Succulent plant

      Not to be confused with cactus; botanically cacti are succulents but not all succulents are cacti.
      Succulent plants, such as this Aloe, store water in their fleshy leaves

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

      Definition

      There are a number of somewhat different definitions of the term succulent. One difference lies in whether or not roots are included in the parts of a plant which make it a succulent. Some authors include roots, as in the definition "plants in which the leaves, stem or roots have become more than usually fleshy by the development of water-storing tissue."[1] Others exclude roots, as in the definition "a plant with thick, fleshy and swollen stems and/or leaves, adapted to dry environments".[2] This difference affects the relationship between succulents and "geophytes" – plants that survive unfavourable seasons as a resting bud on an underground organ.[3] 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 are termed xerophytes; thus succulents are often 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.[4] Nor are all succulents xerophytes, since plants like Crassula helmsii are both succulent and aquatic.[5]

      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,[6] and "cacti and succulents" is the title or part of the title of many books covering the cultivation of these plants.[7][8][9] However, in botanical terminology, cacti are succulents.[1] Horticulturalists may also exclude other groups of plants, e.g. bromeliads.[10] A practical, but unscientific, horticultural definition is "a succulent plant is any desert plant that a succulent plant collector wishes to grow".[11] Such plants less often include geophytes (in which the swollen storage organ is wholly underground) but do include plants with a caudex,[12] which is a swollen above-ground organ at soil level, formed from a stem, a root or both.[3]

      A further difficulty is that plants are not either succulent or non-succulent. In many genera and families there is a continuous sequence 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 plant differently.[13]

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      Appearance

      A collection of succulent plants, including cacti

      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)[14]
      • very impervious outer cuticle (skin)[14]
      • mucilaginous substances, which retain water abundantly[14]
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      Habitat

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      Many succulents come from the dry areas of the tropics and subtropics, such as steppes, semi-desert, and desert. High temperatures and low precipitation force plants to collect and store water to survive long dry periods. Succulents may occasionally occur as epiphytes - "air plants" - as they have 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.

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      Evolution

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      The best-known succulents are cacti (family: Cactaceae). Virtually all cacti are succulents, but not all succulents are cacti. A unique feature of cacti is the possession of areoles, structures from which spines and flowers are produced.

      To differentiate between these two basic types that seem so similar, but that are unrelated succulent plants, use of the terms, cactus or cacti, only should be used to describe succulents in the cactus family. Popular collection of these types of plants has led to many Old World plants becoming established in the wild in the New World, and vice versa.

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      Families and genera

      		 This section includes a list of references, related reading or external links, but the sources of this section remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations. (September 2012)
      Apocynaceae: Pachypodium lealii, stem succulent
      Xanthorrhoeaceae: Haworthia arachnoidea, 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

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

      Order Alismatales

      Order Apiales

      Order Asparagales

      (succulent geophytes) Eulophia, Liparis, Oeceoclades
      (geophytes) Acroliphia, Bartholina, Bonatea, Brachycorythis, Brownleea, Centrostigma, Ceratandra, Corycium, Cynorkis, Didymoplexis, Disa, Disperis, Dracomonticola, Eulophia, Evotella, Gastrodia, Habernaria, Holothrix, Huttonaea, Neobolusia, Nervilia, Plicosepalus, Pachites, Platycoryne

      Order Asterales

      Order Brassicales

      Order Caryophyllales

      Order Commelinales

      Order Cornales

      Order Cucurbitales

      Order Diascoreales

      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 subfamily Succulent # Modified parts Distribution
      Agavoideae 300 Leaf North and Central America
      Cactaceae 1600 Stem (root, leaf) The Americas
      Crassulaceae 1300 Leaf (root) Worldwide
      Aizoaceae 2000 Leaf Southern Africa, Australia
      Apocynaceae 500 Stem Africa, Arabia, India, Australia
      Didiereaceae 11 Stem Madagascar (endemic)
      Euphorbiaceae > 1000 Stem and/or leaf and/or root Australia, Africa, Madagascar, Asia, the Americas, Europe
      Xanthorrhoeaceae 500+ Leaf Africa, Madagascar, Australia
      Portulacaceae  ? Leaf and stem The Americas, Australia, Africa
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      See also

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      References

      1. ^ a b Rowley 1980, p. 1
      2. ^ Beentje 2010, p. 116
      3. ^ a b Beentje 2010, p. 32
      4. ^ "xerophyte", Dictionary of Botany, 2001 onwards, retrieved 2012-09-23 
      5. ^ "Crassula helmsii (aquatic plant, succulent)", Global Invasive Species Database, ISSG, April 15, 2010, retrieved 2012-09-23 
      6. ^ Jacobsen 1960
      7. ^ Anderson 1999
      8. ^ Hecht 1994
      9. ^ Hewitt 1993
      10. ^ Innes & Wall 1995
      11. ^ Martin & Chapman 1977
      12. ^ Martin & Chapman 1977, pp. 19-20
      13. ^ Rowley 1980, p. 2
      14. ^ a b c Compton n.d.
      15. ^ Plants of Southern Africa Retrieved on 2010-1-1
      16. ^ FloraBase - The Western Australian Flora Retrieved on 2010-1-1
      17. ^ Australian Plant Names Index Retrieved on 2010-1-1
      18. ^ PlantZAfrica Retrieved on 2010-1-1
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      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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      External links

      Wikimedia Commons has media related to: Succulents
      Look up succulent in Wiktionary, the free dictionary.
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      Last modified on 9 June 2013, at 07:46