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After plants blossom and bear fruit, they always try their best to "throw" the seeds and fruits elsewhere, so that they can stand on their own feet when they fall to the ground.

Mangrove | Picture Source: Wikipedia however, there is such a group of plant babies in nature who can't wait to sprout in their mother's arms before they land. Just as an animal fertilized egg develops into a fetus in the mother's belly, the phenomenon that these seeds germinate directly on the mother is also called vivipary (also known as fetal sprouting).

Viviparity is not common in plants, but it can be seen everywhere in tropical and subtropical mangroves. About 1/3 of mangrove plants are viviparous.

American mangrove (Rhizophora mangle) vivid vegetative form | Source: the candle-like "fruit" hanging from the Wikipedia mangrove is not actually their fruit, but a viviparous vegetative form formed by the elongation of the Hypocotyl after the seeds germinate in the fruit. While absorbing nutrients from their mothers, they rely on their own chloroplasts for photosynthesis.

When the reproductive form germinates to a certain stage on the mother tree, it will fall to the ground like an arrow and take root. Some propagules grow to half a meter long on the tree before leaving their mother, which can be said to be a "giant baby".

The long Hypocotyl of the reproductive body of the total flower mangrove (Rhizophora racemosa) | Picture Source: Wikimedia Commons plant viviparous is divided into apparent viviparous and cryptofetal, the former you can see that the seeds still on the tree sprout through the seed coat, pericarp, obviously protruding from the fruit, while the latter is quietly germinating in the fruit, which can only be seen by cutting.

In mangroves, 8 genera are viviparous as the main mode of reproduction, among which 4 genera of mangrove family are typical viviparous plants, including Rhizophora, Kandelia, Ceriops and Bruguiera.

The process of breaking through the seed coat of viviparous mangroves and Kandelia canadensis | Source: DOI: 10.17521 / cjpe.2016.0087 the other four genera that do not belong to the mangrove family are cryptofetal, including Avicennia, Aegiceras, Nypa and Pelliciera.

Why do the plants in these mangroves choose such a strange way of "laying babies"?

I'm afraid the plants themselves have no choice. They live in the coastal intertidal zone where conditions are harsh, and only the fittest can survive.

The intertidal zone ebbs and flows every day, and the roots of mangroves are soaked in sea water for a long time. The flooded roots do not breathe well, and the salt concentration of the sea water is very high, so that inland plants can be soaked in such a salt bath every day, and you can harvest a batch of "pickles".

Mangrove roots Wikipedia while mangroves learn to "stand on tiptoe" in such places, their well-developed roots rise high and protrude bamboo shoots-like breathing roots from the ground. Their tissue cells can also filter out salt and prevent themselves from being salted to death.

Mangrove ground is full of breathing roots | Picture Source: Wikipedia mature mangroves can cope with the sea environment, but the little ones are not necessarily. Just as animal viviparity has an advantage over egg birth, the reproductive body that first develops on the mother has a higher starting point than the seed when it leaves the mother. On the one hand, the Hypocotyl of the propagation body has been relatively mature, and the long and developed Hypocotyl has a greater probability that it can be directly into the beach and take root smoothly; on the other hand, the propagation body has been connected with the mother for a long time, inheriting the salt ion concentration of the mother, it is easier to adapt to the environment where the mother is, and even drifting may survive for dozens of days.

Mangrove seedlings | Picture Source: Pixabay most plant seeds do not germinate until they find a suitable environment, or they will dormant, just like ancient lotus seeds for thousands of years. The seeds of viviparous plants do not have dormancy, and they must quickly begin to face the harsh environment. The length of dormancy period is regulated by hormones. Abscisic acid (ABA) is a hormone that promotes plant dormancy and inhibits germination. The concentration of abscisic acid in viviparous mangrove embryos is lower than that in general plants.

The water content of ordinary plant seeds will drop to about 8% during the dormant period, while the seeds of viviparous plants always maintain high water content. After all, water is also a necessary condition for germination.

A small number of cactus plants that live on the beach also use viviparity, allowing the seeds to stay temporarily in the "ivory tower" of the fruit and then become independent after germination.

Viviparity of cactus (top: Ferocactus herrerae, bottom: Stenocereus alamosensis) | Source: Cota- S á nchez et al. (2007) common crops also have viviparity in special environments, such as corn, rice, strawberries and tomatoes.

Viviparous dominance of tomato, sweet pepper and grapefruit | Source: Cota-S á nchez, J. H. (2018) this is generally due to the fact that the environment is too humid and warm, and this is what happens when ripe seeds just reach the conditions for germination inside the fruit.

Strawberry seeds germinate directly on the plant | Source: some Wikipedia plants have mutations in dormancy-related genes, so the seeds are no longer dormant, so they germinate directly in the mother. The early germination of crops will affect the harvest and need to be avoided as much as possible.

You may also have heard of the birth of Woodwardia prolifera, the scientific name of this fern.

Inaturalist is not a seed developed from a fertilized egg, nor is it a spore, but a vegetative reproductive structure of a plant, which, like tubers and roots, can be used for asexual reproduction and grow into a new plant just like its mother.

Dioscorea zingiberensis plants such as yam, yellow single leaf axillary long "bean" is also a kind of bulb, each bulb can independently develop into a new plant.

Bulbous buds of Dioscorea zingiberensis (Dioscorea) Wikipedia Commons nutritional structure such as this directly developed into larvae on the mother is not really viviparous, it can only be regarded as "pseudoviviparous" (pseudovivipary).

False viviparity generally occurs when living conditions deteriorate and plants do not have the energy to reproduce sexually, so they just split up and keep their genes first.

This is similar to animals, if life is difficult, it is better to find a partner than to work first.

Reference:

Https://docs.qq.com/doc/DRlBhdWdrVXJNUUJl

This article is from the official Wechat account: take Science Home (ID:steamforkids), Mirror

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