Heavy snow falls under a bright northern sun, and with such changeable weather, beware of catching a cold
Spring is the world of flowers - this may be a common line in many people's elementary school essays. In reality, there really are many kinds of plants that bloom in spring. Not to mention wild plants in the mountains and fields, even in urban landscaping, spring flowers are dazzling, such as the Rosaceae family that confuses people every year, and the three sisters: winter jasmine, forsythia, and golden bell flower.
In many northern cities, spring brings not only trees that bloom, but also a kind of tree that drops "caterpillars" and "floats snow" ----Chinese white poplar（Populus×tomentosa）。
In the warm spring season, people bundle up as tightly as in winter. Image: ImagineChina
The fear of being dominated by "caterpillars"
The Chinese white poplar is one of the mainstreet trees in northern Chinese cities. Every March, the Chinese white poplar, which has been bare all winter, begins to constantly drop onto the groundreddish-brown "caterpillars". As a mischievous little boy when I was young, my favorite thing to do was pick up these "caterpillars" and throw them at my female classmates, collecting their screams. Of course, this was just a clumsy way for a little boy to get a little girl's attention, and it is not worth learning from.
These not-at-all-dangerous "caterpillars" are actually the dried and fallenmale inflorescencesof the male Chinese white poplar after they have dispersed their pollen. They are part of the plant body and have nothing to do with animals.
Male inflorescences of the Chinese white poplar shedding pollen. Image: I don't know plants
The Chinese white poplar has adioeciousbreeding system. Male plants have only male flowers; the male flowers without a perianth form catkins [tí], and the red anthers crack open when mature,dispersing pollen into the wind. Female plants have only female flowers, which also form catkins without a perianth. The stigma of each female flower is split in two, extending into the air in the hope of receiving pollen carried by the wind.
Two male flowers of the Chinese white poplar; you can see the red anthers and the bracts with long hairs, but there is no perianth. Image: I don't know plants
After the male plant's catkins have dispersed their pollen, they no longer serve any purpose and thendry up and fall off; while the female plant's catkins enter thefruit developmentstage after pollination. The inflorescence axis elongates, the ovary of the female flower swells, the stigma shrivels, and the fruit cracks open when mature, spreading the seeds.
After pollination, it enters the fruit development stage; the ovary begins to swell, and the inflorescence axis begins to elongate. Image: I don't know plants
The seeds of the Chinese white poplar are tiny and bear cotton-like appendages, dancing in the wind and carrying the seeds into the distance. Because of the cotton-like hairs, every seed-dispersal season brings"snow" flying all over the sky, a truly spectacular scene.
The yellow ones in the picture are seeds of P. purdomii, with very abundant cotton-like hairs that help the seeds spread by wind. Image: I don't know plants
"Floating snow" is everyone's nightmare
The trunk of the Chinese white poplar is straight and can reach up to 30 m tall. As the tree ages, the bark changes from dark gray to grayish green, and finally to grayish white, while the base of the trunk turns black when old.
The grayish-green bark shows that this Chinese white poplar planted in urban landscaping is not yet very old. Image: I don't know plants
The propagation technology of the Chinese white poplar is relatively easy; sowing, cuttings, or grafting can all be used for seedling raising and afforestation. As afast-growingtree species, the Chinese white poplar can reach usable timber in 20 years under sufficient water and fertilizer conditions, and its growthadaptability is very strong; it can grow on clay, loam, sandy soil, and even slightly salinized soil.
Because of these excellent traits, the Chinese white poplar occupies the main position among street trees in many northern cities, and it also brought childhood joy to many people, such as me.
A tree full of "caterpillars" is about to fall; who knows how many people it can scare again. Image: I don't know plants
However, because the Chinese white poplar iswind-pollinated, during the flowering stage the pollen drifting in the wind brings many people themisery of allergies. For people who cannot leave the allergen for various reasons, a mask is the most important way to prevent pollen allergies. The poplar catkins flying all over the sky also bring great trouble to maintaining urban sanitation.
The mystery of the Chinese white poplar's origins
The Chinese white poplar is a member of the genus Populus in the family Salicaceae. There are about 100 species of Populus in the world, and China has 71 species, of which 47 are endemic species, and at least 10 are hybrids.
The phylogenetic taxonomy of Populus still seems somewhat chaotic. This is because hybridization among species within the genus occurs from time to time, and there area large number of natural hybrid individuals; these hybrid individuals then form even more complex hybridization relationships with other species. In order to better complete the research, researchers are observing wild populations more deeply, collecting more samples, and integrating more research methods.
Chinese white poplarThe multiplication sign in the middle of its scientific nameindicates that it is not an independent species, but one of those 10 natural hybrids. When people first published the Chinese white poplar, they did not yet know its natural hybrid identity, so there was no multiplication sign in its scientific name at that time. As research deepened, researchers found that the Chinese white poplar is related to more than one other species in the genus Populus, and therefore speculated that it should be a hybrid, and then began the work of searching for the parental species of the Chinese white poplar.
Early on, some people proposed that the bract morphology of the Chinese white poplar is very similar to that of P. x canescens, and speculated that the Chinese white poplar might be a hybrid offspring of P. x canescens and P. tremula. Later, some speculated that P. davidiana and P. alba var. pyramidalis participated in the formation of the Chinese white poplar, while others believed that the Chinese white poplar is a natural hybrid offspring of P. alba and P. adenopoda.
To date, there have already beenmore than ten published routes for the hybrid origin of the Chinese white poplar, but there is still quite a way to go before the mysterious veil over the Chinese white poplar's origins is finally lifted. At present, evidence from molecular systematics shows that P. adenopoda is most likely the maternal parent provider in the formation of the Chinese white poplar, while other poplars provided pollen (the paternal parent) during the hybridization process. The specific hybridization process still requires further research to reveal; in any case, it is avery complexprocess.
Do you still recognize the character "yang"? Image: Georges Seguin & AnRo0002 & Daniel Dumais / wikimedia
In recent years, air pollution problems (such as smog) have been relatively prominent, and the Chinese white poplar, as a main street tree, was once again discovered by researchers for a shining quality - absorbing and retaining PM2.5 particles through its leaves. Although from the data, the Chinese white poplarcannot yet become the main force in preventing smog and reducing haze, it still brings us new ideas for research.
Because of its own advantages, the Chinese white poplar has become a common native plant in the wild in North China, while also occupying space in human settlements and bringing researchers many research directions. From the population and genetic level, the Chinese white poplar has not yet come under survival pressure.
But we should not forget that the survival of a species is inseparable from the environment in which it lives. Only when the environment is well protected can the various species living within it also receive practical and effective protection, including humans themselves, of course.
This is the 249th article of the 4th year of Species Calendar, from Species Calendar author @I don't know plants.
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