus populations in the Rift Valley lakes, Lake Victoria and isolated wetlands of Kenya, and the maintenance of relatively high levels of clonal and gene diversity at the species level.

C. papyrus is known to be adapted to normal climatic cycles of drying-flooding and exhibits both sexual reproduction and unlimited clonal propagation. Young floating papyrus mats can detach from the shoreline to be dispersed by wind and wave action; they then may join existing mature stands elsewhere or establish new populations along formerly unoccupied shorelines (Terer et al., 2014).

When Boar (2006) studied the germination of seeds of C. papyrus taken from stands in Lake Naivasha, she found that seeds germinated and seedlings survived best when lake sediment was saturated or the water level was just below the sediment surface. Seeds germinated and seedlings survived poorly in sediment that was drying and seeds did not germinate at all when the sediment was flooded. Observations from field and germination experiments led Boar (2006) to suggest that papyrus seeds germinate quickly in rewetted sediment but that new swamps will only form on shallow gradient shores or when water level is rising slowly enough for seedling growth to keep pace with water level.

Champion and Hofstra (2014) note that in New Zealand C. papyrus probably reproduces only by spread through layering; although seed is occasionally produced its viability has not yet been positively determined. It must, therefore, be dispersed by deliberate planting or garden discards, although some occurrences in very remote situations are difficult to explain if they only originated from garden discards.

The stems of C. papyrus have a fibrous green outer skin which surrounds a soft white pith composed of parenchyma cells surrounding hollow air ducts and rigid fibrovascular bundles. The air ducts contribute to stem buoyancy and are also involved in CO₂ recycling within the plant. A mature papyrus plant consists of stems of different maturity, all arising from the same rhizome. Stems first elongate from this base with their umbel partially closed until they reach full height, at which point the umbel opens fully. Eventually mature stems senesce and die, leaving only a dry broken stump. The time from emergence of a new stem to death of that stem has been measured at 147 days in Lake George (Uganda). The plant normally has no functioning leaves, instead carrying out photosynthesis through the green epidermal layer of culms and sterile umbel inflorescences. The true leaves that accompany the early emergence and extension of new stems senesce under a mature canopy due to lack of light penetration to the plant base. These leaves only serve as photosynthesizing organs during regrowth after cutting or burning of a papyrus stand, or in areas newly colonized by papyrus plants. In southern Africa flowering is in November–March (Vaughan, 2011).

In its native environment, papyrus grows year-round with rapid uptake of nutrients and accumulation of biomass. Dead plants sink to anaerobic layers of the swamp and form a mass of peat which oxidises to release carbon dioxide when the water level falls again (Vaughan, 2011). In cooler countries to which the species has been introduced, although frosts can kill the aerial parts of the plant, in the following spring it will regrow from the base (Archer, 2004).

C. papyrus has C₄-photosynthesis, which contributes to its exceptionally high productivity. Growth rates of up to about 40 g/m² dry weight per day have been recorded in natural swamps, resulting in a theoretical annual production of up to 145 t dry matter per ha; however, in a constructed wetland in Uganda the annual production was 240 t per ha. In hydroponic culture short-term growth rates of up to 125 g/m² dry weight per day are possible. In Lake Naivasha the total standing biomass was found to be 78 t dry matter per ha. Of this total biomass, 57% was located in the rhizome, 1% in the roots, 29% in the stems and 13% in the umbels (Vaughan, 2011).

Gaudet (1977b) found that C. papyrus was the most adaptable of the plant species in Lake Naivasha, starting from seed on bare mud in competition with hygrophilous annuals and later growing up in water as a perennial emergent macrophyte. Lake Naivasha, in common with other freshwater lakes in tropical East Africa, shows both seasonal and longer-term fluctuations in water level. Terer et al. (2014) documented seed production, seedling recruitment, zonation progression, and dispersal of seed of C. papyrus in Lake Naivasha. In five umbels they estimated seed numbers to be between 98,000 and 337,000. As the lake dried out, desiccation and cracking of the mudflat soils occurred, along with oxidation and demise of littoral aquatic plants. When the lake water level rose again, distinct zones of young plants of C. papyrus and hygrophilous ephemerals developed. The authors observed C. papyrus seedling densities of between zero in the parent papyrus zone and 186 m^-2 in the ‘sedge zone’. When the lake water reached its normal high levels, hygrophilous ephemerals died off while C. papyrus survived.

