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| regnum = ] | regnum = ]
| unranked_divisio = ]s | unranked_divisio = ]s
| ordo = ] | ordo = '''Amborellales'''
| ordo_authority = Melikyan, A.V. Bobrov, & Zaytzeva, 1999
| familia = ] | familia = '''Amborellaceae'''
| familia_authority = ], 1948
| genus = '''''Amborella''''' | genus = '''''Amborella'''''
| genus_authority = ] | genus_authority = ]
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}} }}


'''''Amborella trichopoda''''' is a rare understory ] or small ] found only on the island of ]. Its wood lacks the vessels characteristic of most flowering plants. It is of great interest to science because ] analyses consistently place it at or near the base of the ] lineage. That is, it represents a line of flowering plants that diverged very early on (about 130 million years ago) from all the other extant species of flowering plants. Comparing characteristics of this basal angiosperm, other flowering plants and fossils may help us figure out how flowers first appeared--what Darwin called the "abominable mystery". '''''Amborella''''' is a genus of rare understory ]s or small ]s ] to the island of ]. The genus consists of only a single species, '''''Amborella trichopoda''''', and is the only member of the family '''Amborellaceae'''. Wood of ''Amborella'' lacks the vessels characteristic of most flowering plants. It is of great interest to plant systematists because ] analyses consistently place it at or near the ] of the ] lineage. That is, it represents a line of flowering plants that diverged very early on (about 130 million years ago) from all the other extant species of flowering plants. Comparing characteristics of this basal angiosperm, other flowering plants and fossils may help us figure out how flowers first appeared--what Darwin called the "abominable mystery".


==Description== ==Description==
''Amborella trichopoda'' is a sprawling shrub or small tree up to eight meters high. It bears alternate or decussate, simple evergreen leaves without stipules. The ] are two ranked, with serrated or rippled margins, and about 8 to 10 cm long. ''Amborella'' is a sprawling ] or small ] up to eight meters high. It bears alternate or decussate, simple evergreen leaves without ]s. The ] are two ranked, with distinctly serrated or rippled margins, and about 8 to 10 cm long.


The species is ]: each flower produces both ]s and ]s, but only one sex develops fully and is fertile in the flowers of an individual plant. The creamy white, inconspicuous ]s are arranged in panicles of 2 to 30 flowers borne in the axils of foliage leaves. Each flower is subtended by bracts and has a perianth of ]s arranged in a spiral or possible whorled at the periphery, suggesting that, as with other basal angiosperms, there is a high degree of developmental plasticity. The bracts gradually transition into tepals, making it difficult to determine where a flower actually begins. The species is ]: each flower produces both ]s and ]s, but only one sex develops fully and is fertile in the flowers of an individual plant. The small, creamy white, inconspicuous ]s are arranged in terminal ]s of 2 to 30 flowers borne in the axils of foliage leaves. Each flower is subtended by bracts and has a perianth of ]s (undifferentiated sepals and petals) arranged in a spiral or possibly whorled at the periphery. These features suggest that, as with other basal angiosperms, there is a high degree of developmental plasticity. The bracts gradually transition into tepals, making it difficult to determine where a flower actually begins.


Carpellate flowers are approximately 3 to 4 mm in diameter, with 7 or 8 tepals. There are 1 to 3 (or rarely none) well differentiated staminodes and a spiral of 4 to 8 carpels. Carpels have green ovaries and lack a style. They contain a single ovule with the micropyle directed downwards. Carpellate flowers are approximately 3 to 4 mm in diameter, with 7 or 8 tepals. There are 1 to 3 (or rarely none) well differentiated staminodes and a spiral of 4 to 8 free carpels (apocarpous). Carpels have green ovaries and 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 progessively smaller toward the center. The innermost may be sterile. Filaments are represented by a short broad stalk. Anthers are triangular and consist of four pollen sacs, two on each side, with a small sterile central 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 progessively smaller toward the center. The innermost may be sterile. Filaments are represented by a short broad stalk. Anthers are triangular and consist of four pollen sacs, two on each side, with a small sterile central
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Typically, 1 to 3 carpels develop into fruit per flower. The ] 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 ]. The embryo is small and surrounded by copious endosperm. Typically, 1 to 3 carpels develop into fruit per flower. The ] 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 ]. The embryo is small and surrounded by copious endosperm.

