Aspects of the Biology and Ethnobotany of Parasitic Angiosperm Species In Nigeria

Parasitic plants continue to gain research attention due to their remarkable lifestyle pattern that clearly cites them as a typical example of a biological oddity. They have defiled the basic characteristics of plants to become dependent on other plants for existence. Aside from their unique heterotrophic mode of feeding, host range and preference, seed germination clues, distribution patterns vary across different parasitic plants, which has partly ensured their presence in virtually every plant community. Among the above-listed factors, host range and preference, in particular, appears to be a major significant factor that shapes their distribution around the world, enabling certain species to thrive in various microclimates. The Nigerian environment has heterogeneous vegetation, traversing mangroves, rainforest, savannah vegetation, and its home to host parasitic plant species, including endemic, natives, and exotic ones. The present chapter gathered and synthesized available information regarding parasitic plants in Nigeria, particularly their biology and the host species supporting their population. Aside from the devastating menace some parasitic plants are known for, this report recognizes their ethnobotanical relevance. Thereby stimulating research interest in these highly specialized plant groups.


Introduction
Parasitic plants are an exceptional group of plants that have defiled plants' basic characteristics of solely synthesizing their own organic nutrient into dependent on other plants for survival [1]. Consequently, they have adapted to an association with a host plant using a physiological bridge known as the haustorium, where water and organic nutrients are transported [2]. This form of association enables the host plant to shape the distribution of the parasite. Based on the degree of host dependence, parasitic plants can exert their impact on an individual or community basis; some parasitic plants, for example, Striga, can severely reduce host performance, leading to host death, while others like Thonningia sanguinea exert a mild effect on its host. On a community scale, parasitic plants can significantly orchestrate changes in community structure, diversity, vegetation cycling, and zonation by either altering the competitive balance between host and nonhost plants [3] or necessitating an irregular uptake of host solutes which consequently *Order having a representative genera in Nigeria. Compiled from: The Angiosperm Phylogeny Website (APG III, & VI); [5], and Christenhusz, and Byng [6]  The phytogeography of Nigeria could broadly be categorized into two major regions; the Sudano-Zambezian and the Guineo-Congo [9]. The Northern part of the country falls under the Sudano-Zambezian region, comprising the Sudanian and Sahelian domains. The Guineo-Congo region of Nigeria is made up of Guineo domain to which the west and central part of the country belongs, and the Congo domain has the eastern part of the country. The different domains support various plant species, some of whom are notable host species to the parasitic plants domiciled in the Nigerian environment. For the current discourse on the distribution of parasitic plants, the Nigerian environment will be characterized into two, Northern Nigeria, predominately, savannah, and Southern Nigeria, where the rainforest forest belt is located.

Northern Nigeria
Northern Nigeria has a Savannah ecoregion, comprising the Guinea savanna bordering the rainforests, the Sudan savanna, and the Sahel bordering the desert. The guinea savanna is found in Kaduna, Kwara, Kogi, and Benue states; the Sudan savanna, in Kano and parts of Borno, Sokoto, Niger, and Bauchi states; and the Sahel around the Lake Chad. The savanna ecoregion is renowned for a climate that has a short wet and long dry season. The average monthly temperatures are around 29°C during the hot season and around 18°C during the cool season. The total annual rainfall varies greatly from around 500 mm in regions on the semidesert fringes to about 1500 mm in regions bordering the rain forests. The savanna rainfall is insufficient to support a rich growth of trees but is mostly dominated by perennial grasses with few tree clumps. In the Guinea savanna, the grasses grow tall during the rainy season. Trees occur quite close together, especially along the rain forest fringe. The grass is shorter in the drier Sudan savanna, and the trees are fewer and more scattered. In the Sahel, which is borders the Sahara desert, the land is quite bear with clumps of short grass and a few isolated shrubs and trees. During the dry season, the grass is usually dry and brown, and bush fires are common occurrences. The underground parts of the grasses survive the dry season and fires and grow again when the rains come. In terms of the parasitic plant distribution, the Nigerian Savanna is home to one of the most devastating parasitic genus, Striga. The species are found on cultivated lands, abandoned farmlands, and waste and weed-infested sites, depending on the presence of the host crop. Striga astiatica, S. aspara, S. hermonthica, S. gesnerioides are some of the species found in the savanna habitat. The basis for their occurrence only in the savanna part of the country is yet to be fully ascertained. Mohamed et al. [10] reported that the rain forest's high rainfall and moisture levels result in a "wet dormancy" of Striga seeds, consequently precluding its occurrence in the zone. Notwithstanding, most host crops, such as Corn, sorghum, and sugar cane, are cultivated majorly in the savanna part. Hydnora abyssinica, a root holoparasitic plant, was recently spotted around Nekong, Wusali ward, Kanke Local Government Area, Plateau State, Nigeria [11]. Notable members of the Loranthaceae family like Agelanthus dodoneifolius, A. heteromorphus, Globimetula cupulata, Tapinanthus cordifolius, T, globiferous, T. pentagonia, and T. preussii are attached to trees and shrubs in this zone. Table 2 shows potential distribution and host species of common parasitic plants of Nigeria

