Cactus is native to North and South America, from British Columbia and Alberta to most parts of the south; Its southern border extends to Chile and Argentina. Mexico has the largest variety of cacti. Only Rhipsalis may be native to the Old World and distributed in East Africa, Madagascar and Sri Lanka. However, many scholars believe that this genus was introduced to these areas from other parts of the world.
Cactus is a succulent perennial. Although a few species live in tropical or subtropical areas, most of them live in arid areas. The stem of cactus is usually thick and contains chlorophyll, grass or wood. Most kinds of leaves either disappear or are extremely degraded, thus reducing the surface area of water loss, while photosynthesis is replaced by stems. Only tropical Pereskia and Pereskopsis have obvious functional cacti. Roots are usually slender, fibrous, shallow and widely distributed, and are used to absorb surface water.
Primitive cactus plants have leaves. They were originally distributed in less arid areas, and their appearance is not much different from that of ordinary plants. Just because of the vicissitudes of life, the originally humid areas have become more and more dry. In order to adapt to the environment and survive, the shape has changed. Normal flat leaves gradually degenerate into cylinders, then become scales, and finally disappear completely. Today, some primitive cacti are distributed in some less arid areas of Central America. Among them, Acanthopanax, Monopterus and Lepidoptera in Julia have normal flat leaves, but their size and meat quality have changed. Cactus leaves are big and thin, and there is basically no meat. In southern China, cactus (also known as eucalyptus angustifolia), the most common species of this genus, can often be seen crawling on the wall, but when it is not flowering, it is often mistaken for bougainvillea, a common flowering shrub in southern China. The leaves of Opuntia grandiflora of this genus are as long as 15 cm. Cactus, red sandalwood, red sandalwood and cactus also have leaves, but they all degenerate into cylindrical shapes, and most of them only grow in the tender part of the stem and fall off quickly. Of course, according to different species and different habitat conditions, the size, shape and life span of these single leaves are very different. The conical leaves of Mai Huna are only 0.4-0.7 cm long, while the cylindrical leaves of drill cactus are 12 cm long, and each leaf can exist for 3-4 years, so it always exists in the upper part of its stem. Except the cactus with leaves mentioned above, other cactus plants have no leaves, but evidence that leaves once existed can still be found. Some experts pointed out that the prickles of cactus are actually developed from axillary buds. Some experts also pointed out that many kinds of cactus, the protrusion below the base of its thorn is equivalent to the leaf base of normal leaves.
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The stem characteristics of primitive cactus with normal flat leaves are also different from those of most species. Some are liana shrubs, and the epidermis of the stems is usually not green, except for the tender parts, most of them are lignified. Some kinds of stems, such as common trees, are very tall and highly lignified, such as Bahia cactus and Moon Desert. Their main stems are 8-9 meters high.
The stems of species with cylindrical leaves are usually unsegmented. For example, the general's stem is 2 meters high, and only one section is upward, while many species of the same genus have flat jointed stems. Although the pig's ear palm (opuntia brasilnsis) has a flat jointed stem, its lignified main stem is very high, and the flat jointed stem is just a twig. However, the woody stems of cactus species with inconspicuous cylindrical leaves does not exist or is inconspicuous. Those species without leaves, because of their photosynthetic function, are mainly borne by stems, so under normal circumstances, the stems are green and will not be lignified. Morphologically, it can be said that no family of plants is as varied as cactus: some are flat as mirrors, some are lampstands and organs, some are overlapping mountains, and some are slender as snakes. Most of them are spherical or nearly spherical, which is the result of long-term adaptation to arid environment. Because of the same volume, the spherical surface area is the smallest and the transpiration is also reduced. So in the whole cactus family, spherical species account for more than half. 199 1 year, the United States published a picture book of cactus, which collected all spherical species, excluding cultivated varieties, hybrid collection and ban Jin types, reaching 1098 species, but as far as the author knows, not all of them were included. People usually call cactus lovers "green thorn fans" or "keeping balls to play", and we can also see the weight of spherical species in cactus.
