Pachypodium
This article includes a improve this article by introducing more precise citations. (June 2008) ) |
Pachypodium is a
Genus characteristics
All Pachypodium are
The pachycaul trunk is a morphologically enlarged trunk that stores water so as to survive seasonal drought or intermittent periods of root desiccation in exposed, dry, and rocky conditions. Whereas there is great variation in the habit of the plant body, all Pachypodium exhibit pachycaul growth. Variation in habit can range from dwarf flattened plants to bottle shaped shrubs to dendroid-shaped trees.
The second general characteristic of Pachypodium is spinescence, or having spines. The spines come clustered in either pairs or triplets with these clusters often arranged in rings or whorls around the trunk. Spines emerge with leaves, and like leaves grow for a short period before stopping growth and hardening. Spines do not regenerate so weathering and abrasion can wear away all but the youngest spines from older specimens - leaving smooth trunks and branches.
To some extent, branches are a characteristic of the genus. Some caution is warranted in overgeneralizing this characteristic. Pachypodium namaquanum is often branchless. Pachypodium brevicaule has no clear branches, and indeed may have evolved an alternative to branching in the form of nodes from which leaves, spines, and inflorescences emerge. In general Pachypodium have few branches. Since the environmental stresses and factors that contribute to branching can vary widely even in small areas, individual plants of the same species exhibit wide variation in branching morphology.
Unlike many members of the Apocynaceae, including some members of the superficially similar Adenium, Pachypodium species do not exude a milky latex. Rather, the sap is always clear.
Morphology
The
Morphologically, Pachypodium can be highly flexible in organization. Branching, if present at all, can be from either the base of the plant or at the crown. Freeform branching is a morphological adaptation to factors of the immediate microenvironment which, by their diversity, account for the wide range of habits:
- flattened dwarf species less than 8 cm tall but reaching 40 cm in diameter
- bottle- or oval-shaped shrubs to 4 m tall
- both branching and unbranched cigar- and cactus-like trees to 5 m tall.
Despite microenvironmental variation, Pachypodium are always succulent and always exhibit pachycaul trunks. Pachypodium are usually spinescent, but individual variation in spinescence as well as weathering and abrasion can result in plants with few if any spines.
Adaptive features
Variation among Pachypodium species is significant but all Pachypodium are succulent plants inhabiting seasonally or chronically dry landscapes. The genus employs two morphological
Pachycaul trunks
Pachypodium trunks and branches are thickened with water-storing tissue. Plants must rely on the food and water stored in their thickened trunks during seasonal or intermittent drought when leaves have been shed and no water is available from the substrate. In addition to the lower surface-to-volume ratio which aides in water retention, the thickened trunks and branches can also possess photosynthetic surface tissue to allow nutrient synthesis even when leaves are not present.
Some species of pachypodium have developed geophytic pachycaul trunks, or trunks that are beneath the soil's surface. These geophytic trunks are caudexes, enlarged stems or trunks that store water. They should not be mistaken for roots, because the enlargement occurs above the point where the roots branch off the main axis of the trunk.
Spinescence
The various species of Pachypodium are more or less heavily spined. Species from more arid regions have evolved denser and longer spines. Fog condenses on their spines in the form of dew, which drips down to the ground and increases the amount of moisture that's available to their often shallow roots.
The concept of "
(1) The variation of geology and topology in dry climates is thought to have a greater effect upon plants than in areas with high rainfall. Xeric environments are thus more demanding of adaptive mechanisms to aid in the plant's survival than in places where rainfall is plentiful. The more the demanding, generally the more "mechanized" or "mechanisms" are needed to aid the plants' survival.
(2) The geological formations of locally xeric landscapes break up
(3) Taxa tend to develop specialized xeromorphoric structures at some architectural level in
These newly created species from within the xeromorphic landscape take on different characters as responses to the
The adaptive mechanism in a morphological form and an ecological response to habitats are typically manifested together at once for the genus Pachypodium.
Examining Pachypodium reveals characteristics of various organs that adapt to the microenvironment. These adaptations, variations on habit,
The hypothesis of micro-endemism, therefore, states that speciation occurs in small specific habitats as aided by adaptive mechanism occurring in geological, topographical, and climatic isolation. Geologically and topographically, plant populations in xeric climates are broken down into smaller groups. The microclimate responds to the given location transforming it into a habitat. Isolated, the duplicity of organization in Pachypodium form through geology and location significant variation where over evolutionary time a new species might develop, if not have developed. The development of new species is through, in part, the adaptive mechanisms of pachycaul and spinescence as well as strict and flexible structural organization at various levels of plant physiology.
Taxonomy
Number of species
There are now 25 known species, of which 20 come from
Affinities within the Apocynaceae
The family Apocynaceae before it included Asclepiadaceae had 3
. The first two genera (Pachypodium and Adenium) are generally assumed to have a close association with each other. Studies; however, of these two genera reveal that they are not as intimately close as once thought.However, a study of key characteristics of the taxon and a
Distribution and habitats
Distribution
Pachypodium are native to Madagascar and continental Southern Africa, including Angola, Eswatini, Mozambique, Namibia, South Africa and Zimbabwe.
Habitat
Pachypodium in both mainland
In continental southern Africa, the extreme temperatures range from −10 °C (14 °F) in some locations to as high as 45 °C (113 °F), whereas in Madagascar, the temperature ranges from −6 to 40 °C (21 to 104 °F).
A generalization about
The genus grows in areas where there are significant dry seasons that range from five to ten months. For example, they are common in the Madagascar dry deciduous forests with their long dry season and severe limestone ridden soils.
