Amborella
Amborella | |
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Male specimen | |
Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Angiosperms |
Order: | Amborellales Melikyan, A.V.Bobrov, & Zaytzeva[3] |
Family: | Amborellaceae Pichon[3] |
Genus: | Amborella Baill.[2]
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Species: | A. trichopoda
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Binomial name | |
Amborella trichopoda Baill.[1] |
Amborella is a
Description
Amborella is a sprawling
Amborella has xylem tissue that differs from that of most other flowering plants. The xylem of Amborella contains only tracheids; vessel elements are absent.[7] Xylem of this form has long been regarded as a primitive feature of flowering plants.[8]
The species is
The small, creamy white flowers are arranged in
Carpellate flowers are roughly 3 to 4 millimetres (1⁄8 to 3⁄16 in) in diameter, with 7 or 8 tepals. There are 1 to 3 (or rarely 0) well-differentiated staminodes and a spiral of 4 to 8 free (apocarpous) carpels. Carpels bear green ovaries; they lack a style. They contain a single ovule with the micropyle directed downwards. Staminate flowers are approximately 4 to 5 mm in diameter, with 6 to 15 tepals. These flowers bear 10 to 21 spirally arranged stamens, which become progressively smaller toward the center. The innermost may be sterile, amounting to staminodes. The stamens bear triangular anthers on short broad filaments. An anther consists of four pollen sacs, two on each side, with a small sterile central connective. The anthers have connective tips with small bumps and may be covered with secretions.[12] These features suggest that, as with other basal angiosperms, there is a high degree of developmental plasticity.[10]
Typically, 1 to 3 carpels per flower develop into fruit. The fruit is an ovoid red drupe (approximately 5 to 7 mm long and 5 mm wide) borne on a short (1 to 2 mm) stalk. The remains of the stigma can be seen at the tip of the fruit. The skin is papery, surrounding a thin fleshy layer containing a red juice. The inner pericarp is lignified and surrounds the single seed. The embryo is small and surrounded by copious endosperm.[13]
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Specimen in Berkeley, California
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Young leaves
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Buds and staminate (male) flowers
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Diagram of a female flower with 5 carpels and 2 staminodes
Taxonomy
History
The Cronquist system, of 1981, classified the family:[14][15]
- Order Laurales
- Subclass Magnoliidae
- Class Magnoliopsida [=dicotyledons]
- Division Magnoliophyta [=angiosperms]
- Class Magnoliopsida [=dicotyledons]
- Subclass Magnoliidae
The
- Order Magnoliales
- Superorder Magnolianae
- Subclass Magnoliideae [=dicotyledons]
- Class Magnoliopsida [=angiosperms]
- Subclass Magnoliideae [=dicotyledons]
- Superorder Magnolianae
The Dahlgren system classified it:[18]
- Order Laurales
- Superorder Magnolianae
- Subclass Magnoliideae [=dicotyledons],
- Class Magnoliopsida [=angiosperms].
- Subclass Magnoliideae [=dicotyledons],
- Superorder Magnolianae
Modern classification
Amborella is the only genus in the family Amborellaceae. The
Phylogeny
Currently plant
In systematics the term "basal" describes a lineage that diverges near the base of a phylogeny, and thus earlier than other lineages. Since Amborella is apparently basal among the flowering plants, the features of early flowering plants can be inferred by comparing derived traits shared by the main angiosperm lineage but not present in Amborella. These traits are presumed to have evolved after the divergence of the Amborella lineage.One early 20th century idea of "primitive" (i.e. ancestral) floral traits in angiosperms, accepted until relatively recently, is the Magnolia blossom model. This envisions flowers with numerous parts arranged in spirals on an elongated, cone-like receptacle rather than the small numbers of parts in distinct whorls of more derived flowers.
In a study designed to clarify relationships between well-studied model plants such as
extant seed plants
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This hypothesized relationship of the extant seed plants places Amborella as the
Because of its evolutionary position at the base of the flowering plant clade, there was support for sequencing the complete genome of Amborella trichopoda to serve as a reference for evolutionary studies. In 2010, the US National Science Foundation began a genome sequencing effort in Amborella, and the draft genome sequence was posted on the project website in December 2013.[21]
Genomic and evolutionary considerations
Amborella is of great interest to plant systematists because
Amborella, being an understory plant in the wild, is commonly in intimate contact with shade- and moisture-dependent organisms such as algae, lichens and mosses. In those circumstances, some horizontal gene transfer between Amborella and such associated species is not surprising in principle, but the scale of such transfer has caused considerable surprise. Sequencing the Amborella mitochondrial genome revealed that for every gene of its own origin, it contains about six versions from the genomes of an assortment of the plants and algae growing with or upon it. The evolutionary and physiological significance of this is not as yet clear, nor in particular is it clear whether the horizontal gene transfer has anything to do with the apparent stability and conservatism of the species.[28][29]
Ecology
Amborella is typically dioecious, but has been known to change sex in cultivation.[5] Amborella has a mixed pollination system, relying on both insect pollinators and wind.[9]
Conservation
The islands of New Caledonia are a biodiversity hot-spot, preserving many early diverging lineages of plants, of which Amborella is but one. This preservation has been ascribed to climate stability during and since the Tertiary (66 to 3 million years ago), stability that has permitted the continued survival of tropical forests on New Caledonia. In contrast, drought conditions dominated the Australian climate towards the end of the Tertiary. Current threats to biodiversity in New Caledonia include fires, mining, agriculture, invasion by introduced species, urbanization and global warming.[23] The importance of conserving Amborella has been dramatically stated by Pillon: "The disappearance of Amborella trichopoda would imply the disappearance of a genus, a family and an entire order, as well as the only witness to at least 140 million years of evolutionary history."[30] Conservation strategies targeted on relict species are recommended, both preserving a diversity of habitats in New Caledonia and ex situ conservation in cultivation.[23]
References
- ^ "Amborella trichopoda". International Plant Names Index (IPNI). Royal Botanic Gardens, Kew; Harvard University Herbaria & Libraries; Australian National Botanic Gardens. Retrieved 23 September 2023.