Prisms and verrucous processes
Except for primitive species, cactus stems are horned. There are only cactus, astragalus membranaceus, lotus and some reeds.
Polygonum, Ranunculus and Ranunculus are usually 3-sided, and other genera and species are more than 4-sided. Among them, the number of sides of spherical species is more, and some species have as many as 120 sides, generally more than 10 sides. This is of great significance to adapt to the arid environment. The origin of many cactus plants has such characteristics: it doesn't rain for a long time every year and it rains heavily for a short time in rainy season. The cactus growing in this environment is shrinking in size due to the continuous loss of water in dry season. Once it rains, it absorbs water to the maximum extent and makes the plant expand rapidly. If the ribs don't stretch like accordion folds, the skin will definitely break. The number and arrangement of edges objectively provide a basis for us to distinguish types, which has certain significance in classification.
In addition to the edge, cactus stems also have verrucous processes. This is a unique structure. In fact, in many spherical species, even without obvious verrucous processes, there are transverse tumor-like segments on the longitudinal edge, such as Aralia, gymnosperms, Echinococcus, Leptospira and so on. Verrucous process is the result of further development of these plants adapting to arid environment. With verrucous protrusions, it is more convenient for plants to stretch and dissipate heat. The small bulb of mastoid is attached to the axil of wart, and the tender bulb can be protected by wart and the thorn at the tip of wart to avoid sun exposure and animal damage. Therefore, at present, all taxonomists believe that the genus with obvious wart process is the most evolved species in cactus family.
According to different species, the shape, length, diameter and texture of verrucous processes are quite different. The pyramid-shaped wart in Huangshan is 12 cm long, while the villain hat in the moon world is only 0.2 cm long. Wu Yuyu, Venus and Neptune have soft wart processes, while Poirot's pontine process is hard. The species of Quercus are arranged in a rosette shape, and the sunlight can be fully seen in each process. The fertile soil of Huangshan Mountain is clustered at the end of the stem like agave. However, the wart processes such as the hope ball and the broken piano ball of the mastoid genus are strictly arranged in a logarithmic spiral shape around the growing point, and the pattern is perfect from above. The shape, size and arrangement of this wart are a basis for people's classification.
Thorn seat, thorn and hair
Spine seat is a unique organ of cactus plants. Essentially, the thorn base is a short branch with abnormal height, which looks like a cushion structure on the surface. There are many kinds of buds on the thorn base, including leaf buds, flower buds and adventitious buds, so not only thorns and hairs grow on the thorn base, but also flowers, bulbs and branches grow on the thorn base. The size and arrangement of thorn seats are different. The spinous process of Saturn's crown, a columnar species, is as big as 20 cm, while the spinous process of the moon world and small truffle jade is only 0.2 cm. Most kinds of thorns are round or oval, with a certain distance between them, while the thorns of Baiyun Pavilion and Uber Ball are long and connected end to end on the edge.
Sutures are generally distributed on the stem. However, some species also have thorns in roots, flower receptacles, ovaries and fruits.
Spine is of great significance to the survival of cactus plants and is the product of a protective mechanism. The number, arrangement, color and shape of thorns vary endlessly, giving people beautiful enjoyment. It is also an important basis for species identification and classification. The main shapes of thorns are cone, head, hook, anchor, comb and feather. According to the position of the thorn on the thorn base, there are middle thorns and lateral thorns (peripheral thorns), and the middle thorns are generally stronger. The length of the thorn varies greatly. Many kinds of echinococcosis are about 12 cm long, and one kind of echinococcosis in Colorado is 22 cm long. But there are also many kinds of thorns that have completely degenerated or left only traces, such as planets, jet, truffle jade and so on. Some species have strong spines, but in cultivation, people have cultivated spineless varieties, such as spineless commander, spineless crested dragon, naked beard and so on. Put them together with primitive species to form a sharp contrast. The other two kinds of thorns are often mistaken for hair. One is bristles, which are thinner than needle-like thorns. Although they are flexible, they are flexible. The other is barb, which is very short and dense, with sheath at the base and barb at the top, which is difficult to find. People are easy to get stuck when they are not paying attention, so it is difficult to remove them. Fortunately, this barb exists only in some species.