Southern Nigeria
The Southern part of Nigeria experiences heavy and abundant rainfall due to its proximity to the equatorial belt. It comprises majorly the rainforest and the swarm forest that borders the Southern Atlantic Ocean. The rainforest belt occurs in the regions that lie between the equator and latitude 5 o − 10 o N and S. The climate in  Table 2.
Potential distribution and host species of common parasitic plants of Nigeria. the tropical rainforest region is hot and wet throughout the year. The mean annual temperature is 27°C while the mean total annual rainfall is 2000 mm. The rainforest is characterized by dense and stratified vegetation, comprising various broad-leaved tree species sandwiched by lianas and herbaceous climbers. The rain forest covers Oyo, Edo, Delta, Imo, Cross River, Ogun, Ondo, and Rivers state, while the swarm forest is situated across the Niger Delta region. Parasitic plants are very much represented in the Nigerian rainforest. The largest parasitic tree, Okoubaka aubrevillei, is found here. It is believed to parasitize neighboring trees as an adaptive mechanism for creating light spaces in the normally thick rain forest environment. A recent report indicates that the parasitic tree is currently facing a decline in its Population due to forest degradation. Consequently, further isolating the few remnants stands in some forest areas of Edo, Cross River, and Osun States. Another interesting parasitic species found in the Nigerian rain forest is the ground-dwelling, herbaceous plant-Thonningia sanguinea, commonly refer to as 'ground pineapple' because they bear morphological similarities.  [11]. The first and only report of its existence was around Nekong, Wusali ward, a lowland area in the Sudan-savanna zone in Kanke Local Government Area, Plateau State, Nigeria [11]. Hydnora abyssinica is a perennial herb composed entirely of roots with extremely reduced vegetative morphology. It only emerges above ground when fruiting or flowering. H. abyssinica grows in a semiarid environment. The adaptation for such an environment might be related to the fact that water availability affects flower growth, including perianth splitting [29]. The flowers of H. abyssinica are protogynous; however, both cross and self-pollination can occur. Carrion flies and dermestid beetles carry out pollination. Generally, Hydnora species use a system similar to the pitcher traps of Carnivorous plants by trapping insects that fall into the flower tube, ensuring they do not escape [25].

LAURALES: cassytha filiformis (Lauraceae)
The genus Cassytha consists of about 17 species globally, with Cassytha filiformis being the predominant species in Nigeria. Cassytha filiformis is a perennial, leafless twining plant with a stem turning clockwise around the support plant [30]. It is less selective in terms of the choice of the host; hence any plant may be used as a host [29]. Stems are green to orange, filiform, and glabrous. Leaves are reduced to minute scales, ca. 1 mm long, easiest seen near tips of stems. Flowers are sessile and few in spicate inflorescences 1(−2) cm long, each subtended by an ovate bract and two ovate bracteoles. The inflorescence is a short raceme or spike. C. filiformis produces false fruits enclosed in the accrescent floral tube; dried floral parts persist in the fruiting stage. Information regarding the pollination biology in Cassytha filiformis is scanty. However, the floral characteristics point to wind pollination, while on the other, the presence of gland in the flowers point to insect pollination. Birds disperse fruits. Bush fire has been reported to promote the germination of Cassytha seeds [29].

