Xu Zhigang

Higher plants that rely on host plants to provide water, inorganic salts or all nutrients for growth and reproduction. They can all blossom and bear seeds, so they are also called parasitic seed plants. The roots, roots and leaves of this kind of plants are degraded, so they can't feed themselves independently and must live on other plants. Host species vary greatly due to different parasitic plants, most of which are wild plants and a few are parasitic on crops or fruit trees. Different kinds of parasitic plants will harm herbs, ornamental plants and medicinal plants, fruit trees and street trees in the field.

Distribution and harm

Parasitic seed plants are widely distributed in tropical areas, such as rootless vines, one-legged grasses and parasitic vines. Some are in temperate zones, such as dodder, mistletoe and so on. A few are in dry and cold high latitude or high altitude areas, such as Liedang. The harm of parasitic seed plants to the host varies greatly due to the difference of parasitism and parasite density. The main influence of parasitic loranthus is to compete with the host for water and inorganic salts, rather than organic nutrients, which has little effect on the host. If the parasite population is large, the harm is obvious, which often causes the host plant to wilt or decrease its vitality and yield. The predation and harm of Cuscuta chinensis to the host is very obvious, especially when the population density is high, the host is seriously damaged and can be completely destroyed, resulting in crop failure.

Although some higher plants, such as orchids, have their own roots and leaves and enough chlorophyll for food, they often attach to some woody plants and absorb inorganic salts or soluble substances from their surfaces, which has no obvious harm and influence on the host and has not established parasitic relationship. This plant is called epiphyte.

parasitic

Parasitic plants obtain living matter from host plants in different ways and components. According to the different ways of obtaining host nutrition, parasites can be divided into total parasitism and semi-parasitism. The parasitic way of obtaining all the living materials needed by the host plants is called "total parasitism", such as orphan grass and dodder. Their leaves degenerate, chlorophyll disappears, and their roots become root-sucking. The catheter and sieve tube in the root suction of parasitic plants are connected with the catheter and sieve tube of host plants respectively. They have stout or developed stems and flowers, which can produce a large number of seeds, causing serious damage to host plants and often causing them to die prematurely. There are chlorophyll in the stems and leaves of mistletoe and mistletoe, which can make their own nutrients, but the roots are degraded. The root suction catheter is connected with the host vascular bundle catheter to absorb the water and inorganic salts of the host plant. The parasitic relationship between parasites and hosts is mainly dependent on water. This kind of parasitism is called "semi-parasitism", also known as "water parasitism" Some parasitic plants, such as one's feet, have turned their leaves into scales. Although they contain a small amount of chlorophyll, they are not self-sufficient and still need nutritional supplements from their hosts. According to different parasitic parts, it can be divided into two kinds: root parasitism and stem (leaf) parasitism. The roots of host plants are parasitized by Centella asiatica and Polygonum multiflorum, and are separated from the host plants on the ground, which belongs to "root parasitism". Rootless vine, dodder and mistletoe are closely combined on the stems, branches and leaves of the host. This parasitism is called "stem (leaf) parasitism".

Plants of the genus Paraparasite of Santalaceae are often parasitic on plants of the parasitic family, such as mistletoe, Taxilli, COLEOPTERA and COLEOPTERA. The host of Taxillidae is broad-leaved tree species. This parasitism with Moraceae as the host is called "heavy parasitism".

range

Although different kinds of parasitic plants spread through seeds, the transmission dynamics and modes are quite different. The mode of transmission mostly depends on wind or bird media, and some of them spread with host seeds, which is a passive mode of transmission. After the seeds of a few parasitic plants mature, the fruits absorb water, swell, crack and pop out the seeds, which belongs to the type of active transmission. The fruits of Taxillidae are fleshy berries, which are brightly colored when ripe, attracting birds to peck and spreading with the flight activities of birds. These seeds will not be damaged when passing through the digestive tract of birds. When it is excreted with feces, it will adhere to branches, and when the temperature and humidity conditions are suitable, it will germinate and invade the host. Seeds of Polygonum multiflorum Thunb. And Polygonum multiflorum Thunb. Very small. When mature, the capsule cracks and the seeds scatter and spread with the wind, generally reaching about 10 meter. Seeds or capsules, such as dodder, often spread and spread with the harvest and transportation of host (soybean) seeds. When the fruits of Taxodium ascendens and Viscum mistletoe are ripe, they tend to absorb water and swell until they burst and the seeds are ejected. The ejection distance is generally 3 ~ 5 meters, and the farthest can reach 15 meters. The ejected seeds have mucus on the surface, which is easy to attach to the surfaces of other host plants and can germinate and invade under suitable conditions.

