In botany, a bulb is structurally a short

stem Stem or STEM may refer to: Plant structures * Plant stem, a plant's aboveground axis, made of vascular tissue, off which leaves and flowers hang * Stipe (botany), a stalk to support some other structure * Stipe (mycology), the stem of a mushro ...

with fleshy

leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

or leaf basesBell, A.D. 1997. ''Plant form: an illustrated guide to flowering plant morphology''. Oxford University Press, Oxford, U.K. that function as

food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is inge ...

storage organ A storage organ is a part of a plant specifically modified for storage of energy (generally in the form of carbohydrates) or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have ...

s during

dormancy Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be clo ...

. (In

gardening Gardening is the practice of growing and cultivating plants as part of horticulture. In gardens, ornamental plants are often grown for their flowers, foliage, or overall appearance; useful plants, such as root vegetables, leaf vegetables, fruits ...

, plants with other kinds of storage organ are also called " ornamental bulbous plants" or just "bulbs".)

Description

The bulb's leaf bases, also 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 reduced

, and plant growth occurs from this basal plate. Roots 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'', '' Hippeastrum'', ''

Narcissus Narcissus may refer to: Biology * ''Narcissus'' (plant), a genus containing daffodils and others People * Narcissus (mythology), Greek mythological character * Narcissus (wrestler) (2nd century), assassin of the Roman emperor Commodus * Tiberiu ...

'', and '' Tulipa'' all have tunicate bulbs. Non-tunicate bulbs, such as '' Lilium'' and '' Fritillaria'' species, lack the protective tunic and have looser scales. 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. Once the flowering period is over, the plant enters a foliage period of about six weeks during which time the plant absorbs nutrients from the soil and energy from the sun for setting flowers for the next year. Bulbs dug up before the foliage period is completed will not bloom the following year but then should flower normally in subsequent years.

Plants that form bulbs

Plants that form underground

s, including bulbs as well as tubers and corms, are called ''geophytes''. Some

epiphytic An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...

orchids (family Orchidaceae) form above-ground storage organs called '' pseudobulbs'', that superficially resemble bulbs. Nearly all plants that form true bulbs are monocotyledons, and include: * '' Amaryllis'', '' Crinum'', '' Hippeastrum'', ''

'', and several other members of the amaryllis family

Amaryllidaceae The Amaryllidaceae are a family of herbaceous, mainly perennial and bulbous (rarely rhizomatous) flowering plants in the monocot order Asparagales. The family takes its name from the genus ''Amaryllis'' and is commonly known as the amaryllis fa ...

. This includes onion,

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus ''Allium''. Its close relatives include the onion, shallot, leek, chive, Allium fistulosum, Welsh onion and Allium chinense, Chinese onion. It is native to South A ...

, and other alliums, members of the Amaryllid subfamily Allioideae. * Lily, tulip, and many other members of the lily family Liliaceae. * Two groups of '' Iris'' species, family Iridaceae: subgenus '' Xiphium'' (the "Dutch" irises) and subgenus ''

Hermodactyloides The subgenus ''Hermodactyloides'' of Iris includes all reticulate-bulbed bulbous irises. It was formerly named as a genus, ''Iridodictyum'' by Rodionenko in 1961. but it was not widely accepted and most botanists preferred 'Hermodactyloides'. ...

'' (the miniature "rock garden" irises). '' Oxalis'', in the family

Oxalidaceae The Oxalidaceae, or wood sorrel family, are a small family of five genera of herbaceous plants, shrubs and small trees, with the great majority of the 570 species in the genus ''Oxalis'' (wood sorrels). Members of this family typically have divid ...

, is the only

dicotyledon The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, t ...

genus that produces true bulbs.

Bulbil

A bulbil is a small bulb, and may also be called a bulblet, bulbet, or bulbel. Small bulbs can develop or propagate a large bulb. If one or several moderate-sized bulbs form to replace the original bulb, they are called renewal bulbs. Increase bulbs are small bulbs that develop either on each of the leaves inside a bulb, or else on the end of small underground stems connected to the original bulb. Some lilies, such as the tiger lily '' Lilium lancifolium'', form small bulbs, called bulbils, in their leaf

axil A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...

s. Several members of the onion family, Alliaceae, including ''Allium sativum'' (

), form bulbils in their flower heads, sometimes as the flowers fade, or even instead of the flowers (which is a form of

apomixis In botany, apomixis is asexual reproduction without fertilization. Its etymology is Greek for "away from" + "mixing". This definition notably does not mention meiosis. Thus "normal asexual reproduction" of plants, such as propagation from cuttin ...

). The so-called tree onion (''Allium'' × ''proliferum'') forms small onions which are large enough for pickling. Some ferns, such as the hen-and-chicken fern, produce new plants at the tips of the fronds' pinnae that are sometimes referred to as bulbils. Image:Lilium lancifolium bulbils.jpg, Bulbils form in the leaf axils of '' Lilium lancifolium'' Image:Alliumvineale1web.jpg, Wild garlic (''

Allium vineale ''Allium vineale'' (wild garlic, onion grass, crow garlic or stag's garlic) is a perennial, bulb-forming species of wild onion, native to Europe, northwestern Africa and the Middle East. The species was introduced in Australia and North America ...

'') bulbils sprouting Image:Allium fistulosum bulbifera0.jpg, " Tree onions" form clusters of small bulbs instead of flowers

Description

Plants that form bulbs

Bulbil

See also

References

Further reading