Hair also grows from the base of thorns, with different lengths and thicknesses, and various colors, and the top never hooks. Species growing at high altitudes are usually covered with long hair, including white-haired Weng Zhu, Weng Jin, eagle Weng and orangutan Weng, yellow-haired Jin, Qicai He and even red-headed skyscrapers with red hair. These long hairs effectively protect plants from intense ultraviolet rays on high mountains. There is also a short and dense velvety hair, usually called felt hair. In some areas with little rain and fog, it can also protect the epidermis and collect dew for the roots to absorb.
Flowers, fruits and seeds
(1) Flowers: Every cactus can blossom. Many varieties can blossom quickly as long as they are cultivated properly. For example, in the future, the species of players will only need three years from sowing to flowering. Culturally, grafting can also blossom in advance.
Flowers are usually planted on thorns. However, the flower and thorn base of mastoid bulb are not in the same position. This cactus usually blooms on mature flaky stems that are completely exposed to the sun. Tall cactus columns can be opened from the middle of the stem to the near top, and strangely, flowers often spread out on one or several edges, but there are no flowers on the adjacent edges.
Many species can produce a large number of flowers at a time. County flower, snake whip column, celestial ruler, cactus (commonly known as grass ball) also have such characteristics when they bloom, that is, when they don't bloom, they can bloom dozens or more at the same time, but strangely, the time and size of flower buds are obviously uneven, but they can bloom at the same time.
However, there are also many varieties that don't bloom very much in cultivation. Although it blooms every year, it only blooms one or two. Such as Huangshan Mountain and Guang Lin Ball. Some varieties have not seen flowers for decades, because some varieties mature late, the cultivation conditions are insufficient or the methods are problematic. For example, Weng Jin of Pyrola, the literature says that flowers are beautiful and long, but they can't be seen after decades of planting. It turns out that flowering must meet two conditions: first, old plants can blossom; Second, high temperature and sufficient ultraviolet rays are needed in winter.
Flowers are usually radiation symmetric. Shapes are funnel-shaped, trumpet-shaped, high-legged dish-shaped, cup-shaped and so on. A few genera and species have symmetrical flowers, such as crab claw orchid, corolla column and snow blowing column. Petals usually have only one or two layers. At present, Stylosanthes hybrid has produced many kinds of double flowers, but it is still introduced in China. Petals are usually entire, and only a few kinds of petals, such as ridgelet, have eyelash-like edges.
Besides true blue and black, there are various colors, and they are ever-changing. It is also a red flower, and its color is different for different kinds. Many kinds of petals have metallic luster and are very eye-catching. Many kinds of pistil stigma and stamen filaments are brightly colored, especially some kinds of cornucopia and southern jade. The stigma is blue and purple, with velvet luster, which is very beautiful in contrast with the petals.
The flowering period is most concentrated in March-May, and there are not many kinds of flowers in autumn, but many kinds can be grafted in spring to make them bloom in autumn. Crab claw orchid, fairy finger, phoenix-winged peacock, jade swan, white star, white amber, snow moon flower and the ball from the sun bloom in the middle of winter, bringing a lot of vitality to the cold and dreary winter.
(2) Fruits: Fruits are generally fleshy berries, and a few are dried fruits. Shapes are pear-shaped, round and rod-shaped. There are thorns or scales on the peel. Many kinds of fruits are beautiful, such as ridges and new bridges; The fruit of the measuring ruler is big and red, and the fruit of the beautiful Wolong column and the single-thorn measuring ruler is lemon yellow. The fruit of the silver dragon is dark blue, shaped like a jar, and the flower-shaped lid with handle (figure 1) is really lifelike and breathtaking.
Some big fruits are edible. The fruits of Tianzhi, Lingjianlian, Wolongzhu and many cactus species can not only be eaten, but also induce diuresis.