Major groups

There are many kinds of parasitic higher plants, about 2500 species, which belong to angiosperms in taxonomy, mainly including convolvulaceae, Lauraceae, Taxillidae, Orphantiaceae, Scrophulariaceae, Santalaceae and other plants.

loranthaceae

Including 65 genera of Taxilli and Viscum, there are about 300 species of plants/kloc-0. Most species have chlorophyll in their bodies, which is a semi-parasitic lifestyle. A few species have no chlorophyll and are completely parasitic. The hosts are woody plants, including gymnosperms such as conifers and angiosperms such as mulberry, camphor tree, chestnut and poplar. Most of them are distributed in subtropical and tropical regions, and some of them appear in temperate regions. Most mistletoe plants are shrubs and few are herbs. Leaves opposite occasionally alternate, entire, or reduced to scales, without stipules; Flowers are bisexual or even unisexual, mostly racemes. Most of them are stem parasites and a few are root parasites. Important parasites are Tolypanthus, Macrosolen, Elytranthe, Helixanthera, Dendrophthoe, Scurrula, Taxilli and Tolulus. Chestnut (Korthalsella), Taxodium and mistletoe.

Ikebana

Commonly known as "dwarf mistletoe", it is more common in America and Asia, and its hosts are pine, cypress and fir. The damaged trees are short and the wood is loose. The seedlings were injured and died early. Mistletoe often grows in bundles or scatters on branches, forming crazy branches. The stem height of this parasite is less than 10 cm, and a few species are only 1 ~ 2 cm, without branching. The stem is yellow or brown, with small leaves and scales, opposite to the stem and the same color. The branching haustorium is produced at the base of the stem and grows parallel to the stem outside the cambium of the host, thus radially branching into the xylem and phloem of the host to absorb the nutrients and water of the host, which is close to the mode of total parasitism. Parasitic branches can grow continuously from around the infected site. 4 ~ 6 years old parasitic branches can blossom and mature in 5 ~ 16 months after pollination. Dioecious, the male branches die after flowering, and the female branches die after the seeds mature. This kind of fruit is a berry. When the seeds are ripe, the berries absorb water and produce great pressure, which ejects the seeds with a range of 15 meters. There is a lot of mucus on the outside of seeds, which is easy to attach to adjacent branches. Berries can also be pecked around by birds and passed on.

mistletoe

It is distributed all over the world, especially in temperate regions, which mainly harms trees, deciduous shrubs and orchard trees and causes economic losses in some areas. However, it is lighter than pine and Chinese fir. There are clumps of parasitic branches on the branches of damaged trees, which are more obvious after defoliation in winter. Sick trees can usually live for many years without dying soon. Most of them parasitize on branches with the host diameter of 1 ~ 2 cm, and a few can parasitize on branches of about 30 cm. The height of parasitic branches varies from 1 ~ 2 cm to 1 m, with obvious nodes and internodes; The leaves are opposite and contain chlorophyll. Berry contains 1 seed, which is mainly carried by birds after pecking. Most berries ripen in winter, first milky white, then red. In Europe, it is often used as a home decoration for Christmas and regarded as a mascot.

Parasitic mulberry

Mainly distributed in temperate zone and subtropical zone, the hosts are mostly broad-leaved trees or shrubs, and the growth of the injured hosts is slightly affected. The height of parasitic branches varies from 10 to 50 cm, but there are no obvious nodes; Pinnate vein; Bisexual flowers, bracts 1, bracteoles 2, bract ribs, spikes, anthers spherical; The fruit is a berry, which is pecked and spread by birds when it is ripe. Whole grass can be used as medicine.