No reports seem to be available on the longevity of individual plants of papyrus but presumably since they seem to be able to reproduce indefinitely by vegetative means some of the clonal plants now found in permanent lakes and rivers in Africa may be exactly the same plants that were present hundreds of years ago.

Van Dam et al. (2011), quoting Gaudet (1977a), Jones and Muthuri (1997) and Saunders et al. (2007), say that culm densities range from less than 10 to over 22 shoots m^-2, leaving little room for other plants, although climbers such as Ipomoea spp. are found growing amongst it.

In most African permanent wetlands C. papyrus is the dominant species. It has been estimated that monotypic and mixed papyrus swamps cover 40,000 km² in Central and East Africa, although the extent of many local papyrus swamps there has diminished as a result of drainage and infilling for cultivation and construction (Vaughan, 2011). In Lake Naivasha, for example, the area of C. papyrus swamp declined from 45 km² in 1960 to 6 km² in 2001 (Hickley et al., 2004). This decline is attributed to water level fluctuations, land clearance and decimation of submerged vegetation by the introduced alien crayfish Procambarus clarkii (Osborne, 2012).

Additional information on clonal structure and the size of C. papyrus clones in Kenya can be found in Terer et al. (2015).

The aerial biomass of C. papyrus shows a positive response to higher nutrient conditions in wetlands receiving domestic wastewater (Kipkemboi et al., 2002).

According to Gaudet (1977b), the species most commonly associated with mature swamps of C. papyrus in East Africa are other species of Cyperus, species of Polygonum, Melanthera scandens subsp. madagascariensis, Ceratophyllumdemersum, Lemnatrisulca, Salviniamolesta and Wolffiaarrhiza.

C. papyrus is the principal species of the sudd communities of Lake Naivasha and elsewhere. The term sudd refers to mats of floating vegetation, first applied to the massive C. papyrus mats that developed in wetlands adjacent to the upper Nile in Sudan. Sudd mats form as rhizomes of C. papyrus and the floating stems of aquatic plants such as Vossia cuspidata and Ludwigia spp. become intertwined. The mat may be further colonized by plants such as Impatiens and Aeschynomene spp., as well as sedges and aquatic grasses (Osborne, 2012).

Zohary (1962) reported on the association of C. papyrus and Polygonum acuminatum [Persicaria acuminata] which used to occupy large stretches of the flooded peat soils of the Huleh swamps in the northern Jordan Rift Valley on the border between Syria and Israel. The swamps were later drained and much of the vegetation destroyed. However, Kaplan et al. (1988) describe the re-flooding of parts of the area in the 1990s and the successful re-colonization with C. papyrus, both spontaneously and through transplants.

Duke (1983) says that C. papyrus requires annual rainfall of 10-420 cm, annual temperatures of 20–30^oC and a pH of 6.0–8.5. On the Highveld of South Africa, plants of C. papyrus can apparently tolerate a few degrees of frost. The plants are more or less dormant in winter and as long as the rhizomes are protected from freezing the old culms will be replaced by new ones in the spring (Archer, 2004). Kew Seed Information Database (2015) describes the species as a hydrohalophyte, although the species is exclusively a freshwater species. 