Pachypodium grows in various types of
Sand readily store water because it is taken up easily and there is less evaporation except for the top layer. Very deep sand; however, has the problem of seepage. Yet in moderation shallow and deep sand substrates have water available to Pachypodium. With shallow sand substrates, Pachypodium grow on sand dunes near the sea. Where water is in deep sandy substrate, Pachypodium grow on sand "over" laterite red soil. Laterite soil is a largely impermeable soil that traps water for the use of the flora that include Pachypodium.
Protection status
Internationally Pachypodium are protected under the CITES treaty. According to it, members of this genus cannot be collected from endemic, native locations within the landscape. They are not easily, readily imported and exported between nations either. The protection afforded by the CITES treaty responses to two issues:
- The esteem the genus has within Collector's and Nursery Trade. As highly esteemed plants, succulent enthusiast desire to collect more and more species and cultivars. In the case of Pachypodium, seed, seedlings, and even mature, nursery-grown specimen plants are fortunately available readily in Nursery Trade.
- Destruction of the genus's endemic habitats, e.g. through agriculture.
Extinction of identified species seems yet unlikely, as the collection of seed and the cultivation of the plant safeguard the genus.
History of the genus
The early history of the genus Pachypodium demonstrates the typical process of a taxon becoming a new genus. Initially debate occurred over if Pachypodium belonged to the genus Echites or if it constituted a separate genus. Pachypodium were first published as a unique genus, separate from Echites, by Leandley in 1830.
Then the debate centered on the nomenclature of species uniquely found in continental Southern Africa. That changed when, in 1882, Baker contributed the first species accepted into the genus from Madagascar. The degree of speciation then turned to Madagascar, where the count of species far exceeds those on the mainland.
In 1907, Costantin and Bois constructed the first monograph, of Pachypodium, in which they enumerated 17 species, where ten were from Madagascar and seven were from continental southern Africa.
Natural history
There is no fossil records of Pachypodium known. Yet certain conclusions can be drawn from the geology of the landscape in Madagascar as to the past natural history of Pachypodium.
Vernacular names
In southern Africa it is called the Kudu Lily.[2] In Madagascar, they are known as bontaka, vontaka and votaka which means "swelling".[3]
References
- ^ "World Checklist of Selected Plant Families". Retrieved May 18, 2014.
- ^ Kudu Lily
- ^ de La Beaujardière, Jean-Marie, ed. (2001). "Botanical scientific names: Pachypodium". Malagasy Dictionary and Malagasy Encyclopedia.
Bibliography
- Eggli, Urs. (1993) Glossary of botanical terms with special reference to Succulent Plants. with German Equivalents (British Cactus & Succulent Society: United Kingdom)
- Endress, Mary E.; Bruyns, Peter V. (2000). "A revised classification of the Apocynaceae s.l." (PDF). The Botanical Review. 66 (1): 1–56. S2CID 31739212.
- Endress, Mary: "The unification of Asclepiadaceae and Apocynaceae." Haseltonia: The Cactus and Succulent Society of America's Yearbook Vol. 8.
- Lavranos, John, J. (2004) "Pachypodium makayense: A New Species From Madagascar". Cactus and Succulent Journal: United States 76 (2) 85–88.
- Lüthy, Jonas M. "Another look at the pachypodiums of Madagascar." Bradleya: The British Cactus and Succulent Society Yearbook. (22/2004) ISBN 0-902099-74-4
- Mays, Harry. [European Union Honorary Representative] "The Huntington Botanical Gardens' 2005 offering of International Succulent Introductions for the European Union." [A Posting] (Woodsleigh, Moss Lane, St. Michaels on Wyre, Preston, PR3 0TY, UK: 2005)
- Rapanarivo, S.H.J.V., Lavranos, J.J., Leeuwenberg, A.J.M., and Röösli, W. Pachypodium (Apocynaceae): Taxonomy, habitats and cultivation "Taxonomic revision of the genus Pachypodium," S.H.J.V. Rapanarivo and J.J. Lavranos; "The habitats of Pachypodium species" S.H.J.V. Rapanarivo; "Cultivation" W. Röösli. (A.A. Balkema: Rotterdam, Brookfield, 1999) [Rapanarivo et al.]
- Rowley, Gordon, D. Cactus Handbook 5: Pachypodium and Adenium (British Cactus and Succulent Society, (1983) 1999)
- Rowley, Gordon. Didiereaceae: "Cacti of the Old World" (The British Cactus and Succulent Society [BSCS]: 1992)
- Rowley, G.D. "The Pachypodium rosulatum aggregate (Apocynaceae) - one species or several?" Bradleya: The British Cactus and Succulent Society Yearbook. (16/1998)
- Rapanarivo, S.H.J.V., Lavranos, J.J., Leeuwenberg, A.J.M., and Röösli, W. Pachypodium (Apocynaceae): Taxonomy, habitats and cultivation "Taxonomic revision of the genus Pachypodium," S.H.J.V. Rapanarivo and J.J. Lavranos; "The habitats of Pachypodium species" S.H.J.V. Rapanarivo; "Cultivation" W. Röösli. (A.A. Balkema: Rotterdam, Brookfield, 1999, p. 5) [The rest of the list is based on Rapanarivo et al.(1999)]
- Rapanarivo et al. (1999) p. 5.
Further reading
- Dylan O. Burge; Kaila Mugford; Amy P. Hastings; Anurag A. Agrawal (2013). "Phylogeny of the plant genus Pachypodium (Apocynaceae)". PMID 23646289.