Ledanko

Including 15 genus, about 180 species, mainly distributed in the north temperate zone, with a few in Africa and Oceania. There are 9 genera and 40 species in China, which are mainly distributed in northwest, north and northeast, and a few are distributed in high altitude areas in southwest. As completely parasitic root parasitic herbs, most of them are specialized and have fixed hosts, and a few are extensive. Stem height 10 ~ 50 cm. The meat is stout, most of them are unbranched, and a few of them can be branched and can be used as medicine. Leaves are small, degenerate into scales, and contain no or almost no chlorophyll. The top of the stem is densely covered with flowers, forming spikes or heads. The flowers are bisexual, the pistil ripens first, the calyx is tubular, cup-shaped, bell-shaped or spoon-shaped, the corolla is often curved, lip-shaped, with 4 stamens and 2 strong stamens, which are inserted in the middle of the corolla. The ovary is superior, the placenta is on the lateral membrane, the fruit is a capsule, the ventral surface is cracked, the exocarp is slightly hard, the seeds are small, and the seed coat is concave or reticulate. Most of the hosts are herbs, mainly Leguminosae, Compositae and Cucurbitaceae, which are extremely harmful to crops and can make crops extinct in severe cases. The important genera are Boschniakia, Cistanche deserticola, Phacellanthus, Aeginetia, Christisonia, Lathraca and Orphania.

Boshnyak ya

All parasitic herbs, with spherical or cylindrical rhizomes, often with 1 ~ 3 erect stems, unbranched and stout meat. Leaves triangular, scaly, spirally arranged on the stem, racemes, densely flowered, sessile, calyx cup-shaped, corolla, tube expanded into sacs, stamens exposed. The flowering period is from May to July, and the fruiting period is from July to September. It is distributed on hillsides, forests or rivers at an altitude of 1500 ~ 1800 meters in the northeast of Japan, Korea and China. The host plant is mainly Alnus cremastogyne.

broomrape

Belongs to the entry plant quarantine object (see Liedang).

Aralia

Millet, stem height 15 ~ 35 cm, branched from the base, yellow-brown; Leaves are scaly and sparse; Flowers purple, solitary, long pedicel, spatulate calyx, obliquely split on one side, about 2 cm long, corolla lip-shaped, 2 ~ 3 cm long, slightly curved tube, shallowly split at the top. The capsule is conical with small seeds (see figure). The whole herb can be used as medicine, which has the effect of detumescence and detoxification. It is distributed in the provinces south of the Yangtze River basin, and also occurs in Japan, North Korea and India. The host plants are mainly Gramineae.

Convolvulaceae

Only Cuscuta chinensis belongs to parasitic life, including 170 species, and there are 14 species reported in China. It occurs all over the world, with a wide range of hosts, mainly Leguminosae, Compositae, Polygonaceae, Rosaceae, Solanaceae, Umbelliferae and Liliaceae, and occasionally Gramineae plants are killed. Cuscuta chinensis is a completely parasitic herb. Its leaves degenerate into scales, and its stems are yellow filaments, which are wrapped around the stems and leaves of the host plants and connected with the vascular bundles of the stems of the host plants through haustorium, absorbing water and nutrients, often resulting in serious losses (see Cuscuta chinensis).

lauraceae

There are only about 20 species of Kasesa with parasitic ability.

Rootless vine is a sticky and parasitic herb, also known as headless grass and nettle vine. Dish-shaped roots are adsorbed on the host plants, and the stems are linear, branched, green or greenish brown, while dodder has yellow-brown filamentous stems, which is the main difference between them. Leaves degenerate into small scales; Flowers are small, bisexual, born between scaly bracts, spikes or heads. Corolla is gyro-shaped, with 6 lobes arranged in two rounds, 9 stamens fertile and 3 degenerated. Capsule with membranous or leathery seeds, flowering from May to 65438+February. Most of them are distributed in tropical and subtropical regions, especially in northern Australia. There is a species (Cassytha filiformis) in southern China, which is distributed in the mountain jungle at an altitude of 980 ~ 1600 meters. Its harm is similar to that of Cuscuta chinensis, but it is mostly harmful in jungles and trees. The whole herb has medicinal value, and has the effects of removing blood stasis, reducing swelling, relieving stranguria and diuresis.

scrophulariaceae

The parasitic life is Striga.

