What are those plants that look like garlic? Recognize them, beware of poison!

Produced by: Science Popularization China

Author: Zhang Lijun (Wuhan Botanical Garden, Chinese Academy of Sciences)

Producer: China Science Expo

(Photo source: Veer Gallery)

First of all, please identify what plants are in the pictures above?
Answer: These types all look similar and resemble garlic heads. The ones we are most familiar with are the last two, which are the onions and garlic that often appear in the kitchen. The first two may be more familiar to flower lovers, as they are the bulbs of tulips and lilies.

Then the question arises again, which organ of the plant do these parts belong to (roots, stems, leaves, flowers, fruits, seeds)?

Answer: They are all plant stems, but not ordinary stems. They are a kind of modified stem and belong to bulbs.

Today, we will talk to you about those round stems that look like garlic.

Types of stem metamorphosis

As we all know, organ metamorphosis is very common in plants. Specifically, it is the change in organ function caused by environmental influences, which leads to significant variations in morphological structure. Metamorphosis mainly occurs in nutritional organs such as leaves, roots, and stems.

Among them, stems have the most types of metamorphosis, which are divided into underground stem metamorphosis and aboveground stem metamorphosis according to their location. The stem thorns of honey locust, the stem tendrils of grapes, the leaf-like stems of false leaves, etc. are all aboveground stem metamorphosis; the bulbs mentioned at the beginning, as well as corms, tubers, and rhizomes are all metamorphosis of underground stems. Because there are too many contents and it is easy to confuse, there will be a special article to introduce tubers and rhizomes later. Today, we will mainly introduce bulbs and corms similar to them.

Thorns of Gleditsia sinensis

(Image source: provided by the author)

Cucumber stem tendril

(Image source: China Plant Image Library)

The leafy stem of the false leaf tree

(Image source: provided by the author)

What is a Bulb?

A bulb is an underground stem with shortened internodes and fleshy or membranous modified leaves . Onion is a typical representative of bulbous plants. If you cut an onion longitudinally, you can see a flat bulb disk with shortened internodes. The terminal bud on it will develop into an inflorescence in the future. The bulb disk is surrounded by fleshy scale leaves, which store a large amount of nutrients. There are also several membranous scale leaves on the outermost edge for protection, and there are axillary buds in the leaf axils.

The base of the garlic stem also transforms into a bulb disk, and the axillary buds on it develop and swell to become sub-bulbs, which are the garlic cloves we eat.

Cut surfaces of onions and garlic (Image source: Veer Gallery)

Structure and function of bulb

The bulbs store a large amount of nutrients. Through research, scientists have found that lily bulbs have the dual functions of "sink" and "source", playing different roles at different times. Starch is an important storage form of carbohydrates in lily bulbs, often existing in the form of starch granules in tissue cells. Through experimental observations, during the planting and growth period of lilies, the bulbs mainly serve as a "source" to provide energy substances for the growth and development of stems, leaves and flower buds.

Of course, after the leaves unfold, the leaves become the main "source" to provide energy to the two "sinks" - the bulbs and flower buds through photosynthesis, but before flowering, the inflorescence is the main "sink", and after flowering, the new bulbs (small bulbs growing from the base of the bulbs) are the main "sink".

Therefore, from the growth period to the flowering period, the bulb acts as a secondary "source" and a secondary "sink", so the carbohydrates in the bulb are in a dynamic change. From the end of the flowering period to the bulbing period, the bulb becomes the main "sink" and accumulates starch in the form of new bulbs.

Lily bulb structure (Image source: Reference 3)

As an important energy storage organ, lily bulb accumulates substances mainly in the form of sucrose and starch. Starch and sucrose are the main forms of carbohydrates. They maintain the balance and coordination of various forms of carbohydrates and play a role in regulating the source-sink relationship of plants. The occurrence and development of lily bulb is closely related to carbohydrate metabolism.

Starch granules of different sizes in the outer scales of lily (Image source: Reference 2)

How are bulbs formed?

The process of bulb formation is called bulbization, which is the specialized development in the process of establishing the morphology of bulbous plants and is the result of the expression of specific plant genes.

Its formation mechanism can be considered to be that the external environmental conditions such as light and temperature induce changes in the physiological state of the body, activate bulb formation genes, express corresponding specific proteins, catalyze specific reactions, achieve a new balance of endogenous hormones, and cause changes in the pathways or rates of physiological metabolism in the body such as sugar metabolism and nitrogen metabolism. Finally, it is manifested in morphology as accelerated cell expansion growth, gradual cessation of elongation growth, and the beginning of bulb formation.

In addition, scientists pointed out that the length of the photoperiod plays a decisive role in the formation of bulbs. Regardless of onion or garlic type, longer days are conducive to the formation and expansion of bulbs. In the process of bulb formation, temperature and photoperiod have a mutually reinforcing effect. Under long days, when the temperature is high, the number of days required for bulb formation is less; when the temperature is low, the number of days required for bulb formation is more. Finally, the formation of bulbs may also be related to changes in endogenous hormones.

