Succulent plant

Succulent plants store water in their fleshy stems, or leaves, such as this Aloe

In botany, succulent plants, also known as succulents, are plants that have some parts that are more than normally thickened and fleshy, usually to retain water in arid climates or soil conditions. The word "succulent" comes from the Latin word sucus, meaning juice, or sap.[1] Succulent plants may store water in various structures, such as leaves and stems. Some definitions also include roots, thus geophytes that survive unfavorable periods by dying back to underground storage organs may be regarded as succulents. In horticultural use, the term "succulent" is sometimes used in a way which excludes plants that botanists would regard as succulents, such as cacti. Succulents are often grown as ornamental plants because of their striking and unusual appearance.

Many plant families have multiple succulents found within them (over 25 plant families).[2] In some families, such as Aizoaceae, Cactaceae, and Crassulaceae, most species are succulents. The habitats of these water preserving plants are often in areas with high temperatures and low rainfall. Succulents have the ability to thrive on limited water sources, such as mist and dew, which makes them equipped to survive in an ecosystem which contains scarce water sources.

Definition

Center of a succulent (Aloe polyphylla)

A general definition of succulents is that they are drought resistant plants in which the leaves, stem or roots have become more than usually fleshy by the development of water-storing tissue.[3] Other sources exclude roots as in the definition "a plant with thick, fleshy and swollen stems and/or leaves, adapted to dry environments."[4] This difference affects the relationship between succulents and "geophytes" – plants that survive unfavorable seasons as a resting bud on an underground organ.[5] These underground organs, such as bulbs, corms and tubers, are often fleshy with water-storing tissues. Thus if roots are included in the definition, many geophytes would be classed as succulents. Plants adapted to living in dry environments such as succulents are termed xerophytes. However, not all xerophytes are succulents, since there are other ways of adapting to a shortage of water, e.g., by developing small leaves which may roll up or having leathery rather than succulent leaves.[6] Nor are all succulents xerophytes, since plants like Crassula helmsii are both succulent and aquatic.[7]

Those who grow succulents as a hobby use the term in a different way to botanists. In horticultural use, the term succulent regularly excludes cacti. For example, Jacobsen's three volume Handbook of Succulent Plants does not cover cacti,[8] and "cacti and succulents" is the title or part of the title of many books covering the cultivation of these plants.[9][10][11] However, in botanical terminology, cacti are succulents.[3] Horticulturists may also exclude other groups of plants, e.g., bromeliads.[12] A practical, but unscientific, horticultural definition is "a succulent plant is any desert plant that a succulent plant collector wishes to grow."[13] Such plants less often include geophytes (in which the swollen storage organ is wholly underground) but do include plants with a caudex,[14] which is a swollen above-ground organ at soil level, formed from a stem, a root or both.[5]

A further difficulty is that plants are not either succulent or non-succulent. In many genera and families there is a continuous gradation from plants with thin leaves and normal stems to those with very clearly thickened and fleshy leaves or stems, so that deciding what is a succulent is often arbitrary. Different sources may classify the same species differently.[15]

Appearance

A collection of succulent plants, including cacti, from the Jardin botanique d'Èze, France

The storage of water often gives succulent plants a more swollen or fleshy appearance than other plants, a characteristic known as succulence. In addition to succulence, succulent plants variously have other water-saving features. These may include:

  • Crassulacean acid metabolism (CAM) to minimize water loss
  • absent, reduced, or cylindrical-to-spherical leaves
  • reduction in the number of stomata
  • stems as the main site of photosynthesis, rather than leaves
  • compact, reduced, cushion-like, columnar, or spherical growth form
  • ribs enabling rapid increases in plant volume and decreasing surface area exposed to the sun
  • waxy, hairy, or spiny outer surface to create a humid micro-habitat around the plant, which reduces air movement near the surface of the plant, and thereby reduces water loss and creates shade
  • roots very near the surface of the soil, so they are able to take up moisture from very small showers or even from heavy dew
  • ability to remain plump and full of water even with high internal temperatures (e.g., 52 °C or 126 °F)[16]
  • very impervious outer cuticle (skin)[16]
  • mucilaginous substances, which retain water abundantly[16]

Habitat

Many succulents come from dry areas such as steppes, semi-desert, and desert. High temperatures and low precipitation force plants to collect and store water to survive long dry periods. Some species of cactus can survive for months without rainfall.[17] Succulents may occasionally occur as epiphytes, growing on other plants with limited or no contact with the ground, and are dependent on their ability to store water and gain nutrients by other means; this niche is seen in Tillandsia. Succulents also occur as inhabitants of sea coasts and dry lakes, which are exposed to high levels of dissolved minerals that are deadly to many other plant species.

Families and genera

Apocynaceae: Pachypodium lealii, stem succulent
Asphodelaceae: Haworthia arachnoidea, leaf succulent
Asphodelaceae: Astroloba tenax, leaf succulent
Cactaceae: Rebutia muscula, stem succulent
Crassulaceae: Crassula ovata, stem and leaf succulent
Euphorbiaceae: Euphorbia obesa ssp. symmetrica, stem succulent
Cylindropuntia imbricata: stem, woody succulent
Malvaceae: Adansonia digitata, stem succulent
Moringaceae: Moringa ovalifolia, stem succulent
Asparagaceae: Beaucarnea recurvata, stem succulent
Asparagaceae: Dracaena draco, stem succulent
Euphorbia resinifera
Succulents kept at 77 °F (25 °C) in a Connecticut greenhouse
Kalanchoe longiflora
Echeveria derenbergii

Plant orders, families, and genera in which succulent species occur are listed below.