==Phylogeny==
].]]
This plant is currently accepted by plant systematists as the most basal lineage in the ] ]. By 'most basal' scientists mean that the Amborellaceae diverged the earliest from all other lineages of flowering plants. Comparing the derived characteristics that all other angiosperms share with each other, but not with the Amborella Family, may give scientists clues to what features early flowering plants had and how these characteristics have evolved through time. One early twentieth century idea of "primitive", or less derived, angiosperms that was accepted until relatively recently was modeled on the '']'' blossom with numerous ] arranged in spirals on an elongated receptacle rather than the small numbers of parts in distinct whorls of more derived flowers. However, studies of a well-preserved fossil putative aquatic angiosperm, '']'', have raised questions about what characteristics are more ancestral.

In a study designed to clarify relationships between the well-sequenced and well-studied model plants such as '']'', and the basal angiosperms such as ''Amborella'', '']'' of the Nymphaeaceae, '']'', the ], and more derived angiosperms, the eudicots, scientists examined the chloroplast genomes and expressed sequence tags of these organisms, and other seed plants to create this ]. Note that in this image, the angiosperms are all of the plants not labeled "gymnosperms." This hypothesized relationship of the extant seed plants places ''Amborella'' as the ] to all other angiosperms, and shows the gymnosperms as a monophyletic group sister to the angiosperms, supporting the theory that ''Amborella'' branched off earliest from all other living angiosperms. The dashed line between ''Amborella'' and ''Nuphar'' is meant to indicate some uncertainty about the relationship between the Amborellaceae and the Nymphaeaceae, and whether or not they form a clade that is sister to the angiosperms, rather than ''Amborella'' alone being a monophyletic group sister to the angiosperms.


==Classification== ==Classification==
''Amborella'' is placed alone in the family ]. In the most recent ] system, ], the Amborellaceae is placed in the monotypic order ] at the base of the angiosperm ]. ''Amborella'' is placed alone in the family ]. The ] recognized this family, but left it unplaced at order rank due to uncertainty about its relationship to the family ]. In the most recent ] system, ], the Amborellaceae is placed in the monotypic order ] at the base of the angiosperm ].

===Older systems===
The ], of 1981, assigned the family
: to the order ]
:: in subclass ],
::: in class ] ]]
:::: of division ] .

The ] placed it
: in the order ], which was assigned
:: to superorder ],
::: in subclass Magnoliideae ,
:::: in class Magnoliopsida .

The ] placed it
: in the order Laurales, which was assigned
:: to superorder Magnolianae
::: in subclass Magnoliideae ,
:::: in class Magnoliopsida .


==Ecology== ==Ecology==
Line 50: Line 77:


==References== ==References==
* Albert, V.A., et al., Floral gene resources from basal angiosperms for comparative genomics research, 2005. BMC Plant Biology, http://bmc.ub.uni-potsdam.de/1471-2229-5-5/1471-2229-5-5.pdf.
*Bailey IW and Swamy BGL (1948) Amborella trichopoda Baill., a new morphological type of vesselless dicotyledon. ''Journal of the Arnold Arboretum'' 29:245–254. * Bailey IW and Swamy BGL (1948) Amborella trichopoda Baill., a new morphological type of vesselless dicotyledon. ''Journal of the Arnold Arboretum'' 29:245–254.
*Buzgo, M, PS Soltis, DE Soltis (2004) Floral Developmental Morphology of Amborella trichopoda (Amborellaceae) ''International Journal of Plant Sciences'' 165(6):925-947 DOI: 10.1086/424024
*Endress PK and Igersheim A (2000) The reproductive structures of the basal angiosperm Amborella trichopoda (Amborellaceae). ''International Journal of Plant Science'' 161(supplement):S237–S248. * Buzgo, M, PS Soltis, DE Soltis (2004) Floral Developmental Morphology of Amborella trichopoda (Amborellaceae) ''International Journal of Plant Sciences'' 165(6):925-947 DOI: 10.1086/424024
* Endress PK and Igersheim A (2000) The reproductive structures of the basal angiosperm Amborella trichopoda (Amborellaceae). ''International Journal of Plant Science'' 161(supplement):S237–S248.
* Simpson, M.G. ''Plant Systematics''. Elsevier Academic Press. 2006.


