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''Amborella'' is a monotypic genus of rare understory shrubs or small trees endemic to the main island, Grande Terre, of New Caledonia.〔 The genus is the only member of the family Amborellaceae and contains a single species, ''Amborella trichopoda''.〔 ''Amborella'' is of great interest to plant systematists because molecular phylogenetic analyses consistently place it at or near the base of the flowering plant lineage.〔〔 ==Description== ''Amborella'' is a sprawling shrub or small tree up to 8 m 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.〔 ''Amborella'' has xylem tissue that differs from that of other flowering plants. Xylem is the tissue that conducts water upwards in a vascular plant. Two of the main components of xylem in flowering plants are tracheids and vessel elements. Tracheid cells are typically pointed at each end, and have "pits" – regions often surrounded by thickenings adding mechanical strength – through which cells make contact with one another and can exchange fluids. The cells of vessel elements have actual perforations, usually on the flattened ends of the cells, through which fluids can be exchanged directly. Vessel elements form well-defined series of cells along the length of the stem; tracheids are arranged less regularly.〔 The xylem of ''Amborella'' contains only tracheids; vessel elements are absent.〔 Xylem of this form has long been regarded as a "primitive" feature of flowering plants.〔 The species is dioecious. This means that each plant produces either "male flowers" (meaning that they have functional stamens) or "female flowers" (flowers with functional carpels), but not both.〔 At any one time, a dioecious plant produces only functionally staminate or functionally carpellate flowers. Staminate ("male") ''Amborella'' flowers do not have carpels, whereas the carpellate ("female") flowers have non-functional "staminodes", structures resembling stamens in which no pollen develops. Plants may change from one reproductive morphology to the other. In one study, seven cuttings from a staminate plant produced, as expected, staminate flowers at their first flowering, but three of the seven produced carpellate flowers at their second flowering.〔 The small, creamy white, inconspicuous flowers are arranged in terminal inflorescences of 2 to 30 flowers, borne in the axils of foliage leaves.〔 The inflorescences have been described as "determinate thyrses", with up to three orders of branching, each branch being terminated by a flower. Each flower is subtended by bracts. The bracts gradually transition into a perianth of undifferentiated tepals, making it difficult to determine where a flower actually begins. The tepals typically are arranged in a spiral, but sometimes are whorled at the periphery. Carpellate flowers are roughly 3 to 4 mm 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. 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.〔 These features suggest that, as with other basal angiosperms, there is a high degree of developmental plasticity.〔 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Amborella」の詳細全文を読む スポンサード リンク
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