Order Alismatales

Order Apiales

Order Asparagales

Order Asterales

Order Brassicales

Order Caryophyllales

Order Commelinales

Order Cornales

Order Cucurbitales

Order Dioscoreales

Order Ericales

Order Fabales

Order Gentianales

Order Geraniales

Order Lamiales

Order Malpighiales

Order Malvales

Order Myrtales

Order Oxalidales

Order Piperales

Order Poales

Order Ranunculales

Order Rosales

Order Santalales

Order Sapindales

Order Saxifragales

Order Solanales

Order Vitales

Order Zygophyllales

(unplaced order)* Boraginaceae: Heliotropium (unplaced order)* Icacinaceae: Pyrenacantha (geophyte)

For some families and subfamilies, most members are succulent; for example the Cactaceae, Agavoideae, Aizoaceae, and Crassulaceae.

The table below shows the number of succulent species found in some families:

Family or subfamilySucculent #Modified partsDistribution
Agavoideae300LeafNorth and Central America
Cactaceae1600Stem (root, leaf)The Americas
Crassulaceae1300Leaf (root)Worldwide
Aizoaceae2000LeafSouthern Africa, Australia
Apocynaceae500StemAfrica, Arabia, India, Australia
Asphodelaceae500+LeafAfrica, Madagascar, Australia
Didiereaceae11StemMadagascar (endemic)
Euphorbiaceae> 1000Stem or leaf or rootAustralia, Africa, Madagascar, Asia, the Americas, Europe
Portulacaceae~500Leaf and stemThe Americas, Australia, Africa
Edgerton Park Conservancy succulent at dusk.

Cultivation

Succulent "wall" in a nursery in San Francisco, United States consisting of Sempervivum, Echeveria and Crassula.

Succulents are favored as houseplants for their attractiveness and ease of care. If properly potted, succulents require little maintenance to survive indoors.[24] Succulents are very adaptable houseplants and will thrive in a range of indoor conditions.[25] For most plant owners over-watering and associated infections are main cause of death in succulents.

Succulents can be propagated by different means. The most common is vegetative propagation; this includes cuttings where several inches of stem with leaves are cut and after healing produce a callus. After a week or so, roots may grow. A second method is division consisting of uprooting an overgrown clump and pulling the stems and roots apart. The easiest one is allowing the formation of callus from a leaf. The vegetative propagation can be different according to the species.[26]

See also

References

  1. ↑ Merriam-Webster: succulent, retrieved 2015-04-13
  2. ↑ Dimmitt, Mark. "The Tucson Cactus and Succulent Society". www.tucsoncactus.org. Retrieved 5 February 2017.
  3. 1 2 Rowley 1980, p. 1
  4. ↑ Beentje 2010, p. 116
  5. 1 2 Beentje 2010, p. 32
  6. ↑ "xerophyte", Dictionary of Botany, 2001 onwards, retrieved 2012-09-23 Check date values in: |year= (help)
  7. ↑ "Crassula helmsii (aquatic plant, succulent)", Global Invasive Species Database, ISSG, April 15, 2010, retrieved 2012-09-23
  8. ↑ Jacobsen 1960
  9. ↑ Anderson 1999
  10. ↑ Hecht 1994
  11. ↑ Hewitt 1993
  12. ↑ Innes & Wall 1995
  13. ↑ Martin & Chapman 1977
  14. ↑ Martin & Chapman 1977, pp. 19-20
  15. ↑ Rowley 1980, p. 2
  16. 1 2 3 Compton n.d.
  17. ↑ kazilek (2 August 2014). "CAM Plants". askabiologist.asu.edu.
  18. ↑ "Apiaceae". succulent-plant.com. Retrieved 2018-02-07.
  19. ↑ Plants of Southern Africa Retrieved on 2010-1-1
  20. ↑ FloraBase - The Western Australian Flora Retrieved on 2010-1-1
  21. ↑ Parakeelya. The Plant List.
  22. ↑ Dregeochloa pumila. South African National Biodiversity Institute.
  23. ↑ "Crassulaceae Genera". Missouri Botanical Garden. Retrieved 2017-10-26.
  24. ↑ Kramer, Jack (1977). Cacti and Other Succulents. New York: Abrams. p. 9.
  25. ↑ Kramer, Jack (1977). Cacti and Other Succulents. New York: Abrams. p. 49.
  26. ↑ Lee, Debra (2007). Designing with Succulents. Portland, Obregon: Timber Press. p. 133.

Bibliography

  • Anderson, Miles (1999), Cacti and Succulents : Illustrated Encyclopedia, Oxford: Sebastian Kelly, ISBN 978-1-84081-253-4
  • Beentje, Henk (2010), The Kew Plant Glossary, Richmond, Surrey: Royal Botanic Gardens, Kew, ISBN 978-1-84246-422-9
  • Compton, R.H., ed. (n.d.), Our South African Flora, Cape Times Ltd, OCLC 222867742 (publication date also given as 1930s or 1940s)
  • Hecht, Hans (1994), Cacti & Succulents (p/b ed.), New York: Sterling, ISBN 978-0-8069-0549-5
  • Hewitt, Terry (1993), The Complete Book of Cacti & Succulents, London: Covent Garden Books, ISBN 978-1-85605-402-7
  • Innes, Clive & Wall, Bill (1995), Cacti, Succulents and Bromeliads, London: Cassell for the Royal Horticultural Society, ISBN 978-0-304-32076-9
  • Jacobsen, Hermann (1960), A Handbook of Succulent Plants (Vols 1–3), Poole, Dorset: Blandford Press, ISBN 978-0-7137-0140-1
  • Martin, Margaret J. & Chapman, Peter R. (1977), Succulents and their cultivation, London: Faber & Faber, ISBN 978-0-571-10221-1
  • Rowley, Gordon D. (1980), Name that Succulent, Cheltenham, Glos.: Stanley Thornes, ISBN 978-0-85950-447-8
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