(3) Seeds: There are many shapes, generally round, oval and oblate. The seeds of Astra are helmet-shaped, also called bowl-shaped. Stylosanthes seeds are hollow cylinders, also called sleeping bags. The seeds of other columnar species are mostly kidney-shaped. Seeds of Pterocarya have cork-shaped wings. It's weird.
The number of seeds per fruit varies greatly, ranging from thousands to more than ten. The size of seeds varies greatly. The seed size of cactus is 5-6 mm, and each 1000 grain weighs 20 g. However, the dry grain weight of chrysanthemum seeds is only 0.1g.
root
Except for a few arbor-shaped cacti and cacti, the roots of cacti have no obvious main roots, and the lateral roots extend far away and are distributed in shallow soil. The roots of some species can extend 30 meters, which is also an adaptation to arid habitats. Due to the occasional heavy rain when the rainy season comes, the soil water retention capacity is poor, and the cactus with such a wide distribution of roots can quickly absorb enough water for later use in a short time.
Some species have swollen fleshy roots or tuberous roots. In these species, roots replace stems as the main organs for storing water. These species are mainly concentrated in Lithocarpus, Echinococcus, Pterocarya, Rhizopus and some cacti, among which Rhizopus Kochiae weighs 75 kg.
Epiphytic type, such as inchworm, jade willow, etc. There are a lot of air roots on the deformed stem. Air roots have two functions: climbing and absorption. In the place of origin, the main purpose is to let the stem extend along the rock wall of the branch to a sunny place. Once it comes into contact with humus and places with good moisture, aerial roots without root hairs will quickly grow root hairs for absorption. It is not difficult to find that when the root system of inchworm is destroyed or the basin soil is seriously short of water, a large number of air roots appear at the stem node-1. When the ruler is placed in an excessively shady place, the air roots will also climb up along the wooden columns, walls and even glass in the greenhouse.
Because the country of origin has a dry season every year, and the strong sunshine makes the soil surface temperature very high. Therefore, many kinds of root epidermis are cork. The thick woody root layer protects the internal tissues of roots from high temperature damage and prevents water loss. Once it rains, the capillary roots will quickly pass through the cork layer for absorption.
The species of Rhizopus, Pterocarya and Cactus have big round fans with thorns at the roots. The cut root segments can grow into new plants.
Succulents Except cactus, many succulents are related to more than 50 families, and their forms are more colorful on the whole. Compared with cactus, succulents have the following characteristics:
① The species with leaves account for a considerable proportion.
② The characteristics of thorns are not as distinct as cactus. Although many species have strong thorns, they are covered with leaves, and the thorns will only stand out when the leaves fall.
③ Flowers are solitary, but a large part of them blend with various inflorescences. Generally speaking, the ornamental value of flowers is not as good as cactus.
According to the different parts of water storage tissues in plants, succulents can be divided into three types: leaf succulents, stem succulents and stem succulents.
1. leafy plants
Water storage tissues are mainly in leaves. Stems are generally not fleshy, and some stems are slightly lignified. According to the different drought degree of habitat, the meat quality of leaves is also different. The leaves of native species in areas with low drought are bigger and thinner. For example, Eupatorium odoratum (also known as Eupatorium adenophorum, scientific name aptenia cordifolia) is native to natal province, South Africa, and belongs to humid areas compared with other parts of South Africa. So its shape is a creeping plant with large and thin leaves, and its shape is not much different from that of ordinary grass flowers. As the environment tends to be dry, the stems become shorter and the leaves become thicker. Among the apricot species distributed in extremely arid areas, the whole plant consists of only one or two pairs of leaves, the stems have all disappeared, and the leaves are highly fleshy.
Due to the difference of families and genera, although the leaves of leafy succulents have the same xerophytic structure-leaf thickness, cuticle, ash quilt and so on. There are quite a few kinds of leaves. This diversified leaf shape is an important basis for classification. Most of them are simple leaves, but many of them are compound leaves.
