Sedges are grass-like plants widely distributed especially in the tropics and subtropics belonging to the genus Cyperus in the family Cyperaceae. The differences easiest to see between sedges and grasses are:
1) that grass stems are usually but not always round in cross section, while sedge stems are more or less triangular;
2) sedge leaves are spirally arranged in three ranks while grasses have alternate leaves forming two ranks; and
3) leaf sheaths (lower part of a leaf enclosing the stem) in grasses are split whereas leaf sheaths of sedges are not split.
Sedges are mostly found in moist areas such as wetlands, but are also common constituents of forest-margin vegetation. Like most tropical plants, they are sensitive to frost. Renewed attention is being paid to these plants due to their critical role in wetland ecosystems.
Genus Cyperus comprises about 650 species of which 207 are found in East Africa. Some of the commonly occurring species in the region include:
C. blysmoides (C. bulbosus var. spicatus) (Water Grass): It is a perennial sedge. It is limited to the highlands (500-1800 m) of East Africa (Kenya, Tanzania and Uganda) and it is also present in Ethiopia. It is abundant as a weed in some upland crops such as coffee and wheat. It is propagated by bulbs (they are flattened stems bearing fleshy leaves and serve as organs of storage and vegetative reproduction).
(Highland Nut Sedge):
It is a perennial sedge that is widespread in the highlands (1200-3350 m) of East Africa. It can be a problem in pastures, and for pyrethrum and other crops, especially where there is little or no cultivation. It is propagated by rhizome
s (a root-like underground stem) and tubers.
C. teneristolon (C. transitorius; Kyllinga pulchella):
A perennial sedge localized in the uplands of Kenya and Tanzania. It is also present in Ethiopia. It is a weed of crops in the highlands. It is propagated byrhizome
s and seed.
(Papyrus, Papyrus Sedge or Paper Reed):
It is a stately aquatic member of the sedge family. It is a herbaceous perennial native to Africa. This tall, robust, aquatic plant can grow 4 to 5 m (13 to 16 ft) high. It forms a grass-like clump of triangular green stems that rise up from thick, woody rhizome
s. Each stem is topped by a dense cluster of thin, bright green, thread-like stems around 10 to 30 cm (4 to 10 in) in length, resembling a feather duster when the plant is young. Greenish-brown flower clusters eventually appear at the ends of the rays, giving way to brown, nut-like fruits. Papyrus sedge (and its close relatives) has a very long history of use by humans, notably by the Ancient Egyptians'. It is the source of papyrus paper, parts of it can be eaten, and the highly buoyant stems can be made into boats. It is now often cultivated as an ornamental plant.
Distribution and ecology
C. papyrus grows in full sun, in wet swamps and on lake margins throughout Africa, Madagascar and the Mediterranean. In deeper waters it is the chief constituent of the floating, tangled masses of vegetation known as sudd. Papyrus ranges from subtropical to tropical desert to wet forests, tolerating annual temperatures of 20 °C to 30 °C and a pH of 6.0 to 8.5. Papyrus flowering prefers full sun to partly-shady conditions. Like most tropical plants, it is sensitive to frost. The "feather-duster" flowering heads make ideal nesting sites for many social species of birds. As in most sedges, pollination is by wind, not insects.
Mature nut-like fruits are distributed by water
C. esculentus (Yellow Nut Sedge, Earth Almond, Tiger Nut Sedge or Chufa Sedge):
C. esculentus is a light green perennial sedge growing to about 1 m in height with solitary stems growing from a tuber. The stems are triangular in section, and bear slender leaves 3-10 mm wide. The flowers of the plant are distinctive, with a cluster of flat oval seeds surrounded by four hanging leaf-like bracts (modified leaves from where flowers arise) positioned 90 degrees from each other. The plant foliage is very tough and fibrous, and is often mistaken for a grass.
Distribution and ecology
It is present in over 20 African countries. It is widespread above 500 m in Kenya, Tanzania and Uganda but most common in the highlands (1500-2100 m). It is widely distributed in arable land and irrigated areas.
Host range and damage
It can be a serious weed of coffee, cotton, groundnut, maize, pineapple, rice, sisal, soybean, sugarcane and vegetables. If left unchecked, C. esculentus can cause a yield loss of over 40% in maize and soybean.