SANTALALES: nigerian loranthaceae
Loranthaceae is the largest family in Santalales with about 73 genera and over 900 species [29]. It has a wide distribution particularly in the southern hemisphere, including both subtropical and tropical areas. Members of Loranthaceae have mostly stemmed parasites, with exception of a few root parasites. They possess both primary and secondary haustoria. Loranthaceae leaves are usually evergreen, leathery, and simple with smooth edges but variable forms, from broad flat leaves to cylindrical succulent leaves. Flowers are nearly always bisexual, with 4-7 perianth members who normally are of the same color. Stamens occur in the same number as the perianth parts, but there is only one pistil. Insects and birds, especially  (Figure 1). Generally, these representative species are distributed into two main groups distinguished by the flower bracts, the Tapinanthoid and the Taxilloid group.
The Tapinanthoid group has simple to branched hairs. There are three flower types in this group. Some possess relatively small, non-explosive flowers, which are mostly adapted to pollination by insects. They are considered primitive for example is Helixanthera mannii, H. spathulata. Others like Agelanthus and Englerina have explosive flowers, and their corolla is vented. Corolla venting occurs when there is a split in the corolla and the number of splits corresponding to the number of fused petals below the corolla tip. Agelanthus is the most species-rich Loranthaceae in Africa. It flowers all year-round depending on the host species and the location, usually much more abundant during the rainy period. Englerina is mostly shrubs up to 2 m in size. The flowers are clustered in pedunculate umbels and often standing erect from horizontal branches. The corolla tube is relatively short, adapted to pollination by short-beaked birds. The opening mechanism of the flower with the obvious vents serves as signals to the pollinators that the bud is mature. Tapinanthus and Globimetula. are non-vented but explosive. The flowers explode without opening first by splits. Tapinanthus is a common genus in Nigeria. They are characteristically known to have a swollen tip of the corolla in the bud stage. The tip often has a color  different from the rest of the corolla and becomes darker as the bud matures. Such a dark color also serves as a signal to the pollinators that the bud is mature. It flowers all year-round depending on the host species and the location, for usually much more abundant during the dry period. Globimetula species are known to have just a primary haustorium. The buds have a prominent swelling at the tip like Tapinanthus.
The Taxilloid group has stellate hairs and has a flower that is both explosive and vented. Example Phragmanthera, which is the largest genus in this group. It has a large single primary haustorium. Several species of this genus are considered pests in plantations.

SANTALALES: okoubaka aubrevillei (Santalaceae)
Okoubaka aubrevillei is a rare tree endemic to West Africa (Figure 1). It is the largest parasitic plant and also produces the largest seeds known for any hemiparasite. It is a monoecious, deciduous tree that grows up to 40 m high [31]. The tree is thought to be useful for various folk medicinal purposes by different ethnic groups in all of its native ranges [21]. Okoubaka aubrevillei is perhaps one of the most controversial plants in Africa in terms of taxonomy and ethnobotanical information. It is believed that no tree grows within 80 feet of a 60 feet Okoubaka tree, except for Myrianthus arborea, Musanga cecropoides, Cola attiensis [31]. Its presence has been confirmed in three state locations in Nigeria: Edo, Cross River, and Osun States [32]. As exercised by Okoubaka aubrevillei, parasitism might be for nutritional purposes and as a means of competition for light since it dwells only in a rainforest habitat.
The leaf blade is ovate to oblong, simple and entire in shape, arranged in an alternate to almost opposite. Flowers are green in color and arranged on spines around older branches. Flowers are green in color. Unisexual flowers are present, with the female flowers slightly larger than male flowers [33]. The flowers develop into hard, yellow-colored ellipsoid drupes containing a single large seed that weighs up to 100 g. The tree is monoecious. Hence, it is expected that the plant undergoes self-fertilization (allautogamy), leading to genetic stability. Although little is known about the pollination biology, the pollination type is likely either by ants (myrmecophily) or bats (cheiropterophily) due to the small greenish flowers that preclude its chances of being pollinated by birds [32]. Seeds are speculated to be dispersed by large forest animals such as elephants.