C. papyrus has potentially serious impacts on environments in countries to which it has been introduced, with its propensity for forming monotypic stands on the margins of lakes and rivers. Floating islands of the species can float downstream and seeds may be spread by water birds to new areas. Such invasions could disturb the ecological balances of wetland environments and displace native species. It is already of concern in Queensland and northern New South Wales in Australia, although it is, as yet, only considered a minor environmental weed. Having escaped from cultivation, it has invaded the margins of permanent water bodies in southeastern Queensland and northern New South Wales, including in the latter case the Seaham Swamp Nature Reserve at Port Stephens on the mid-north coast. It is also a weed of deep water channels in the Warriewood Wetlands and a common weed in the Lakes of Cherrybrook Reserve in suburban northern Sydney. In south-western Western Australia it grows in permanently wet sites and in abandoned parklands. This rapidly growing species can spread to cover areas of open water, preventing other aquatic species from growing, and reducing light levels to submerged native plants (Queensland Government, 2015).

In Hawaii, C. papyrus has been found as an abundant and naturalized alien in several national parks, including the Waimanu National Estuarine Sanctuary on Hawaii (State of Hawaii, 1984), the Nounou Forest Reserve on Kauai (State of Hawaii, 2015) and the Kawai Nui Marsh on Oahu, Hawaii’s largest remaining wetland, covering 335 hectares, and an important habitat for endangered native waterbirds as well as migratory birds; C. papyrus has been identified as invasive here, forming several dense stands (US Army Corps of Engineers, 2008).

In Zambia, where C. papyrus is considered by some as an alien invasive species, it is of concern in the Kafue River flats where it is spreading rapidly, endangering native plant species and the value of the flats as a habitat for birds (Zambian Alien Invasive Species, 2014).

In Mexico, C. papyrus was identified as one of several aquatic weeds which, although not having a wide territorial distribution, had invaded large areas in several aquatic ecosystems (Bonilla-Barbosa, 2013).

Little is known of the potential effects of C. papyrus on biodiversity where it has been introduced but its growth form and biology are so different from those of other aquatic plants that it would be bound to have major disruptive effects on native biodiversity. In Australia, it can crowd out other aquatic plants and can reduce light levels reaching submerged native plants (Queensland Government, 2015).

Duke (1983) notes that C. papyrus was used in Egypt as early as 2400 BC for food, medicine, fibre and shelter. He quotes Täckholm and Drar (1950) in listing a very comprehensive range of uses to which the species was put in ancient Egypt, including funeral garlands, boats, cordage, fans, sandals, mattings, corkage, boxes and paper. The pith was used as food, while the starchy rhizomes and lower part of the stems were cut off and consumed raw, boiled or roasted. Ironically, C. papyrus is now thought to be extinct in the lower Nile marshes, presumably due to over-harvesting through the millennia.

Zohary (1962) lists C. papyrus as one of the native swamp plants that the Arabs in southern Palestine used as the basis for their wickerwork and mat industries.

In modern times, Lake Victoria wetlands, whose dominant species is C. papyrus, constitute a vital life support system for about 12 million people who extract fresh water, fish, medicinal plants and building materials (Raburu et al., 2012). Morrison et al. (2012) compiled a long list of the socioeconomic services of papyrus, which included fodder for livestock, use for brooms and decoration, as fuel, for making fish traps, cooking utensils, granaries, walls and furniture, thatch, ropes, hats and boxes, mats, window blinds, celling board, as a herb for cooking and as a medicine for various ailments. However, they and other authors have cast doubts on the sustainability of current practices of utilization by local populations around, for example, Lake Victoria; threats to papyrus swamps include rising human population pressures, drainage of swamps for agriculture, perpetual harvesting, poor management systems, lowering of lake levels by over-extraction of water leading to damage by large mammals, and a changing climate. Kiwango and Wolanski (2008) concluded their study by reporting that the future state of Lake Victoria and the welfare of its human population are highly related to the future of its papyrus wetlands. Methods of conserving this valuable resource for local economies have been proposed. Terer et al. (2012) recommended a harvesting regime that allowed an adequate period for a full cycle of stems from young to senescence, of at least 12 months.

In its native environment in tropical Africa, C. papyrus swamps are an important habitat supporting a wide diversity of species, notably populations of sitatunga antelope (Tragelaphus spekii), African python (Python sebae), several birds with restricted distributions including the papyrus yellow warbler (Chloropeta glacilirostris), and the papyrus gonolek (Laniarius mufumbiri). The swamps provide breeding and feeding grounds for numerous species of fish, as well as grazing for large herbivores (Mnaya and Wolanski, 2002; Owino and Ryan, 2006; Terer, 2011).

