Melinis repens -- California

Natal grass is native to southern Africa. It is very widely naturalized in Australia and most abundant in the northern and eastern parts of the country. It is common in Queensland, the Northern Territory and eastern New South Wales and scattered in other parts of New South Wales, in southern Victoria, in northern and south-western Western Australia and some parts of South Australia. Also naturalised on Norfolk Island and Christmas Island. Widely naturalized elsewhere in the world, most or all of the Central American countries (Panama through Guatamala), Ecuador, Peru, Columbia, Singapore, Taiwan, China, the southern USA (i.e. California, Arizona, New Mexico, Texas, Louisiana, Florida, Georgia and North Carolina) and on several Pacific islands (i.e. the Cook Islands, Fiji, French Polynesia, Guam, Kiribati, Nauru, New Caledonia, the Solomon Islands) and Hawaii (Weeds of Australia Biosecurity Queensland Edition) .

Naturalized in coastal California and the San Joaquin Valley (Jepson e-Flora). Widely naturalized in Australia, and most abundant in the northern and eastern parts of the country. It is common in Queensland, the Northern Territory and eastern New South Wales and scattered in other parts of New South Wales, in southern Victoria, in northern and south-western Western Australia and some parts of South Australia. Also naturalised on Norfolk Island and Christmas Island. Widely naturalised elsewhere in the world, including southern USA (i.e. California, Arizona, New Mexico, Texas, Louisiana, Florida, Georgia and North Carolina) and on several Pacific islands (i.e. the Cook Islands, Fiji, French Polynesia, Guam, Kiribati, Nauru, New Caledonia, the Solomon Islands and Hawaii (Weeds of Australia Biosecurity Queensland Edition). Its distribution overlaps with more than 50% of California Hardiness Zones (Cal-IPC global map of climate areas matching California).

A very common weed of roadsides, railways, parks, gardens, footpaths, disturbed sites, waste areas, pastures and crops in tropical and sub-tropical regions. Also present in temperate, semi-arid and arid areas. Natal grass is a grass native to southern Africa that has become a problematic weed in many tropical and subtropical regions around the world, including Florida, Mexico, the Caribbean, Central America, Brazil, and many Pacific islands, Australia (New South Wales, Queensland and Western Australia) Dominican Republic and French Polynesia (CABI). In Florida, Natal grass exists in many areas but is particularly widespread in the southern pine rocklands and central part of the state (David and Menges 2011), where it is documented to have spread from roadsides into intact habitat (USDA 2011). It is listed by the Florida Exotic Pest Plant Council as a Category I invasive (FLEPPC 2015). Although considered a weed in many countries, it is not currently regulated. Natal grass is regarded as an environmental weed in Queensland, New South Wales, Western Australia and the Northern Territory and was also recently listed as a priority environmental weed in at least one Natural Resource Management region (Weeds of Australia Biosecurity Queensland Edition).

Melinis repens is mainly considered invasive in natural grasslands and shrublands and is considered a very common weed of roadsides, railways, parks, gardens, footpaths, disturbed sites, waste areas, pastures and crops in tropical and sub-tropical regions. Holm et al. (1979) list it as a ‘serious’ weed in Australia, Brazil and Ghana, and ‘principal’ in Malaysia and Zambia. It is considered to be invasive in parts of Texas, southern California, Mexico, Queensland, New South Wales, and Western Australia that match California's climate. It is also considered invasive in many other areas that do not match, including Florida, Hawaii, the Dominican Republic and French Polynesia (CABI). Natal grass also occurs in temperate, semi-arid and arid areas. Red Natal grass (Melinis repens) is formally regarded as an environmental weed in Queensland, New South Wales, Western Australia and the Northern Territory. It was also recently listed as a priority environmental weed in at least one Natural Resource Management region (Weeds of Australia Biosecurity Queensland Edition).

Melinis minutiflora in Brazil (Zones 9b-13); Melinis nerviglumis in Madagascar, Africa Sub Saharan South Africa, Zones 8a-11 (GCW), both of which overlap substantially with California's Zones (5a-11) (GCW WRA). However, per personal communication with Joseph DiTomaso, "I would answer a NO to this question. Melinis minutiflora is pretty much only a tropical grass." As such, this is scored a 'No'. Melinis nerviglumis is sold occasionally as a landscape ornamental in California, but there is no evidence that it has naturalized to date (R. Vanderhoff, personal communication).

