Fruit structure of Amborella trichopoda (Amborellaceae)

The indehiscent fruitlets of the apparently basalmost extant angiosperm,Amborella trichopoda, have a pericarp that is differentiated into five zones, a thin one-cell-layered skin (exocarp), a thick fleshy zone of 25-35 cell layers (outer mesocarp), a thick, large-celled sclerenchymatous zone (unlignified) of 6-18 cell layers (middle mesocarp), a single cell layer with thin-walled (silicified?) cells (inner mesocarp), and a 2-4-cell-layered, small-celled sclerenchymatous zone (unlignified) derived from the inner epidermis (endocarp). The border between inner and outer mesocarp is not even but the inner mesocarp forms a network of ridges and pits; the ridges support the vascular bundles, which are situated in the outer mesocarp. In accordance with previous observations by Bailey & Swamy, no ethereal oil cells were observed in the pericarp; however, lysigenous cavities as mentioned by these authors are also lacking; they seem to be an artefact caused by re-expanding dried fruits. The seed coat is not sclerified. The fruitlets of Amborella differ from externally similar fruits or fruitlets in other basal angiosperms, such as Austrobaileyales or Laurales, in their histology. (c) 2005 The Linnean Society of London.