==External links== ==External links==
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*], ]), article with detailed photos of plants in cultivation] *], ]), article with detailed photos of plants in cultivation]
* *
*


] ]
] ]


]
⚫ ]
]
] ]
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] ]
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Revision as of 02:39, 18 August 2011

Amborella
Amborella buds
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
Order: Amborellales
Melikyan, A.V. Bobrov, & Zaytzeva, 1999
Family: Amborellaceae
Pichon, 1948
Genus: Amborella
Baill.
Species: A. trichopoda
Binomial name
Amborella trichopoda
Baill.

Amborella is a genus of rare understory shrubs or small trees endemic to the island of New Caledonia. The genus consists of only a single species, Amborella trichopoda, and is the only member of the family Amborellaceae. Wood of Amborella lacks the vessels characteristic of most flowering plants. It is of great interest to plant systematists because molecular phylogenetic analyses consistently place it at or near the base of the flowering plant lineage. That is, it represents a line of flowering plants that diverged very early on (about 130 million years ago) from all the other extant species of flowering plants. Comparing characteristics of this basal angiosperm, other flowering plants and fossils may help us figure out how flowers first appeared--what Darwin called the "abominable mystery".

Description

Amborella is a sprawling shrub or small tree up to eight meters high. It bears alternate or decussate, simple evergreen leaves without stipules. The leaves are two ranked, with distinctly serrated or rippled margins, and about 8 to 10 cm long.

The species is dioecious: each flower produces both stamens and carpels, but only one sex develops fully and is fertile in the flowers of an individual plant. The small, creamy white, inconspicuous flowers are arranged in terminal panicles of 2 to 30 flowers borne in the axils of foliage leaves. Each flower is subtended by bracts and has a perianth of tepals (undifferentiated sepals and petals) arranged in a spiral or possibly whorled at the periphery. These features suggest that, as with other basal angiosperms, there is a high degree of developmental plasticity. The bracts gradually transition into tepals, making it difficult to determine where a flower actually begins.

Carpellate flowers are approximately 3 to 4 mm in diameter, with 7 or 8 tepals. There are 1 to 3 (or rarely none) well differentiated staminodes and a spiral of 4 to 8 free carpels (apocarpous). Carpels have green ovaries and 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 progessively smaller toward the center. The innermost may be sterile. Filaments are represented by a short broad stalk. Anthers are triangular and consist of four pollen sacs, two on each side, with a small sterile central connective. Stamens have papillate secretory tips. A small pyramidal structure in the center of the flower may represent a vestigial gynoecium.

Typically, 1 to 3 carpels develop into fruit per flower. 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.

Phylogeny

Cladogram showing relationship between Amborella of the Amborellaceae and other seed plants.

This plant is currently accepted by plant systematists as the most basal lineage in the angiosperms clade. By 'most basal' scientists mean that the Amborellaceae diverged the earliest from all other lineages of flowering plants. Comparing the derived characteristics that all other angiosperms share with each other, but not with the Amborella Family, may give scientists clues to what features early flowering plants had and how these characteristics have evolved through time. One early twentieth century idea of "primitive", or less derived, angiosperms that was accepted until relatively recently was modeled on the Magnolia blossom with numerous parts arranged in spirals on an elongated receptacle rather than the small numbers of parts in distinct whorls of more derived flowers. However, studies of a well-preserved fossil putative aquatic angiosperm, Archaefructus, have raised questions about what characteristics are more ancestral.

