If you visit a botanical garden, you'll surely be captivated by the diverse and vibrant flowers. Every spring, the countless blossoms, large and small, blooming in the fields, hillsides, courtyards, and roadsides, carried by the warm spring breeze, are always the most palpable signs of spring. As a species living in the new generation, humankind is fortunate. We not only enjoy the food provided by various plants but also the beauty that flowers bring. Therefore, since ancient times, humans have been exceptionally interested in flowers. In the hands of artists and the chisels of sculptors, flowers have always been a subject of depiction and carving; in the works of poets and writers, there are endless verses praising flowers. For botanists, flowers are also a key focus of their research, even being used as a taxonomic term—the name "flowering plant" has long been synonymous with seed plants, encompassing both gymnosperms and angiosperms.
The term "flowering plant" refers to the presence of a "tepal" or "sporophyllum," but in reality, ferns already possess a podophyllum, while gymnosperms do not. Therefore, strictly speaking, "flowering plant" does not truly represent seed plants, and this term has gradually fallen out of use. However, it is precisely because angiosperms possess true perianths that flowers have become their most important organ, distinguishing them from other plants. Thus, when people think of flowers, they often think of this large group classified as angiosperms by botanists. Moreover, it is precisely because angiosperms possess various advanced characteristics, including the advanced flower, that they have become the most dominant group in the plant kingdom from the Cenozoic Era to the modern era. It can be said that angiosperms are the best among flowering plants, and indeed, the best in the entire plant kingdom.
So, what makes angiosperms stand out?
Like gymnosperms, angiosperms reproduce sexually using seeds. The difference lies in their reproductive mechanisms. In gymnosperms, the megasporangia (ovules) are naked, and the resulting seeds are also naked. In angiosperms, the ovules are enclosed in the ovary. The ovule develops into a seed, and the ovary develops into a fruit, with the seed enclosed within the fruit. This difference is the most significant distinction between these two groups of plants, thus giving rise to their respective names: gymnosperms and angiosperms. This difference itself reflects the more advanced characteristic of angiosperms compared to gymnosperms—protected seeds are more conducive to dispersal and the development of a new generation of plants.
In addition, angiosperms have a number of other advancements.
As reproductive organs, the sporophyll cones of gymnosperms resemble their flowers, but they are far more primitive than those of angiosperms. They typically consist of either only pistils or only stamens, usually just spherical aggregates of fruit scales (like pine cones). During the Permian period, some gymnosperms also possessed perianths, but these were much simpler than those of angiosperms. Angiosperm flowers originated from the sporophyll cones of gymnosperms, but were far more advanced. A typical angiosperm flower consists of a calyx, corolla (together called the perianth), stamens, and pistil. The corolla is composed of petals, which are formed from the degeneration of small sporophyll leaves. The cells of the petals contain various anthocyanins and aromatic oils, giving the flowers their vibrant colors, rich hues, and fragrant aroma. The base of the petals also contains nectar glands that secrete sweet and fragrant sap, further enhancing the flower's fragrance. The vibrant colors and fragrant aromas of flowers attract various insects. As insects search for, gather, or absorb nutrients from the flowers, they pollinate the plants. This provides an effective alternative to wind pollination in the sexual reproduction process of plants. This pathway embodies the establishment of a mutually beneficial relationship between plants and insects, enabling them to co-evolve. On the one hand, it greatly increases biodiversity in the ecosystem; on the other hand, it opens up broader avenues for the evolution and development of both angiosperms and insects.
Furthermore, angiosperms have demonstrated progress in many processes of heredity and development, as well as in the structure of stems and leaves.