Witchweed is an annual semi-parasitic herb, commonly known as fire grass and dwarf grass, with about 23 species, mostly distributed in tropical and subtropical regions of Asia, Africa and Oceania. Its main hosts are monocotyledonous grasses, such as corn, sugarcane, rice, sorghum, Sudan grass and thrush. A small number of monocotyledonous herbs can be parasitic on dicotyledonous plants, such as tomatoes, kidney beans, tobacco and sunflowers. There are 3 species 1 varieties in China. Yellow bristles grow on the stems of one-legged gold; Leaves are long and narrow, lanceolate and often degenerate into scales, about 65438±0cm long. The lower part is opposite and the upper part is alternate, with a little chlorophyll. Flowers are solitary in leaf axils, and the top is unfamiliar with spikes. Corolla tubular, about 1 ~ 15cm long, longitudinal edge10,5-lobed, corolla yellow. Capsule ovoid, dehiscent, about 3 mm long, tiny seeds, golden oval, with reticular longitudinal lines or ridges. When it matures, it flies away with the wind and falls into the soil. Seeds can survive in soil 10 ~ 20 years. After dormancy 1 ~ 2 years, it germinated at 30 ~ 35℃ under the stimulation of host root exudates. A person's feet have chlorophyll which can be used for photosynthesis to make food, but it is still not self-sufficient. After the host was injured, its growth was blocked and it was delicate and lifeless. Corn production is reduced by 20% ~ 60%, especially in dry years. If corn is planted in the disaster-stricken area for six years, it may be useless. The warm and humid ecological environment is suitable for the growth of Polygonum multiflorum Thunb. The whole herb can be used as medicine, and it has the effects of removing fire, reducing swelling and treating infantile malnutrition.

Morphological characteristics of various wild herbs

1. Aegilops tauschii; 2. The corolla of wild pea is unfolded; 3. Gynura divaricata pistil; 4 ~ 5. Stamens of wild shrews; 6. Cross section of the ovary of Zizania latifolia; 7. Wild fruit; 8. Wild seeds; 9. Brazilian berries. )Walp。 ; 10. The lower section of the ovary of Ranunculus brevicaudatus (showing that the ovary is incomplete due to the combination of placenta; 1 1. 12. Flower Survey of Toona sinensis in China (Imitating Wang Wencai: Flora of China, Volume 69)

Some plants, such as cotton, broad beans, flax, soybeans and so on. , can stimulate the seed germination of one foot, but they are not hosts and cannot establish parasitic relationship. These plants are called "induced plants", and they are often used to induce the seeds of a person's feet to germinate in production to reduce the density of parasites in the soil.

Santalaceae

Usually herbs or shrubs, rare small trees, some semi-parasitic, some completely parasitic or seriously parasitic plants. Simple leaves, alternate or opposite, a few reduced to scales, no stipules. Flowers bisexual, usually dioecious, umbels or panicles or spikes, some single flowers axillary, bracts usually attached to pedicels. Ovary inferior, 1 ~ 3 ovule, without integument, drupe or nutlet, fleshy exocarp, endocarp bone, 1 seed, without seed coat. About 30 genera and more than 400 species, mainly distributed in tropics and subtropics, with a few distributed in temperate zones. There are 8 genera and 35 species in China. Sandalwood is a famous and valuable perfume plant, and parasitic vines and heavy parasites are important parasitic plants.

Parasitic vine

Tree nutrition

There are 25 species in this genus, most of which are semi-parasitic woody lianas. They have no thorns, but alternate leathery leaves and chlorophyll. It is mainly distributed in hillside forests at an altitude of 400 ~ 365,438+000 meters, and its hosts are mostly broad-leaved trees such as oak. Veins 3 ~ 9, basal, arc-shaped. Umbrella or umbel, solitary flower, drupe.

Severe parasitism

Phacellaria

There are 7 species in this genus, all of which are parasitic woody plants. In fact, they have no stems and leaves, but wooden pedicels are often mistaken for stems, unbranched, clustered on the host, 6 ~ 8 cm long, unisexual flowers, usually monoecious; Drupe, fleshy exocarp and bony endocarp are typical super parasitic phenomena. Most of the hosts are parasitic plants, mainly COLEOPTERA, parasitic family and mistletoe family, and a few can be parasitic on parasitic vines.

Prevention and treatment

The control methods of parasitic higher plants vary with the species of parasites. Among woody plants, semi-parasitic or heavy parasitic plants are usually cut down artificially to remove parasites to prevent them from flowering and fruiting, and chemical agents can also be used to prevent them, but it is not easy to completely eliminate them in forest areas. In addition to manual control, chemical control methods such as spraying herbicides, crop rotation control or biological pesticides can be used to control parasites completely parasitic on crops.

philology

Wu Zhengyi et al., Flora of China, Science Press, Beijing, 1977 ~ 1990.