Bulb
Overview
A bulb is a short stem with fleshy leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 or leaf bases. The leaves often function as food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...

 storage organ
Storage organ
A storage organ is a part of a plant specifically modified for storage of energy or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have an underground storage organ are called geophytes in the Raunkiær plant life-form...

s during dormancy
Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...

.

A bulb's leaf bases, known as scales, generally do not support leaves, but contain food reserves to enable the plant to survive adverse conditions. At the center of the bulb is a vegetative growing point or an unexpanded flowering shoot. The base is formed by a stem
Plant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...

, and plant growth occurs from this basal plate.
Encyclopedia
A bulb is a short stem with fleshy leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 or leaf bases. The leaves often function as food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...

 storage organ
Storage organ
A storage organ is a part of a plant specifically modified for storage of energy or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have an underground storage organ are called geophytes in the Raunkiær plant life-form...

s during dormancy
Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...

.

A bulb's leaf bases, known as scales, generally do not support leaves, but contain food reserves to enable the plant to survive adverse conditions. At the center of the bulb is a vegetative growing point or an unexpanded flowering shoot. The base is formed by a stem
Plant stem
A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence , conifer cones, roots, other stems etc. The internodes distance one node from another...

, and plant growth occurs from this basal plate. Root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

s emerge from the underside of the base, and new stems and leaves from the upper side. Tunicate bulbs have dry, membranous outer scales that protect the continuous lamina of fleshy scales. Species in the genera Allium
Allium
Allium is a monocot genus of flowering plants, informally referred to as the onion genus. The generic name Allium is the Latin word for garlic....

, Hippeastrum
Hippeastrum
Hippeastrum is a genus of about 90 species and 600+ hybrids and cultivars of bulbous plants in the family Amaryllidaceae, subfamily Amaryllidoideae, native to tropical and subtropical regions of the Americas from Argentina north to Mexico and the Caribbean. Some species are grown for their large...

, Narcissus, and Tulip
Tulip
The tulip is a perennial, bulbous plant with showy flowers in the genus Tulipa, which comprises 109 species and belongs to the family Liliaceae. The genus's native range extends from as far west as Southern Europe, North Africa, Anatolia, and Iran to the Northwest of China. The tulip's centre of...

a
all have tunicate bulbs. Non-tunicate bulbs, such as Lilium
Lilium
Lilium is a genus of herbaceous flowering plants growing from bulbs. Most species are native to the temperate northern hemisphere, though the range extends into the northern subtropics...

and Fritillaria species, lack the protective tunic and have looser scales.

Other types of storage organs (such as corm
Corm
A corm is a short, vertical, swollen underground plant stem that serves as a storage organ used by some plants to survive winter or other adverse conditions such as summer drought and heat ....

s, rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s, and tuber
Tuber
Tubers are various types of modified plant structures that are enlarged to store nutrients. They are used by plants to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction...

s) are sometimes erroneously referred to as bulbs. The technical term for plants that form underground storage organs, including bulbs as well as tubers and corms, is geophyte. Some epiphytic
Epiphyte
An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...

 orchids (family Orchidaceae
Orchidaceae
The Orchidaceae, commonly referred to as the orchid family, is a morphologically diverse and widespread family of monocots in the order Asparagales. Along with the Asteraceae, it is one of the two largest families of flowering plants, with between 21,950 and 26,049 currently accepted species,...

) form above-ground storage organs called pseudobulb
Pseudobulb
The pseudobulb is a storage organ derived from the part of a stem between two leaf nodes.It applies to the orchid family , specifically certain groups of epiphytic orchids, and may be single or composed of several internodes with evergreen or deciduous leaves along its length.In some species, it is...

s
, that superficially resemble bulbs.

Nearly all plants that form true bulbs are monocotyledon
Monocotyledon
Monocotyledons, also known as monocots, are one of two major groups of flowering plants that are traditionally recognized, the other being dicotyledons, or dicots. Monocot seedlings typically have one cotyledon , in contrast to the two cotyledons typical of dicots...

s, and include:
  • Onion
    Onion
    The onion , also known as the bulb onion, common onion and garden onion, is the most widely cultivated species of the genus Allium. The genus Allium also contains a number of other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion The onion...

    , garlic
    Garlic
    Allium sativum, commonly known as garlic, is a species in the onion genus, Allium. Its close relatives include the onion, shallot, leek, chive, and rakkyo. Dating back over 6,000 years, garlic is native to central Asia, and has long been a staple in the Mediterranean region, as well as a frequent...

    , and other allium
    Allium
    Allium is a monocot genus of flowering plants, informally referred to as the onion genus. The generic name Allium is the Latin word for garlic....

    s, family Alliaceae
    Alliaceae
    Allioideae is the botanical name of a monocot subfamily of flowering plants in the family Amaryllidaceae, order Asparagales. It was formerly treated as a separate family, Alliaceae...