- ^ "Amborella". International Plant Names Index (IPNI). Royal Botanic Gardens, Kew; Harvard University Herbaria & Libraries; Australian National Botanic Gardens. Retrieved 23 September 2023.
- ^ hdl:10654/18083.
- ^ Jérémie, J. (1982). "Amborellacées". In A. Aubréville; J. F. Leroy (eds.). Flore de La Nouvelle-Calédonie et Dépendances (in French). Vol. 11. Paris: Muséum National d’Histoire Naturelle. pp. 157–160.
- ^ a b c d Große-Veldmann, B.; Korotkova, N.; Reinken, B.; Lobin, W. & Barthlott, W. (2011). "Amborella trichopoda — Cultivation of the most ancestral angiosperm in botanic gardens". The Journal of Botanic Garden Horticulture. 9: 143–155. Retrieved 2016-10-21.
- ^ a b Simpson, M.G. (2010). Plant Systematics (2nd ed.). Elsevier. p. 186
- S2CID 35832198.
- ISBN 978-0-09-120611-6. p. 98.
- ^ JSTOR 3298537.
- ^ S2CID 84793812.
- ^ doi:10.1139/b03-004
- S2CID 84820330.
- S2CID 2142920.
- ISBN 9780231038805.
- ^ Cronquist, A. (1988). The evolution and classification of flowering plants (2nd ed.). Bronx, NY: New York Botanical Garden.
- S2CID 40348158.
- S2CID 85738663.
- .
- ^
- ^ PMID 15799777.
- ^ "Amborella Genome Database". Archived from the original on 2020-01-29. Retrieved 2017-12-21.
- ^ ISBN 978-3-7091-1160-4.
- ^ a b c Pillon, Y. (2008). Biodiversité, origine et évolution des Cunoniaceae : implications pour la conservation de la flore de Nouvelle-Calédonie (PDF) (PhD) (in French and English). University of New Caledonia. Retrieved 2013-06-22.
- PMID 24391149.
- PMID 21628174
- ^ Water lily genome expands picture of the early evolution of flowering plants
- PMID 17041880.
- ^ Megan Scudellari. Genomes Gone Wild, January 1, 2014 |
- S2CID 2499045.
- ^ Pillon 2008, p. 55. "La disparition d’Amborella trichopoda impliquerait donc la disparition d’un genre, d’une famille et d’un ordre entier, ainsi que le seul témoin d’au moins 140 millions d’années d’histoire évolutive."
Further reading
- Bailey, I.W. & Swamy, B.G.L. (1948). "Amborella trichopoda Baill., a new morphological type of vesselless dicotyledon". Journal of the Arnold Arboretum. 29 (3): 245–254. S2CID 240346942.
- Endress, P.K.; Igersheim, A. (2000). "The reproductive structures of the basal angiosperm Amborella trichopoda (Amborellaceae)". International Journal of Plant Sciences. 161(supplement): S237–S248. S2CID 84820330.
- PMID 18341710.
- Zuccolo, A.; Bowers, J. E.; Estill, J. C.; Xiong, Z.; Luo, M.; Sebastian, A.; Goicoechea, J. L.; Collura, K.; Yu, Y.; Jiao, Y.; Duarte, J.; Tang, H.; Ayyampalayam, S.; Rounsley, S.; Kudrna, D.; Paterson, A. H.; Pires, J. C.; Chanderbali, A.; PMID 21619600.
External links
- The Amborella Genome Sequencing Project Archived 2020-01-29 at the Wayback Machine
- Amborellaceae Archived 2005-02-12 at the Wayback Machine in L. Watson and M.J. Dallwitz (1992 onwards). The families of flowering plants: descriptions, illustrations, identification, information retrieval. Archived 2007-01-03 at the Wayback Machine via Description language for taxonomy Archived 2007-01-03 at the Wayback Machine
- Ancient plant provides clues to evolutionary mystery (National Science Foundation)
- National Tropical Botanical Garden (Hawaii, United States), article with detailed photos of plants in cultivation
- Nova "First Flower" (transcript)
- NCBI Taxonomy Browser