SANTALALES: viscum spp. (Santalaceae)
Viscum congolense De Wild. And Viscum decurrens (Engl.) Bak. & Sprague are two representative species of the family in Nigeria. Reports on these species, particularly, Viscum decurrens are scanty. V. congolense is a dioecious, globose shrub that grows up to 50 cm tall and is found in humid forests, secondary forests, and plantation forests. Leaves are variable, elliptic-oblong in shape. The fruits are small, smooth and greenish-white in color [12].

Santalales: thonningia sanguinea (Balanophoraceae)
Thonningia sanguinea Vahl (Balanophoraceae) is a monotypic, rare, cryptic obligate holoparasitic plant endemic to tropical Africa (Figure 1). Its distribution is restricted to the forest environment, where it parasitizes forest trees [27,28]. Thonningia sanguinea is a fleshy dioecious herb growing from an underground tuber. It is parasitic on other plants via its tuber. The branching yellow tuber extends horizontally up to 10 or 15 centimeters through the soil. It forms bulb-like swellings at the points where it attaches to the roots of its host plants which could either be exotic or native species. These swellings, or galls, can reach over 18 centimeters wide [34]. The stem is coated with spirals of scale-like leaves. The leaves lack chlorophyll, as the plant obtains nutrients from hosts and does not need to photosynthesize. The flowering stem emerges from the ground to produce a bright red or pink inflorescence containing male and female flowers. The crowded flower heads are covered in scales. The inflorescence is up to 15 to 20 centimeters long [34]. Studies on its reproductive phenology suggest that T. sanguinea flowers all year round. The ant Technomyrmex species are the most common floral visitors, and it is hypothesized to be the pollinating agent [27,28].

LAMIALES: alectra spp. (Orobanchaceae)
Alectra is also known as the yellow witchweed. Representative species in Nigeria include Alectra sessiliflora var. monticola, Alectra sessiliflora var. senegalensis, and Alectra vogelii Benth. Generally, Alectra grows erect, emerging from a small bulb (haustorium) attached to the root of the root plant. The leaves are lanceolate, simple, subsessile, and arranged in an opposite or alternate pattern. Flowers are borne by a short peduncle and yellow in color. The fruit is a globular dehiscent capsule containing many seeds. At maturity, it opens in 2 valves. The seeds are tiny and ovoid. Seeds are dispersed mainly by wind. Alectra species, particularly Alectra sessiliflora var. senegalensis, are a serious threat to agriculture since they can use members of Papilionoideae such as cowpeas, peanuts, soybeans and other legumes as host.

Lamiales: striga spp. (Orobanchaceae)
Striga, often refer to as 'witchweed' because several species, despite their beauty, seem to perform "evil magic" like a witch. The life-cycle of Striga spp. is quite complex [48]. It begins a long period of seed dormancy that could persist for up to after which the seeds then need sufficiently warm and humid conditions for one to two weeks to enter into a condition in which they can germinate (pre-conditioning). Subsequently, they need host-derived signals that stimulate germination [25]. After germination, a special organ, called the haustorium, through which nutrient materials are siphoned from the host [25]. The above-ground part of the parasite emerges after haustorium development and proper attachment to the host. This is accompanied by flower bloom, pollination, and subsequently shedding the seeds as the capsules ripen. Pollination is by insects, probably butterflies; the seeds are tiny, produced in vast numbers and dispersed mainly by wind, but also stick with mud to hoofed and clover-trotted mammals [17].