    .
  • Lily, tulip
    Tulip
    The tulip is a perennial, bulbous plant with showy flowers in the genus Tulipa, which comprises 109 species and belongs to the family Liliaceae. The genus's native range extends from as far west as Southern Europe, North Africa, Anatolia, and Iran to the Northwest of China. The tulip's centre of...

    , and many other members of the lily family Liliaceae
    Liliaceae
    The Liliaceae, or the lily family, is a family of monocotyledons in the order Liliales. Plants in this family have linear leaves, mostly with parallel veins but with several having net venation , and flower arranged in threes. Several have bulbs, while others have rhizomes...

    .
  • Amaryllis
    Amaryllis
    Amaryllis is a small genus of flowering bulbs, with two species. The better known of the two, Amaryllis belladonna, is a native of South Africa, particularly the rocky southwest region near the Cape...

    , Hippeastrum
    Hippeastrum
    Hippeastrum is a genus of about 90 species and 600+ hybrids and cultivars of bulbous plants in the family Amaryllidaceae, subfamily Amaryllidoideae, native to tropical and subtropical regions of the Americas from Argentina north to Mexico and the Caribbean. Some species are grown for their large...

    , Narcissus, and several other members of the amaryllis family Amaryllidaceae
    Amaryllidaceae
    Amaryllidoideae is the subfamily of flowering plants that takes its name from the genus Amaryllis. It is part of the family Amaryllidaceae, in order Asparagales...

    .
  • Two groups of Iris
    Iris (plant)
    Iris is a genus of 260-300species of flowering plants with showy flowers. It takes its name from the Greek word for a rainbow, referring to the wide variety of flower colors found among the many species...

    species, family Iridaceae
    Iridaceae
    The Iris family or Iridaceae is a family of perennial, herbaceous and bulbous plants included in the monocot order Asparagales, taking its name from the genus Iris. Almost worldwide in distribution and one of the most important families in horticulture, it includes more than 2000 species...

    : subgenus Xiphium
    Iris xiphium
    Iris xiphium, commonly known as the Spanish Iris, is an iris native to Spain and Portugal.It is bulbous and bears handsome blue and yellow flowers, though they are not so large as those of I. xiphiodes. This species is also known as the Small Bulbous-rooted Iris. The Spanish Iris is favoured by...

    (the "Dutch" irises) and subgenus Hermodactyloides (the miniature "rock garden" irises).

Oxalis
Oxalis
Oxalis is by far the largest genus in the wood-sorrel family Oxalidaceae: of the approximately 900 known species in the Oxalidaceae, 800 belong here...

, in the family Oxalidaceae
Oxalidaceae
The Oxalidaceae, or wood sorrel family, are a small family of eight genera of herbaceous plants, shrubs and small trees, with the great majority of the 900 species in the genus Oxalis...

, is the only dicotyledon
Dicotyledon
The dicotyledons, also known as dicots, are a group of flowering plants whose seed typically has two embryonic leaves or cotyledons. There are around 199,350 species within this group...

 genus that produces true bulbs.

Bulbous plant species cycle through vegetative and reproductive growth stages; the bulb grows to flowering size during the vegetative stage and the plant flowers during the reproductive stage. Certain environmental conditions are needed to trigger the transition from one stage to the next, such as the shift from a cold winter to spring.

Bulbil

Some lilies form small bulbs, called bulbils in their leaf axils. Several members of the onion family, Alliaceae, including Allium sativum (garlic
Garlic
Allium sativum, commonly known as garlic, is a species in the onion genus, Allium. Its close relatives include the onion, shallot, leek, chive, and rakkyo. Dating back over 6,000 years, garlic is native to central Asia, and has long been a staple in the Mediterranean region, as well as a frequent...

), form bulbils in their flower heads, sometimes as the flowers fade, or even instead of the flowers. The so-called Tree onion
Tree onion
Tree onions, Allium ×proliferum, are similar to common onions, but with a cluster of bulblets where a normal onion would have flowers. Genomic evidence has conclusively shown that they are a hybrid of the common onion and the Welsh onion . However, some sources may still treat the tree onion as A....

 (Allium cepa var. proliferum) forms small onions which are large enough for pickling
Pickling
Pickling, also known as brining or corning is the process of preserving food by anaerobic fermentation in brine to produce lactic acid, or marinating and storing it in an acid solution, usually vinegar . The resulting food is called a pickle. This procedure gives the food a salty or sour taste...

.

Some ferns, such as Hen and Chicken Fern
Asplenium bulbiferum
Mother spleenwort, Asplenium bulbiferum, is a fern species native to Australia and New Zealand. It is also called hen and chicken fern and, in the Māori language, pikopiko and mouku. Its fronds are eaten as a vegetable....

produce new plants at the tips of the fronds' pinnae, which are sometimes referred to as bulbils.
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