Aponogeton

Aponogeton
A. distachyos, foliage and
inflorescence at water surface
Scientific classification
Kingdom: Plantae
Clade: Angiosperms
Clade: Monocots
Order: Alismatales
Family: Aponogetonaceae
Planch.[1]
Genus: Aponogeton
L.f.
Species

See text

The Aponogetonaceae (Cape-pondweed family or Aponogeton family) are a family of flowering plants in the order Alismatales. The Aponogetonaceae is considered to be allied to the Potamogetonaceae - Najadaceae complex of families.

In recent decades the family has had universal recognition by taxonomists.[2] The APG system (1998) and APG II system (2003) treat it in the order Alismatales in the clade monocots. The family consists of only one genus, Aponogeton, with 56 known species (Christenhusz & Byng 2016 [3]) of aquatic plants, most of which have been included in a molecular phylogeny by Chen et al. (2015). The name was published in Supplementum Plantarum 32: 214 (1782) and is derived from a geographic location. Some species are used as ornamental plants in aquariums.

Distribution

They are aquatic plants, which are found in tropical to warm temperate regions of Africa, Asia and Australasia.[4]

Aponogeton distachyos is originally from South Africa but has become naturalised in South Australia, Western South America, and Western Europe.

Individual plants are not always easy to identify due to hybridization (particularly those sold as A. crispus - which are often cultivated hybrids with A. natans or A. rigidifolius).

Generally an Aponogeton from Asia will have a single bloom stalk, while those from African heritage (including Madagascar) will have multiple blooming stems on the same flower stalk.

Even though 17 species are found in Africa, only one of them, A. distachyos, has been continuously maintained as a plant in garden ponds. Several of the 11 Madagascan species have been introduced as new aquarium plants in the early 21st century. At present, the following plants from Madagascar are in culture: Aponogeton boivinianus, A. longiplumulosus, A. madagascariensis and A. ulvaceus. Additionally, Aponogeton bernierianus, A. capuronii, A. decaryi and A. tenuispicatus have been imported on several occasions but have not achieved any wider distribution because they are difficult to maintain. From the 16 representatives of this genus from Asia and Australia, A. crispus, A. elongatus, A. rigidifolius, A. robinsonii and A. undulatus are useful aquarium plants. Aponogeton jacobensii, A. natans and A. loriae, too, were cultivated several times but have not proven themselves under aquarium conditions.

Ecology

A. distachyos, habit, showing aerial and submerged parts

Many species grow in temporarily still or flowing waters and live through the dry period as a dormant tuber. They are fully aquatic herbaceous plants with milky sap, becoming dormant during drought conditions. Most species grow from tubers. Most Asian species remain submerged all year round, while the starchy tubercles of the African species are able to survive the dry season by shedding their leaves and undergoing a dormant period.

Almost all Aponogeton species go through resting and growth phases in their natural locations, triggered by the local ecological conditions. During growth periods the plant will deposit proteins, fats, carbohydrates and mineral substances in the storage rhizome or tuber During the resting period the tuber survives in the soil in order to again sprout during the following vegetation period. Tubers in Aponogeton species have a high resistance to drying out. This ability to store water is exploited, for instance, in the annual export of thousands of dormant A. crispus specimens, shipped in large bags in a totally dry state. Special care has to be taken, however, to prevent the tubers from contracting. At the same time, the vegetative point must not be damaged.

According to Christel Kasselman,[5] in previous aquarium literature the assertion, which is wrong in this form, has been disseminated, stating that all cultivated Aponogeton species are subjected to a periodical drying out of waterways in their natural habitats. It is subsequently being suggested that at the onset of the resting period — indicated by the plant through ending leaf production — the tuber should be removed from the aquarium and be stored in a cool and more or less moist state for several months. According to Kasselmann's experience, obtained at numerous locations, these assertions and conclusions will often lead to maintenance not appropriate to biotope conditions, with the result that plants eventually die off. These erroneous ideas, widespread among the aquarium community, can quite possibly be traced back to the first mass import of A. crispus in the early 1950s, since the above assertions do in fact mostly apply to this species. They were erroneously applied to other species imported later. In order to achieve maintenance in accordance with biotope-specific requirements, the ecological conditions in which Aponogeton species prosper have to be viewed in a more differentiating manner than has previously been the case. Therefore, a description of specific features of different types of waters accommodating Aponogeton varieties is provided at this point. In the sections on the individual species the known ecological conditions are listed, enabling the reader a classification into different categories. Data on cultivation will help to contribute to a successful, species-specific maintenance. It should be noted, though, that because of a lack of ecological data it is difficult to classify some species into the system.

Basically one can distinguish between four different categories of types of waters accommodating Aponogeton species. It has to be noted that some species can be found in more than one type of waterway.

Economic uses

The tubers of several species are eaten by humans and their livestock. Some are grown as ornamental plants in aquariums or ponds.

Cultivation

An African Aponogeton with a triple flower spike.

All Aponogeton species are easy to grow when their preferences are met. The Madagascar lace plants (A. madagascarensis) require special handling as they prefer cooler water – 70 °F (21 °C) as a maximum. As of 2010, the Australian species exist in very small numbers in the hobby.

Rest periods

The African species in particular (with the exception of A. rigidifolius that has a rhizome and not a tuber) experience a natural rest period, corresponding to their habitat drying out in the wild. The Asian species may also have a rest period, but this is temperature related. As the plant stops growing it can be taken out of the pond or aquarium and put in a bowl of damp sand. Keep the bowl in a dark, cool place with the sand kept damp for approximately 2–3 months at a temperature of about 50–64 °F (10–18 °C) until small leaves are seen to sprout from the tuber when they can be returned to the pond or aquarium.[6]

Selected species

Sources:[2][7][8]

References

  1. ↑ Angiosperm Phylogeny Group (2009), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III", Botanical Journal of the Linnean Society, 161 (2): 105–121, doi:10.1111/j.1095-8339.2009.00996.x, retrieved 2010-12-10
  2. 1 2 van Bruggen, H. W. E. (1985). "Monograph of the genus Aponogeton (Aponogetonaceae)". Bibliotheca botanica. Stuttgart: E. Schweizerbart'sche Verlagsbuchhandlung. 33 (137): i–viii, 1–76. ISBN 978-3-510-48008-1. ISSN 0067-7892. Retrieved 2010-03-13.
  3. ↑ Christenhusz, M. J. M. & Byng, J. W. (2016). "The number of known plants species in the world and its annual increase". Phytotaxa. Magnolia Press. 261 (3): 201–217. doi:10.11646/phytotaxa.261.3.1.
  4. ↑ Watson, L. & Dallwitz, M. J. (1992 onwards): Aponogetonaceae Archived April 24, 2006, at the Wayback Machine.
  5. ↑ Kasselmann, Aquarium Plants 2003, s.v. "The Aponogeton genus"
  6. ↑ Gesting, B. Nature and Aquarium
  7. ↑ African Flowering Plants Database: Aponogeton
  8. ↑ Huxley, A., ed. (1992). New RHS Dictionary of Gardening. Macmillan ISBN 0-333-47494-5.
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