Mwaura and Widdowson (1992) established that nitrogen fixation occurs in the intact root systems of C. papyrus and nitrogen fixation associated with young roots could provide 26% of the nitrogen requirements of growing papyrus plants. This nitrogen fixation was thought to be due to the presence of diazotrophs in the root zone of the papyrus plant.

Apart from major biodiversity and ecological ecosystem services, a wide range of regulatory ecosystem services are provided by C. papyrus swamps, services in relation to water, carbon and nitrogen cycles and buffering capacity for sediment and nutrient loads, as well as a huge range of services in respect of natural products of benefit to communities, including biofuels, drinking water, building materials and flood control (Gichuki et al., 2001; Saunders et al., 2007; Maclean et al., 2011; Van Dam et al., 2011). Some modern uses mooted for C. papyrus include as a biofuel and as a part of filtration systems for removing sediments, sewage and heavy metals from polluted water (Gaudet, 2014). Dry matter productivity is very high, especially as it can come from otherwise unused aquatic environments (Rooney, 2013).

Another important role for C. papyrus is the assimilation and sequestration of significant amounts of carbon dioxide from the atmosphere. Saunders et al. (2014) estimated that up to 80 t C ha^-1 is stored in above- and below-ground components of vegetation and, under flooded conditions, a further 640 t C ha^-1 may be stored in detritus and peat deposits. Gichuki et al. (2005) found that carbon derived from papyrus is largely retained in papyrus swamps; additionally high mineralization of organic matter occurs in the swamp, indicating that the retained papyrus-derived carbon is largely respired.

The best way to prevent C. papyrus from spreading is to prevent its introduction from other ecosystems, to detect incipient infestation at an early stage and to implement an effective eradication programme before the plant begins to spread to other wetland areas. In the case of Zambia, for example, it is recognised that there is a need to regulate, restrict, limit or prohibit the importation of a variety or class of seeds suspected of being from a weed, like papyrus. This is provided for by the Plant Variety and Seed Act, 1970, in the Laws of Zambia (Zambian Alien Invasive Species, 2014).

According to Zambian Alien Invasive Species (2014), cutting and raking of the cut materials can be an ideal method of dealing with the nuisance of papyrus, and this can either be done with sickles or specialized and powered mechanical cutters. The material thus cut can then be removed, hand raked, drag-lined or removed with motor driven elevators. The cut materials can serve as fodder for pigs and rabbits.

In Kisumu in Kenya in the late 1960s, floating rafts of C. papyrus would sometimes be piled up by wind and waves around the dock area and, so the story went, they were cleared by prisoners from the local jail in spite of the rafts being infested with snakes (Ian Popay, personal observation, 2014).

Zambian Alien Invasive Species (2014) claims that “biological control of papyrus can be achieved by the production of toxin from a novel fungal isolate. The novel isolate, Dactylaria higginsii [Pseudopyricularia higginsii], can be grown, and the toxins recovered by the techniques which are well known to those skilled in the art. The fungus can be used to directly and specifically deliver its phytotoxin composition to papyrus. This is delivered to the plant by applying an effective amount of the biologically-active fungus directly to the plant. The fungus produces sufficient quantities of a phytotoxin compound to inhibit the growth, or actually induce mortality of papyrus. The growth of the fungus can also mechanically disrupt nutrient transport in the vascular system of the plant.” This material has been developed as a bioherbicide for the control of weedy sedges like purple nutsedge (Cyperus rotundus) (Kadir and Charudattan, 2000) but there seems to be no confirmed evidence of its effectiveness on C. papyrus.

According to Zambian Alien Invasive Species (2014), herbicides which show success in the control of C. papyrus include glyphosate and soil fumigants; the success or failure of herbicide treatments depends on the growth stage of the plant at the time of application, soil moisture and temperature.