There are three kinds of compound leaves, palmately compound leaves, once pinnate compound leaves and twice pinnate compound leaves. The shapes of single leaves are linear, thin cylindrical, spoon-shaped, oval, heart-shaped, sword-shaped, tongue-shaped and diamond-shaped. The leaf margin is mostly entire, and some leaf margins and tips have teeth, hairs or thorns. Some kinds of leaves are transparent at the top, commonly known as windows.
The arrangement of leaves is alternate, opposite, alternate and opposite, rotation, two rows of overlapping cattle, clumping and so on. The leaves of native tree species in higher altitude areas are arranged in a rosette shape, and the whole plant type is very compact, which is an ideal tree species for family cultivation and ornamental. A highly fleshy species of Apricot family, the whole plant often has only a pair of leaves connected to form a solution, which is spherical, oblate, gyro-shaped and ingot-shaped. Because of its variety and small plant shape, it is currently a "hot spot" for domestic succulent lovers to collect and cultivate.
2. succulent plants with stems
The succulents of Euphorbiaceae, Lamiaceae, Apocynaceae and Crotalaria are called stem succulents. Many of these plants have cylindrical or spherical stems similar to cactus, and some have edges and warty protrusions, but they never have thorns, although some species have thorns. Thorns can be divided into skin thorns, acupuncture and thorns, and a few kinds of thorns are very strong, such as Castanopsis species of Araceae, Araceae and Apocynaceae.
Many species with stout fleshy stems usually have no leaves, and some have tiny leaves in young parts but often fall off. The cactus of Compositae is leafy in the growing period and leafy in the dormant period. Fig. 5: Species of succulents wither and fall off. However, Portulaca oleracea of Portulaceae and Swallow's paw of Sedum have stout stems and leaves, and these leaves have always existed.
3. The fleshy part of succulents with stems is mainly at the base of stems, forming extremely swollen blocks, spheroids or bottles with different shapes. There are no knots and edges, but there are verrucous protrusions. Leaves or deciduous early, most leaves grow directly from the root neck or from the slender branches that suddenly become thin and almost meatless. In the extremely dry season, such branches and leaves fall off together, such as the famous succulent species Dioscorea, Guijialong, Guijialong in Mexico and so on.
However, some species have almost normal branches on the swollen stems, and the stems are usually high, and there are leaves on the branches during the growth period, and the leaves fall off but branches exist during the drought dormancy period. On the whole, the plant shape is similar to that of ordinary trees, but the trunk becomes larger and stores more water. Such as baobab and spindle trees of kapok family, elephant-footed trees of Moringa family, elephant-trunk trees of Lacqueraceae family, Queensland bottle trees of Platanus family, desert rose varieties of Apocynaceae in Cautrat, etc. However, it is usually difficult for such cuttings to form swollen stems. The situation of sowing seedlings is a little better, but the morphology of plants growing in humid areas is not typical of citrus plants of origin anyway.
Many herbs have bulbs, which are swollen and grow underground or near the ground. According to the principle of stem base enlargement, they should also be included in succulents with stems. However, some experts do not admit it, so it is controversial whether the species of Saxifraga in Amaryllidaceae and Jujube in Liliaceae are succulents. However, some bulbous plants are absolutely uncontroversial. For example, Cang Jiao Dian and Da Cang Jiao Dian of Lily are famous succulents and treasures that lovers dream of.
4. Reproductive organs of succulent plants
No matter how different the morphology of plants is from that of ordinary plants, the morphology of reproductive organs of succulents is not too different from that of other plants belonging to the same family.
Except for Annonaceae, Apocynaceae and Convolvulaceae, the flowers of most succulents are not as gorgeous as cacti. But it is more diverse in form.
Except for the species of annonaceae, which are solitary flowers, other families are basically planted on plants with various inflorescences. Inflorescences are terminal and axillary, and sometimes there are differences between terminal and axillary plants in the same family and genus, such as kale in Sedum. A single flower is relatively large, while flowers with integrated inflorescences are usually smaller. There are many kinds of inflorescences, including heads (Compositae), spikes (Zanthoxylum), racemes or panicles (Agavaceae), umbels (Rosaceae), cup-shaped cymes (facing the DPRK), dichotomous cymes (Jatropha) and so on. Flowers of Apocynaceae, Labiatae, Rosaceae, Sesamaceae and Convolvulaceae have long tubes, petals are combined and divided, and flowers vary in size and shape. The specific content will be introduced in the classification section.
