The reason why pine and cypress are evergreen may be because... they react slowly?

Qiān (qiān) is a plant that is both familiar and unfamiliar to most people. It is a member of the genus Picea in the Pinaceae family. The Pinaceae family is the most well-known group of gymnosperms, and its representatives are the various pine trees we often see. According to the academic community, there are 10 to 11 genera and more than 250 species in the Pinaceae family, which are distributed throughout the northern hemisphere. There are more than 30 species of Picea in the world, and nearly half of them are produced in China.

Schematic diagram of the phylogenetic relationships of the genera of Pinaceae.

The Pinaceae family includes both "pine" and "fir". Generally speaking, "pine" has leaves that are slender and grow in bundles, such as various pine trees (Pinus), cedar (Cedrus), larch (Larix), etc. "fir" has leaves that are flat or columnar and grow in spirals on branches, such as fir (Abies), spruce, Keteleeria, etc.

Taiga forest in the Altai Mountains of Xinjiang.

Fir and spruce are widely distributed in the northern hemisphere. In the cold temperate zone, they form vast taiga forests. In the warm temperate zone and subtropical zone, they mainly grow in alpine areas, forming coniferous forests dominated by gymnosperms. As the name "fir" suggests, it likes cold environments, and the name "spruce" means that it grows in misty mountains. The representative species of the spruce genus in the western end of Eurasia is the European spruce (Picea abies). Most of the Christmas trees used by Europeans for Christmas are European spruce.

The Christmas tree is actually the European spruce. Photo: Laura Bittner / wikimedia commons

Notorious for being afraid of heat

Picea meyeri is a native species of Picea in North China. We know that there are large areas of plains in North China, but Picea meyeri does not like to grow on flat ground because it is too hot in summer. Picea meyeri generally chooses mountains with an altitude of more than 1,600 meters, and 2,000 meters is more comfortable. It is distributed in some high mountainous areas in Shanxi and Hebei in North China, such as Wutai Mountain, Guancen Mountain Range (Luya Mountain), northern Taihang Mountain Range (Xiao Wutai Mountain), central Yanshan Mountain Range (Wuling Mountain), etc. In addition, it is also distributed in Inner Mongolia and neighboring areas of Hebei. Picea meyeri has a brother called Picea wilsonii, which also grows in similar environments to it, and sometimes even grows together.

Wild white mulberry.

When I visited Xiaowutai Mountain and Luya Mountain, I saw large areas of wild white elm forests. In recent decades, many forest farms and nature reserves in North China have also used white elm for afforestation, so now it is relatively easy to see white elm in many mountainous areas in Shanxi, Hebei and Beijing.

The white ash forest in Luya Mountain, Shanxi Province.

White mulberry artificially cultivated in the mountainous area of ​​Beijing.

Please pay attention to the character "杄" (not "扦"), which is specifically used for white 杄 and green 杄. It is also used as the place names of some villages in Shanxi and Hebei, such as 杄mugou. I checked on the map and found that 杄mugou is a village in Ningwu County, Shanxi Province, located in Guancen Mountains. Perhaps there are tree species like white 杄 in the mountains near the village, so it got the name.

The reason why pines and cypresses are evergreen

The leaves of the white shrub are arranged in a spiral shape on the branches, like a test tube brush. The leaves are very hard. If you look at it from a cross section, they are quadrangular. The surface of the leaves is covered with obvious white powder, and they look whitish from a distance. The "white" in the name refers to the color of the leaves. In contrast, the leaves of the green shrub have very little white powder and are green, so it is named "green". In addition, the branches of the white shrub are reddish brown and the leaves are relatively sturdy, while the branches of the green shrub are grayish white and the leaves are relatively slender. These characteristics can well distinguish the two.

The branches of white ash (left) and green ash (right).

The leaves of the white pine are hard and slightly curved, with a thick cuticle on the surface. The stomata are regularly arranged in a linear shape on the leaf surface and sunken under the cuticle. This feature can not only protect against cold, but also prevent excessive evaporation of water, so it can adapt to the environment of high-altitude cold areas and remain evergreen all year round. However, this also has a disadvantage: the growth and renewal of leaves are relatively slow, the photosynthetic efficiency is low, and the growth rate of the whole tree is also slow. What we often say about evergreen pines and cypresses refers to the fact that most gymnosperms of the pine and cypress family are evergreen and have a relatively long lifespan.