Ecology: Disturbed areas, slopes; Elevation: < 850 m. Bioregional Distribution in California: NCoRO, SnJV, s CCo, SCoRO, SCo, WTR, PR (Jepson). Melinis repens is invasive in Southern California, Texas, Florida and Hawaii (Lawn begone). It is known to be invasive in Mexico, USA (California, Florida and Hawaii), Australia (New South Wales, Queensland and Western Australia) Dominican Republic and French Polynesia (CABI). Widely recorded in South America and Asia, including in many areas that do not match California's climate. Appears to inhabit some tropical and temperate climates, in addition to subtropical. Grows best in USDA Hardiness Zones 10a-11 (Dave's Garden).

Found in disturbed open places, often forming large stands (Flora of Zimbabwe). This species will compete with and displace native species (Possley and Maschinski 2006). In the USA, this species invades undisturbed pine rocklands in Florida (Stokes et al., 2011) and invades coastal grasslands dominated by Heteropogon contortus in Hawaii. In Sonora, Mexico it is replacing native grasses in desert grasslands including unique grassland with feather trees (Lysiloma watsonii). It is also growing in disturbed openings in tropical deciduous forests in eastern Sonora (Van Devender and Reina, 2005). Found to be an intermediate competitor with other grasses in an Arizona experiment, M. repens was better able to tolerate resource depletion by buffel grass (Pennisetum ciliare), than the native Arizona cottontop (Digitaria californica), giving it a competitive edge over the native species (Stevens and Fehmi, 2009). Rare plant species on Brazilian inselbergs are threatened by the spread of M. repens (Porembski et al., 1998). Six Hawaiian species growing on Lanai and/or Maui are threatened by M. repens because of its impact on fire frequency. Stands of M. repens can increase the number of fires; negatively affecting the growth and survival of other native flora and fauna (La Rosa et al., 2008 - CABI). Displaces native vegetation and prevents the natural succession of native species (FloraBase—the Western Australian Flora). It is a primary invader of abandoned crop fields and unimproved pastures and prevents the natural succession of native species such as Andropogon and desirable forbs in Florida (University of Florida IFAS Extension). Natalgrass competes with native plants for nutrients, light, water and space, and prevents colonization by native species. In fact, its invasive potential was noted early on when Tracy (1916) reported its value as a “smother crop,” which “makes such vigorous growth as to choke out most other grasses and weeds.” (Southeast Exotic Pest Plant Council, SE-EPPC). M. repens density class was strongly associated with a reduction in native species diversity, with high density (20% cover) plots having five fewer species than low density (0.2%) ones. When we separated species by functional groups, we found that graminoids were affected much more than other native species, with M. repens cover explaining 23% of the variation in graminoid diversity (Possley and Maschinski, 2006). In San Diego County, California, there are numerous records of M. repens dominating a site and presumably displacing native plant species (e.g., Vanderhoff 2015: https://www.calflora.org/entry/occdetail.html?seq_num=po8507).

The dry biomass of the plant leads to an increase in fire frequencies and its dense growth crowds out native early successional species (CABI). Stands of M. repens can increase the number of fires; negatively affecting the growth and survival of other native flora and fauna (USDA 2011). Six Hawaiian species growing on Lanai and/or Maui are threatened by M. repens because of its impact on fire frequency (La Rosa et al., 2008). "...[I]n dry areas and scrub habitats that historically supported discontinuous grass cover mixed with shrubs, natal grass creates continuous fine surface fuels unlike those in natural stands" (USDA 2011). Fire does not offer long-term control, and may actually provide an advantage by creating disturbed areas that are quickly colonized from seed (Southeast Exotic Pest Plant Council, SE-EPPC). Natal grass is also tolerant of fire and establishes easily in burned areas (USDA 2011).

Cattle and sheep eat M. repens but have not been used to control it (CABI). The pollen is a mild allergen (Landscape Plants for South Florida). An exhaustive Google/Google Scholar search did not additional reveal information about health hazards or toxicities.

Found in disturbed open places, often forming large stands (Flora of Zimbabwe). Natalgrass forms tussocks that grow up to 1 m in height (Seed Biology and Ecology of Natalgrass (Melinis repens)). An exhaustive Google/Google Scholar search did not reveal additional information about formation of thickets of slowing/blocking of movement, although the potential height of this plant makes it possible. This question defaults to a "No" at this time.

Although this species does not produce rhizomes, it can root at the nodes and sometimes develops a sprawling appearance (Haselwood and Motter 1966, cited in Stokes et al., 2011). Can be propagated by division (Dave's Garden), although this does not warrant a classification of natural "vegetative" propagation; however, the "layering" capability of this plant does. However, per personal communication with Joseph DiTomaso, "I have never seen this plant reproduce vegetatively. It is a bunchgrass and I do not believe that spread is due to vegetative growth, so it is pretty much a perennial that reproduces by seeds." As such, this is scored a 'No'.

An exhaustive Google/Google Scholar search did not reveal information about production of new plants by fragmentation. Per personal communication with Joseph DiTomaso, this should be answered a 'No' and not left blank.

Natal grass is a prolific producer of windborne seeds. Tracy (1916) suggests that 45.4 kg (100 lb) of seeds per 0.4 ha(1 acre) could be expected from the initial growth of a natal grass crop. In areas where severe natal grass infestations occur, dense layers of seeds up to 5 cm thick have been observed on the soil surface (C. A. Stokes, unpublished data). Natal grass seeds appear to be key to the rapid spread of this species, and extensive seed deposits are likely a reason for the persistence of natal grass in a given area (Stokes et al., 2011).

Díaz Romo et al. (2012) measured up to 3,906 seed/m2 in Mexico (CABI). Natal grass is a prolific producer of windborne seeds. Tracy (1916) suggests that 45.4 kg (100 lb) of seeds per 0.4 ha(1 acre) could be expected from the initial growth of a natal grass crop. In areas where severe natal grass infestations occur, dense layers of seeds up to 5 cm thick have been observed on the soil surface (see Stokes et al., 2011).

Most natal grass germination occurs at temperatures higher than 15 C and in conditions with adequate moisture available. Natalgrass appears to require an after ripening period following seed shed to reach maximum germination potential. Although natalgrass can form dense seed deposits in infested areas, the seed bank appears to quickly become depleted when conditions are favorable for germination and further seed rain is prevented. Seeds can remain viable in the soil for up to a year but once adequate moisture and temperature conditions are reached nearly all seeds germinate. Seed collected from the duff layer had an initial germination rate of 49% ± 3.8%, while seed collected directly from seedheads had a germination rate of 6% ± 5.1% (Stokes et al, 2011). Seeds do not germinate well when first shed, but after an after-ripening period, germinate in less than 24 hours when exposed to water (Southeast Exotic Pest Plant Council (SE-EPPC)). Seeds can germinate with adequate moisture, although they do require an unspecified after-ripening period. This question remains unanswered at this time.

In California is an annual or short-lived perennial (Jepson). Natal grass is an annual species that sometimes perennates in warmer climates (Hafliger and Scholz 1980; Haselwood and Motter 1966; Kleinschmidt and Johnson 1977). Although its native range in south and east Africa has a warm climate, these regions experience seasonal dry conditions and heavy grazing pressure from animals, which migrate at certain times of the year, causing plant dieback (Klages 1942). In Florida, Natal grass will sometimes perennate in those areas of the state that do not experience freezing temperatures (MacDonald et al. 2008). [All references cited in Stokes et al, 2011]

Blooms year-round in California (Calflora; Jepson). In Zimbabwe, Sep - Jun (Flora of Zimbabwe).

Watershed Health (2007) reports that M. repens (aka Rhynchelytrum repens) is spread by wildlife. The light, fluffy seeds of natal grass are, according to "Weeds of Australia", often wind-dispersed and may also become lodged in clothing, vehicles and animals. Seeds can also be spread in mud and contaminated agricultural produce (i.e. fodder and pasture seed) (Queensland Government 2011).

Seed is distributed by wind and establishes readily along roadways, coastal sage and grasslands primarily in coastal areas and foothills (Watershed Health 2007). Some seeds have been discovered in seed shipments (CABI). Red Natal grass (Melinis repens) reproduces mainly by seed. These light and fluffy seeds are often wind-dispersed and may also become lodged in clothing, vehicles and animals. Seeds can also be spread in mud and contaminated agricultural produce (i.e. fodder and pasture seed) (Weeds of Australia Biosecurity Queensland Edition).

Red Natal grass (Melinis repens) reproduces mainly by seed. These light and fluffy seeds are often wind-dispersed and may also become lodged in clothing, vehicles and animals. Seeds can also be spread in mud and contaminated agricultural produce (i.e. fodder and pasture seed) (Weeds of Australia Biosecurity Queensland Edition). However, per personal communication with Joseph DiTomaso, "This is not a primary means of dispersal. I think only animals and wind are the main methods." As such, this is scored a 'No'. There is no documentation of "frequent" dispersal via contaminated seed, equipment, etc.