Difference Between Bulb and Corm

A modified underground stem that is easily confused with a bulb - the corm - is also relatively common. It is an underground modified stem with shortened internodes that swell into a spherical shape, often with a prominent terminal bud.

For example, the corm of water chestnut develops from the top of the slender creeper, with a thick terminal bud at the top of the corm, distinct nodes and internodes, and dry membranous scale leaves and axillary buds on the nodes. The corm stores a lot of nutrients and can be used for vegetative propagation.

Water chestnut bulb (Photo source: Veer Gallery)

You may complain that many corms and bulbs are difficult to distinguish because they look similar, but they are actually very easy to distinguish:

(1) The bulb stem is wrapped in layers of fleshy leaves , but the bulb is solid when cut open from the side;

(2) The bulb stem is shortened to a bulb disk , and the underground stem of the bulb is transformed into a spherical or oblate shape ;

(3) There is a well-developed terminal bud at the top of the corm, but there is no obvious terminal bud on the bulb.

Common bulb plants

Here we need to share some scientific knowledge. The so-called "bulb flowers" in the market are a general term for perennial herbaceous flowers including bulbs, corms, rhizomes, tubers, and tubers. Most bulb flowers are perennial herbaceous flowers with swollen parts formed by the metamorphosis of underground stems or roots. Bulb flowers are widely distributed all over the world, with hundreds of species in total.

Bulbous flowers, represented by tulips, bloom all over the world and are loved by people for their elegant and noble posture and rich colors. Bulbous flowers similar to tulips include hyacinths, daffodils, grape hyacinths, etc., all of which are bulbs.

Tulips, daffodils, and grape hyacinths (Image source: provided by the author)

In addition, lily is also an important bulb flower. It is a plant of the genus Lilium in the family Liliaceae. It is a plant that can be used as both medicine and food, and has ornamental value. The flowers contain aromatic oil and can be used as spices; the bulbs are rich in starch and are a precious food and also used as medicine.

Lily flowers (Photo credit: provided by the author)

Dried lily bulbs (Image source: Veer Gallery)

Common bulb plants

Saffron, as you may have heard of it, is a precious Chinese medicinal material. Saffron, also known as saffron and western saffron, is a perennial herb of the genus Crocus in the family Iridaceae. Only the pistil of the whole plant can be used. Each flower has 3 pistils, and about 200 flowers can be harvested to obtain 1 gram of pistil. In fact, the flowers of saffron are also very beautiful. They bloom in early spring and can be used as ornamental plants.

Crocus flowers (Image source: provided by the author)

The pistil of crocus (Image source: Veer Gallery)

There is also the water chestnut mentioned above, which is also a familiar bulb plant. It can usually be bought in the vegetable market or fruit stall. Raw water chestnuts are crisp, sweet and juicy, so they are also known as "underground snow pears".

Water chestnuts can be eaten directly as fruits, or as vegetables and cooked with other ingredients in soups, porridge or other delicious dishes. They can also be processed into preserved fruits, candied fruits, canned foods, beverages, yogurt and other products. Water chestnuts are rich in nutritional value and contain protein, fat, crude fiber and other functional active ingredients.

Water chestnut soup (Photo source: Veer Gallery)

Processed water chestnuts (Photo source: Veer Gallery)

Finally, I would like to introduce a plant called kohlrabi (piě), also known as bāi lán and bulgur. It is a biennial herb in the cruciferous family. Its bulbs have edible value and can be eaten fresh, cooked or pickled.

I remember when I was a kid, kohlrabi was planted in the yard almost every year. When it was ripe, I could often eat a cold dish of kohlrabi. The crispy taste and the aroma of chili were very impressive. Every autumn, the adults would pickle kohlrabi for the whole family to eat in winter when there were fewer vegetables.

Kohlrabi (Photo source: China Plant Image Library)

Kohlrabi salad (Photo source: Veer Gallery)

When you see plants that look like garlic, do you know what part they are?

Editor: Sun Chenyu

References:

1. Qiang Sheng. 2010. Botany. Higher Education Press;

2. Wu Shasha, Lü Yingmin, Zhang Qixiang. 2010. Changes in the ultrastructure of lily scales during bulb development. Acta Horticulturae Sinica 2010, 37(2): 247-255;

3. Lv Yingmin, Wu Shasha, Zhang Qixiang. 2009. Research progress in lily bulb developmental biology. Journal of Beijing Forestry University, 2009, 31 (5): 145-149;

4. Zhang Xuemin, Li Jiamin et al. 2022. Research progress on lily bulb development. Molecular Plant Breeding, first published online on July 28, 2022: https://kns.cnki.net/kcms/detail/46.1068.S.20220728.1205.008.html;

5. Xu Junxu, Li Qingzhu, et al. 2021. Research progress on the mechanism and regulation of bulb development in Lycoris. Acta Agronomica Sinica, 2021, 37(17): 39-44.