R. fistulosa is a broad-leaved, annual, facultative hemi-parasitic forb species found in wetlands in tropical Africa (e.g. Hansen, 1975;Ouédraogo et al., 1999). When these wetlands are used for crop production, the species may develop into a (parasitic) weed (Bouriquet, 1933;Rodenburg et al., 2011b).
Plant Guide REDTOP Agrostis gigantea Roth Plant Symbol = AGGI2 Contributed by: USDA NRCS Idaho Plant Materials Program Figure 1. Redtop (Agrostis gigantea). Photo by Robert Soreng @ USDA-NRCS PLANTS database. Alternate Names Agrostis alba auct. Non. L. Agrostis depressa Vassey Agrostis palustris Huds. Agrostis stolonifera L. var. major (Gaudin) Farw. Black bent Carpet bentgrass Redtop bent Redtop bentgrass Redtop has undergone numerous name changes over time, and the actual placement of the multiple species and varieties remains confused due to hybridization...
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R. fistulosa is a relatively unknown species at present and therefore it is often unnoticed by local extension and research (as observed in Benin, Cote d’Ivoire, Madagascar, Senegal, Tanzania and Uganda). The species is also easily overlooked as the flowers are only opening at sunset (Cissé et al., 1996).
R. fistulosa can be confused with several species, including Cycnium recurvum (Oliv.) Engl. (previously named R. fistulosa recurva Oliv. and R. tenuisecta Standl.), which has a similar plant type and overlapping distribution in parts of North-East and South-East Africa. However, the tube of the corolla of C. recurvum is about one third of that of R. fistulosa. Moreover, C. recurvum has a distinctly different habitat, favouring dry conditions (Mielcarek, 1996).
The closely-related genera Rhamphicarpa and Cycnium are distinguished by the form of the capsules and the presence of a beak on their capsules: Rhamphicarpa have oblique ovoid capsules with beaks, whereas Cycnium have straight oblong capsules without a beak (Cycnium) (Staner, 1938).
Another distinctive feature is the stamens: Rhamphicarpa stamens are didynamous, arising at 2 levels in the corolla tube, and the style exceeds the stamens, whereas in Cycnium the style never exceeds the lower pair of stamens, and stamens are equal in length, arising at 1 level in the corolla tube (Philcox, 1990;Fischer, 1999;Leistner, 2005).
Due to their parasitic nature, and similarities in host crop ranges, local names given by farmers are often the same for both R. fistulosa and Striga spp. (J Rodenburg, personal observation). R. fistulosa is sometimes even referred to as ‘the Striga of rice’, even though both R. fistulosa and Striga spp. parasitize rice. Striga spp. are usually found on rice grown in the free-draining uplands, whereas R. fistulosa parasitizes rice in the water-logged lowlands and hydromorphic zones.
R. fistulosa is a broad-leaved, annual, facultative hemi-parasitic forb species very widespread in the wetlands of tropical Africa (Staner, 1938). It has also been reported in India, New Guinea and Australia. No hard evidence is published on the invasiveness of R. fistulosa. Although R. fistulosa is not yet considered to be a widespread problem, it has the potential to become more important in the near future (Raynal Roques, 1994;Rodenburg et al., 2010;2011a), especially since it can develop into a parasitic weed when it encounters a suitable host plant (e.g. Akoegninou et al., 1999). It parasitizes cereal crops like rice and there are indications that it is increasingly common on rain-fed lowland rice (Rodenburg et al., 2011b). Given its very widespread distribution (more than 35 countries in sub-Saharan Africa), the species is likely to be, or become, a very serious parasitic weed, threatening rice production in the continent.
R. fistulosa parasitizes wild grass species (of the Poaceae family) and is a facultative hemi-parasitic weed on cereal crops like rice, maize and millet (Bouriquet, 1933;Kuijt, 1969;Cissé et al., 1996;Ouédraogo et al., 1999). Groundnut Arachis hypogaea L. (Bouriquet, 1933) and cowpea Vigna unguiculata (L.) Walp. (Kuijt, 1969) have been reported as hosts too, although the latter report concerned R. veronicaefolio Vatke (= Cycnium veronicifolium Vatke), rather than R. fistulosa (Fuggles-Couchman, 1935).
Rice, particularly direct seeded rice (Johnson et al., 1998), is the most affected crop, as this is the only major cereal crop that can be grown in the temporary flooded conditions of the rain-fed lowlands where R. fistulosa thrives (Rodenburg et al., 2010;2011b).
Supposedly R. fistulosa can also parasitize members of the monocot Cyperaceae as well as the eudicot Leguminosae and Labiatae families (Bouriquet, 1933). It is very unusual for a parasitic plant species to be able to parasitize both monocotyledons and eudicotyledons, and so these reports need to be confirmed.
R. fistulosa is a facultative hemi-parasite and as such it is not dependent on the presence of a host to complete its life cycle. However, the parasite obtains a reproduction advantage from parasitizing a suitable host plant (Ouédraogo et al., 1999;Rodenburg et al., 2011b).