In a study designed to clarify relationships between the well-sequenced and well-studied model plants such as Arabidopsis thaliana, and the basal angiosperms such as Amborella, Nuphar of the Nymphaeaceae, Illicium, the monocots, and more derived angiosperms, the eudicots, scientists examined the chloroplast genomes and expressed sequence tags of these organisms, and other seed plants to create this cladogram. Note that in this image, the angiosperms are all of the plants not labeled "gymnosperms." This hypothesized relationship of the extant seed plants places Amborella as the sister taxon to all other angiosperms, and shows the gymnosperms as a monophyletic group sister to the angiosperms, supporting the theory that Amborella branched off earliest from all other living angiosperms. The dashed line between Amborella and Nuphar is meant to indicate some uncertainty about the relationship between the Amborellaceae and the Nymphaeaceae, and whether or not they form a clade that is sister to the angiosperms, rather than Amborella alone being a monophyletic group sister to the angiosperms.

Classification

Amborella is placed alone in the family Amborellaceae. The APG II system recognized this family, but left it unplaced at order rank due to uncertainty about its relationship to the family Nymphaeaceae. In the most recent APG system, APG III, the Amborellaceae is placed in the monotypic order Amborellales at the base of the angiosperm cladogram.

Older systems

The Cronquist system, of 1981, assigned the family

to the order Laurales
in subclass Magnoliidae,
in class Magnoliopsida
of division Magnoliophyta .

The Thorne system (1992) placed it

in the order Magnoliales, which was assigned
to superorder Magnolianae,
in subclass Magnoliideae ,
in class Magnoliopsida .

The Dahlgren system placed it

in the order Laurales, which was assigned
to superorder Magnolianae
in subclass Magnoliideae ,
in class Magnoliopsida .

Ecology

This species is threatened in the wild by habitat destruction due to overgrazing, fire, mining (one of the most pervasive causes of ecosystem loss in New Caledonia), and urban expansion.

Gallery

  • Amborella trichopoda Plant Amborella trichopoda Plant
  • Amborella trichopoda Branch and leaves Amborella trichopoda Branch and leaves
  • Amborella trichopoda Branch and leaves Amborella trichopoda Branch and leaves
  • Amborella trichopoda Branch and leaves Amborella trichopoda Branch and leaves
  • Amborella trichopoda Leaf Amborella trichopoda Leaf
  • Amborella trichopoda Branch and leaves Amborella trichopoda Branch and leaves
  • Amborella trichopoda Flowers Amborella trichopoda Flowers
  • Amborella trichopoda Flowers Amborella trichopoda Flowers
  • Amborella trichopoda Flowers Amborella trichopoda Flowers
  • Amborella trichopoda Flowers Amborella trichopoda Flowers
  • Amborella trichopoda Flowers Amborella trichopoda Flowers
  • Amborella trichopoda Flowers and leaves Amborella trichopoda Flowers and leaves

References

  • Albert, V.A., et al., Floral gene resources from basal angiosperms for comparative genomics research, 2005. BMC Plant Biology, http://bmc.ub.uni-potsdam.de/1471-2229-5-5/1471-2229-5-5.pdf.
  • Bailey IW and Swamy BGL (1948) Amborella trichopoda Baill., a new morphological type of vesselless dicotyledon. Journal of the Arnold Arboretum 29:245–254.
  • Buzgo, M, PS Soltis, DE Soltis (2004) Floral Developmental Morphology of Amborella trichopoda (Amborellaceae) International Journal of Plant Sciences 165(6):925-947 DOI: 10.1086/424024
  • Endress PK and Igersheim A (2000) The reproductive structures of the basal angiosperm Amborella trichopoda (Amborellaceae). International Journal of Plant Science 161(supplement):S237–S248.
  • Simpson, M.G. Plant Systematics. Elsevier Academic Press. 2006.

External links

Categories: