Angiosperms are the largest and most advanced class of plants. Compared with gymnosperms, angiosperms have real flowers, so they are also called flowering plants. So where is the origin of angiosperms? Let's get to know it!
Angiosperms the origin of Lilium angiosperms: proposed by Heer. The reason is that fossil plants of Magnoliaceae and Dryopteridaceae have been found in Greenland. It is believed that flowering plants start from the Arctic Circle and then migrate southward. There are three migration routes: from Europe to Africa; from Eurasia to China and Japan, then southward to Malaysia and Australia; from Canada to Latin America via the United States.
There are two problems with this hypothesis: the polar flora is rather poor in both modern and fossil forms; the poles are changeable, and the present north pole is not necessarily the north pole of the past. The inclination angle between the sun and the earth is now 23 degrees 30 minutes, but in the past it was 35 degrees.
The hypothesis of the origin of the Arctic is considered untenable.
Angiosperms kapok
1、 After the hypothesis of the origin of the tropics (the theory of the origin of the middle and low latitudes) was denied, many ancient angiosperms were preserved in the tropics, which attracted the attention of systematic scholars and put forward the idea of tropical origin. Tahtaj proposed that from Assam in India to Fiji in the southwest Pacific Ocean is the origin center of angiosperms. Smith A. C. believed that the origin center of angiosperms was between Japan and New Zealand, and they all based on the existence of degeneria vitiensis of Magnolia in Fiji. This plant has a monocarp that keeps open before fertilization, which is a relatively primitive character. Chinese scholar Wu Zhengyi also advocated the origin of angiosperms in the tropics. The origin of the tropics has three places:
(1) Tropical Asia: Wu Zhengyi thinks that "the vast area of southern, southwest and Indo China Peninsula in the northern latitude of 20-40 degrees is the temperate and subtropical zone of modern East Asia, and also the beginning and birthplace of temperate flora of North America and Europe". He put forward the theory of the origin of tropical Asia in 1964, and expounded it in more detail in 1977. Before the Tertiary period, the continents of the earth were linked together. In the area of 20-40 degrees north latitude, modern angiosperms are rich, and there are many ancient plants. Angiosperms originated here and transferred to North America and Europe. The migration of the continent resulted in the distribution pattern of modern plants. Takhtajan and Smith's views are as stated earlier. The carpels of degeneria are single and open before fertilization. They are similar to caytonia which belongs to seed fern. But in fact, in the geological history of Fiji, it was a coral island that rose from the sea after the Tertiary period. Its carpel has been reduced to only one. Compared with other plants of Magnoliaceae with multiple whorls and spiral arrangement, it should be said that it has evolved.
Angiosperms -- Mikania
(2) Tropical America: proposed by Thomas, the Amazon basin has the most abundant angiosperms (45000 species) in modern times. However, although the flora of South America is very rich, it lacks the original representation. For example, there is no representative of Hamamelidaceae. The Magnolia genus of China and America is transmitted from North America, which reflects that the flora of South America is not the oldest, and the fossil flora also shows this point.
(3) Tropical Africa: proposed by Devin and Axelrod, according to the plate theory in the 1970s, Africa and South America belonged to Gondwana before the Cretaceous, part of which was called West Gondwana, and the other two, namely Australia Antarctica and India, also belonged to Gondwana. It is said that Africa is rich in fossil flora, but only 15000 species are extant. Relative to the area, the species is poor. Devin thinks that the drought in Africa has caused the lack of species. The islands of the South-East Pacific Ocean, which had drifted out of Gondwana a long time ago, found refuge and preserved abundant species.
The tropical origin of angiosperms is accepted by most people.
Angiosperms Zou Ju
2、 On the origin of subtropics
Professor Zhang Hongda proposed that the viewpoint was formed in 1962 and published in 1980, proposing that "the Cathaysia ancient land was in a relatively stable state at the end of Paleozoic and the whole Mesozoic era, and it may be the cradle of the origin of primitive angiosperms and flowering plants here". Cathaysia flora refers to the floristic flora developed in South China platform and its adjacent areas since Triassic. The name is Harry Halle T. g. it is used in the Paleozoic flora of East Asia represented by bigfeathered fern. Professor Zhang Hongda has extended the meaning of the name. Its scope includes the vast area south of the Yangtze River Valley, the eastern reaches of Jiangsu, Zhejiang, Fujian and Taiwan coastal areas. The western part of the Yangtze River has Sichuan, Kang, Yun, GUI and other platforms. It also includes Tibet and Himalaya mountain areas rising after the third century, and the southern part has two broad areas and adjacent Indochina peninsula. The main reasons are:
1. There are many ancient taxa in angiosperms of the Cathaysian flora, including magnolia, Ranunculaceae, kunlan order, Yunye, Lianxiang, Nymphaeaceae and hamamelis.
2. The angiosperms of the Cathaysian Flora contain a large number of families and orders that play a key role in various stages of phylogeny and their original representatives. These angiosperms are of the order pentaphylla, eucommia, Saxifraga, Violaceae, camellia, Rutaceae, Euonymus, Alisma, Liliaceae and so on, which constitute a complete system. This network of angiosperms is incomparable to any other continent.
Angiosperms sunflower
3. After Mesozoic, the transgression of Cathaysia stopped. Orogeny combined Cathaysia with other ancient lands and became stable. It is most favorable to become the birthplace of flowering plants. The fossil and pollen of various flowering plants have also confirmed this viewpoint. Other ancient lands, whether Australia, Africa, South America or tropical Asia, were either transgressive or covered by glaciers after entering the Mesozoic era, which was very unstable. From the existing flora and the lack of fossil and sporopollen, we can see that they are difficult to become the cradle of flowering plants. If this is not the case, it is impossible to explain the unity of the origin of the plants on all continents of the earth and the particularity of the development of the flora of each continent.