SOLANALES: cuscuta australis R.Br. (Convulvulaceae)
Cuscuta, commonly referred to as dodder, is the only parasitic genus in Convolvulaceae, belonging to the order, Solanales. The species is represented in Nigeria by Cuscuta australis. Cuscuta spp. bear a close similarity to Cassytha in appearance. However, some notable differences include that most Cuscuta spp. are annuals, unlike Cassytha, a perennial herb. Also, while Cassytha is a hemiparasite, Cuscuta is holoparasitic. Also, Cuscuta is a more advanced parasite than Cassytha due to the presence of a direct phloem contact [16].
Aspects of the Biology and Ethnobotany of Parasitic Angiosperm Species In Nigeria DOI: http://dx.doi.org /10.5772/intechopen.98667 Cuscuta australis possess tiny, stalk or sessile flowers that are clustered in dense heads. Flowers are pollinated by insects; however, birds are responsible for seed dispersal [29].

Ethnobotanical relevance of parasitic plants
The term Ethnobotany was first used by Harshberger [35] to denote the study of plants used by primitive aboriginal people subsequently; different workers have defined the subject, greatly enlarged the scope and accepted it as an interdisciplinary science for a holistic approach to man-plant relationship, hence different definitions of the concept of ethnobotany exist. Allem, [36] defined the concept as the biological, economic and cultural inter-relationship between people and plants in the environment where they exist. Schultes and Raffauf [37] broadly defined the subject as human evaluation and manipulation of plant materials, substances and phenomena in societies. Jain [38] related it to the study of how people make use of plants. According to Pushpangadan and Kumar [39], it is the entire realm of useful relationship between plant and humans. These definitions point out a relationship between people of a given community or society, the environment and the plant diversity in that particular community.
Ethnobotany has now been recognized as an integral part of indigenous/local knowledge of a particular society. Thus, different societies or communities have their own knowledge about plants and their uses. Indigenous knowledge represents an immense valuable database that provides humanity with an insight into how numerous communities have interacted with the changing environment, providing local solutions for local problems and suitable ways for coping with challenges posed by specific conditions. According to Warren and Cashman [40], ethnobotanical knowledge is how most communities survived for centuries by adapting themselves to their environment, using their intrinsic knowledge of associated resource management.
Parasitic plants are keystone species in plant communities, exhibiting a unique and important ecological role [3]. They are common in many natural and seminatural ecosystems, from tropical rain forests to the savanna. Although some parasitic plant species are important pests of human agriculture and forestry, many are highly valued for food and wood as well as for their medicinal and esthetic properties [8].
The study and management of parasites have historically focused on the control, and even elimination, of parasite populations, for example, researchers have intensified efforts to eradicate several mistletoe species, Cuscuta: Striga, and broomrapes which attack food crops [35]. Despite this ecological and economic importance, parasitic plants have often been overlooked and excluded from most ethnobotanical checklist and flora assessment surveys [8]. Literature survey reveals that only in few instances have parasitic plants been recognized for their ethnobotanical value [41,42].
The importance of indigenous knowledge is overwhelming especially with regard to parasitic plants. Aiyeloja and Bello [43] valued it as the sum of the experience that forms the basis for decision making for familiar and unfamiliar problems and challenges in a local community. The overall ethnobotanical uses of parasitic plants are quite high. However, the traditional knowledge of these plants have been widely threatened by current trends of economic globalization that promote intensive agriculture, industrialization, and the migration of rural populations to urban areas. Consequently, it is crucial to record this fast-disappearing knowledge before it is lost along with the present generation of elderly persons. Table 3 shows the ehnobotanical relevance of parasitic plants. Alectra sessiliflora var. monticola (Engl.) Melch In Western Kenya, the flowers and leaves of Alectra sessiliflora are used to remedy toothache, diarrhea, kwashiorkor, and oral thrush in children, gastrointestinal and sexually transmitted infections. It is also used to hasten childbirth and to treat scars caused by leprosy. [44,45] Cassytha filiformis L. Several tribes use the whole plant of Cassytha filiformis in Nigeria in the treatment of cancers and gonorrhea. Also, to ease labour pains, quicken labour time, and lubricate the birth canal during childbirth. [46] Cuscuta campestris Yunck.