It produces tubers which are nearly spherical, about 10 mm in diameter
, dark brown in colour. Tubers are edible with a slightly sweet, nutty flavour. It is commercially grown for these tubers in some countries (e.g. Burkina Faso, Ghana, Mali, Nigeria and Spain). The tubers are quite hard and are generally soaked in water before they can be eaten, thus making them softer and giving them a better texture. They are eaten as vegetables, made into sweets or used to produce the famous "Horchata de chufas" (a creamy white drink) of the Valencia region in Spain. They have excellent nutritional qualities with a fat composition similar to olives and a rich mineral content, especially phosphorus and potassium. The oil of the tuber was found to contain 18% saturated (palmitic acid and stearic acid) and 82% unsaturated (oleic acid and linoleic acid) fatty acids. "Horchata de chufas" can be useful in replacing milk in the diet of people intolerant to lactose to a certain extent. Since the tubers contain 20-36% oil,C. esculentus has been suggested as potential oil crop for the production of biodiesel.
Dispersal: Seed and tubers are an important means of dispersal of this species.
(Coco-grass, Purple Nut Sedge or Red Nut Sedge):C. rotundus
is a perennial plant that may reach a height of up to 40 cm. The names "nut grass" and "nut sedge" (shared with the related species Cyperus esculentus
) are derived from its tubers, that somewhat resemble nuts, although botanically they have nothing to do with nuts.
As in other Cyperaceae
, the leaves sprout in ranks of three from the base of the plant. The flower stems have a triangular cross-section. The flower is bisexual, reddish-brown to purplish-brown. The fruit is a three-angled achene (small, dry, not opening when ripe, one-seeded).
The root system of a young plant initially forms white, fleshy rhizome
s. Some rhizome
s grow upward in the soil, and then form a bulb-like structure from which new shoots and roots grow, and from the new roots, new rhizome
s grow. Other rhizome
s grow horizontally or downward, and form dark reddish-brown tubers or chains of tubers.
It is a species of sedge native to Africa, southern and central Europe (north to France and Austria), and southern Asia. C. rotundus is one of the most invasive weeds known, having spread out to a worldwide distribution in tropical and temperate regions. It has been called "the world's worst weed" as it is known as a weed in over 90 countries, and infests over 50 crops worldwide
Primary hosts: Gossypium spp. (cotton), Saccharum officinarum (sugarcane), Citrus spp., Coffea spp. (coffee), Arachis hypogaea (groundnut), Zea mays (maize), Oryza sativa (rice).
Secondary hosts: Syzygium aromaticum (clove), Cocos nucifera (coconut), Allium cepa (onion), Capsicum annuum (bell pepper), Fragaria sp. (strawberry), Agave sisalana (sisal hemp), Sorghum, Glycine max (soybean), Camellia sinensis (tea),Lycopersicon esculentum (tomato), Triticum (wheats).
Damage C. rotundus
is considered the worst weed based on its occurrence in 52 crops in 92 countries and its capacity to cause substantial yield losses. Examples of crop loss caused by C. rotundus
include 35-89% in vegetables, 30% in cotton and 75% in sugarcane harvest. Even the growth of tree crops can be reduced, for example, mulberries in Japan, citrus in Israel and coffee in Kenya. Much of this can be attributed to the capacity of C. rotundus
to remove nutrients from the soil and store them in its tubers, making them unavailable to crops. Adding nitrogen to a crop can actually improve the competitiveness of C. rotundus
, causing even greater crop loss than where no fertilizer is added. C. rotundus
undoubtedly competes with crops for water but also for light when it grows tall enough. There is evidence that extracts from C. rotundus
suppress the growth of plants but it is difficult, under field conditions, to separate the effects of allelopathy
(the roots releasing substances harmful to other plants) from competition.
It is claimed that C. rotundus
is an important medicine in India and China and noted for its use by pharmaceutical companies to produce diuretics
, anthelminthics and treatments for coughs, bronchial asthma and fever. It makes a poor fodder but has value in binding together soil. However, its negative attributes as a weed far outweigh its usefulness.