Different pines have different destinies

However, pine plants also have different strategies for adapting to the cold. For example, larch (Larix) does the opposite. Its leaves are very soft. When the warm growing season arrives every year, it quickly sprouts new leaves. The texture is very thin, and there are many pores on the back, which can exchange gases with the outside world very well. Therefore, it can use the short summer to produce a lot of nutrients, but it cannot resist the severe cold, so when autumn comes, it loses all its leaves to survive the severe winter. But even so, larch produces more nutrients than spruce and fir during the growing season. In comparison, larch grows much faster, so it uses its ability to grow quickly to occupy a place in the dense coniferous forest.

Larch leaves.

The white hollyhock blooms every spring. Of course, it is a gymnosperm and does not have real flowers. The so-called "flower" is a microsporophyll that emits a large amount of pollen, which is spread by the wind. In summer, cylindrical cones are produced, hanging at the end of the branches. They are composed of countless layers of seed scales arranged in a spiral and closely connected. Due to sunlight, the sunny side of the cone often appears purple-red, while the side facing away from the sun is green.

The branches of white poplar are full of cones.

The cones of the white holly (the left side is facing the sun, the right side is facing away from the sun).

The style of spruce is relatively soft, with branches often growing flat or drooping, and cones also drooping, while the style of fir is very hard, with branches usually growing straight and obliquely upward, and cones also standing upright on the branches.

Fir branches and cones.

The cones of the white mulberry tree will mature in the autumn of the same year. When ripe, the entire cone will dry up, and the seed scales that make up the cone will open outward, releasing the seeds inside. Its seeds have wings and can float in the wind. After falling in the right place, they will be able to germinate and grow into seedlings in the next year.

The spruce brothers blocked by the plain

According to biogeographical research, the spruce family originated in North America and then spread to Eurasia. During the glacial period of geological history, this family was once widely distributed in the plains or low-altitude areas of the Northern Hemisphere. Many species were born from the same mother. After the glaciation ended, as the global climate warmed, these low-altitude areas were occupied by other warm-loving plants. The members of the spruce family retreated to some local mountains and migrated to places with higher altitudes or higher latitudes. As a result, the long geological history has caused the isolated distribution of the members of the spruce family. In North China, only the two brothers, the white spruce and the green spruce, are left, while in the northeast, there are fish-scale spruce (Picea jezoensis) and red-skinned spruce (P. koraiensis), and more species retreated to the high mountains in the southwest.

Spruce forests in the southwestern alpine regions.

If you travel to the southwest, such as western Sichuan, Tibet, and northwestern Yunnan, you will definitely see coniferous forests formed by spruce and fir as you drive over snow-capped mountain passes, with deciduous broad-leaved forests below and alpine shrubs and meadows above. Large tracts of forest cover the mountains and stretch endlessly. Various types of spruce produce cones in summer. Due to different species or maturity periods, cones of various colors hang on the branches, which is also a beautiful scenery.

Cones of various spruce species.

The mountain hermit comes down to earth

Nowadays, the white spruce, which lives in the mountains, has also been introduced to the plains. It is often cultivated in botanical gardens or courtyards, and can even bear fruit normally. Its tree shape is upright, and its leaves are pink and green, which has a high ornamental value. In some counties and districts in northern Hebei and Inner Mongolia, due to the high altitude of the county seat and the very cool summer climate, white spruce is also used as a street tree. In recent years, with domestic and foreign exchanges, some botanical gardens or parks have also introduced the blue spruce (Picea pungens) native to North America. Its leaves are densely covered with blue-gray powder, the whole plant is more pink, the leaves are longer and pointed, and the shape of the cones is also different. Compared with it, the white spruce is really not white.

Blue spruce cultivated in Beijing Botanical Garden.

Blue spruce cultivated in Beijing Botanical Garden.

The white spruce, a fairy that descended from the clouds, has entered the lives of ordinary people. Even if you don't climb high mountains, you can still appreciate its graceful figure in the park. However, if you see a particularly pink and white blue spruce, don't mistake it for the white spruce.

This article is the 121st article in the 6th year of the Species Calendar, and is from the Species Calendar author @ArtemisiaLiu.