In Saudi Arabia, the whole plant of Cuscuta campestris is used as a purgative and also during constipation. [47] Englerina gabonensis (Engl.) Balle In Libreville (Gabon), the leaves of Englerina gabonensis are used to cure rheumatism. It is also used to heal fractures and scabies, treat mental illness, epilepsy and in performing magic (protection against robbery) [17] Globimetula cupulata (DC.) Van Tiegh In the Southeast part of Nigeria, the Leaves and fruits of Globimetula cupulata are used in the management of high blood pressure and diabetes mellitus [48,49] Helixanthera mannii (Oliv.) Danser In West Africa, Helixanthera mannii is used for religious ceremonies, superstitions, magic purposes too. [46] Hydnora abyssica A. Br. In Southern Mozambique, the inflorescence of Hydnora abyssica is used to treat diarrhorea, piles, acne, menstrual problems, stomach cramps, and to stop bleeding [50] Okoubaka aubrevillei Pellegr. & Normand.
In Southern Nigeria, the bark and the seeds of Okoubaka aubrevillei are used to treat convulsion, for rituals and prevention of miscarriage and as an anaphrodisiac. The bark and leaves are used for reducing swollen testicles (orchitis). The branch is tied on a broken limb along with other plants for the healing of the limbs. Use of the bark infusion or maceration in water to treat skin problems (including those caused by syphilis and leprosy). In contrast, external applications of bark preparations are used to counteract poisoning. [32,46,51] Phragmanthera capitata (Spreng.) Balle In Logbessou, in the North of Douala (Cameroon), the leaves and branches of Phragmanthera capitata are used for treatments of Nerves attacks, convulsions, chronic muscular pains, diabetes, respiratory dysfunctions, rheumatism related pains, epilepsy, dizziness, uterine hemorrhage, hypertension, hypotension, back pains, kidney pains, menopause, headache, heart palpitations, general purifications, irregular menstruations and nose bleeding. [22,24] Phragmanthera kamerunensis (Engl.) Balle In southwest Nigeria, the leaves of Phragmanthera kamerunensis is used for the treatment of gastric ulcer. [23] Striga asiatica L. In South Africa, the stem and leaves of Striga asiatica are used for treating hemorrhoids, or smoldering smoke is used to kill off warts, or charred remains are used as a dressing on wounds to dry or rubbed on legs for oedema. [52] Striga hermonthica (Del.) Benth In Northern Nigeria, the stem and leaves are used to treat dermatosis, leprosy ulcer, pneumonia and jaundice [53] Tapinanthus bangwensis (Engk. & K. Krause) Danser.
Southwest Nigeria leaves; the whole plant is used to treat circulatory and respiratory disease problems, malaria, diabetes, hypertension and sterility in cows. [54,55]

Conclusion
Parasitic plants play a vital role in plant communities, and their diversity is quite huge, with various species inhabiting the different ecosystems in Nigeria. The study and management of parasites have historically focused on controlling and even eliminating parasite populations. Although some parasitic plant species are important pests of human agriculture and forestry, many are highly valued for food and wood and their medicinal properties. The current chapter provides an update on the various potential uses of parasitic plants in Nigeria from an ethnobotanical perspective. Therefore it is important to look beyond just their economic implications and approach the conservation of parasitic plants holistically. Next time you walk along nature trails in the forest, look out for some stem parasites on the branches of trees and root parasites at the base of host plants.

Species Geographical location; plant parts use; ethno-uses References
Thonningia sanguinea (Vahl.) In Southern Nigeria, the whole plant is used with other materials against anemia, asthma, diarrhea, infant illness, rheumatism, skin infection, sore throat, stomach upset. It is also valuable as (a) an aphrodisiac [8]  © 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.