Fruit types include berries, capsules, drupes, yingying fruits and achenes. Caryophyllum of Araliaceae is the most distinctive, while Cucurbita pepo of Aloe of Liliaceae is very large and interesting. The size and shape of seeds also vary greatly with families, genera and species. The seeds of Annonaceae are very small, while those of Anemarrhenaceae and Araceae are relatively large. The seeds of compositae are like needles, while the seeds of aloe have disc-shaped wings like straw hats. Relatively speaking, succulents are more difficult to collect seeds than cacti, and the varieties that foreign seed companies can provide are far less than cacti.
Physiological characteristics and others
The physiological characteristics of these plants are manifested in several aspects, and generally speaking, they are also caused by arid environment.
First of all, their morphology and some structures of epidermis greatly reduce their transpiration. Their cuticles are thick, and many kinds of cuticles are coated with wax. The number of stomata is much less than that of other plants, and they are deeply buried in pits with sunken epidermis. The diffusion resistance of stratum corneum is great, so this kind of plants lose less water than other plants. The data shows that a corn loses 3-4 liters of water a day, while a tree-like cactus loses only 25 ml of water a day.
Many species have white milk or colorless mucus, which is a polysaccharide. Some experts pointed out that their cells contain a lot of pentose, which increases the concentration of cell fluid and enhances drought resistance and stress resistance. At the same time, this mucus and milk can make the wound conjunctiva heal quickly when plants are injured, which not only prevents water loss in the body but also avoids bacterial infection. Using this feature in culture, some spherical and cylindrical species with large cross-sectional area can be cut to the top.
Another feature is that their osmotic pressure is not high, generally between 405.3 and 2026.5 Ganpa (4-20 ATM), while only cactus plants exceed L2 15.9 kPa (12 atm). This figure is far lower than other desert plants. So there are no cactus plants in some desert areas with a lot of soluble salt. This is very important in practice. Don't add high-concentration inorganic fertilizer at one time when applying fertilizer, and don't mix too much salt in the culture soil, otherwise the water in the roots will seep out, causing plants to wilt.
Cactus and succulents are different from ordinary plants in metabolic mode. It is characterized by closed stomata during the day to reduce transpiration and open stomata at night to absorb CO? And within a certain range, the lower the temperature, the CO? The more you concentrate. The absorbed carbon dioxide forms malic acid and is stored in large vacuoles. During the day, apples decarboxylate and release carbon monoxide? In a certain range, the higher the temperature, the faster the decarboxylation. Because this pathway was first discovered in Sedum plants, it is called the metabolic pathway of Sedum acid. This is also an adaptation to the dry environment. This characteristic is used in cultivation, that is, to increase the temperature difference between day and night in greenhouse as much as possible within a certain range, and indoor CO? Concentration, etc. , can accelerate the growth of this kind of plants.
The cactus plants in this section are native to tropical North and South America, tropical Asia and some nearby islands, and some grow in forests. Most species of succulents are native to South Africa, and only a few are distributed in tropical and subtropical areas of other continents, so South Africa is known as the "treasure house of succulents". From the origin and ecological environment, the above plants can be divided into three categories:
Native to tropical and subtropical arid areas or desert areas. Under the condition of extremely dry soil and air, it survives with the help of water stored in stems and leaves.
Originated in tropical and subtropical alpine arid areas. These areas are short of water, with strong sunshine, strong wind and low temperature. Succulent plants are short, and their leaves are mostly rosette-shaped, or densely covered with wax and fluff, so as to reduce the harm of strong wind and strong light in mountainous areas and reduce excessive transpiration.
Native to the tropical rain forest. These species do not grow in soil, but attach themselves to the rocks of tree trunks and shadow valleys. Its ecological habits are close to epiphytic orchids.