| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Amborellaceae Pichon.

Habit and leaf form. ‘Arborescent’, or shrubs; without essential oils (or nearly so). Leaves persistent; alternate; spiral to distichous; simple. Lamina dissected to entire; when dissected, pinnatifid (lobed); pinnately veined. Leaves exstipulate.

Leaf anatomy. Stomata present; anomocytic, or paracytic. The mesophyll without etherial oil cells.

Axial (stem, wood) anatomy. Nodes unilacunar (with one broad trace). Internal phloem absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays narrow. The axial xylem without vessels.

The axial xylem presumably with tracheids. ‘Included’ phloem absent.

Reproductive type, pollination. Fertile flowers functionally male, or functionally female. Unisexual flowers present. Plants dioecious.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. The ultimate inflorescence units cymose. Inflorescences axillary. Flowers partially acyclic. The perianth acyclic. Floral receptacle markedly hollowed (more or less, in female flowers), or not markedly hollowed (slightly convex, in male flowers). Free hypanthium present.

Perianth sequentially intergrading from sepals to petals; 5–8; weakly joined (basally); spiralled.

Androecium in male flowers 30–100 (‘more or less numerous’). Androecial members maturing centripetally (?); of the outer cycle adnate (basally, to the tepals); free of one another; 3–5 whorled (‘in several cycles’). Androecium (male flowers) exclusively of fertile stamens. Stamens 30–100 (‘more or less numerous’); more or less laminar. Anthers adnate (with adaxial thecae); non-versatile; dehiscing via longitudinal slits; introrse. Pollen grains aperturate to nonaperturate; if detectably aperturate, obscurely 1 aperturate (or with an irregular, distal, unthickened zone in the exine); sulcate.

Gynoecium 5–8 carpelled; apocarpous; eu-apocarpous (the carpels in a single whorl); superior. Carpel incompletely closed (unsealed at the tip); with a sessile stigma having two expanded flanges; 1 ovuled. Placentation marginal. Ovary stipitate. Ovules anatropous.

Fruit an aggregate. The fruiting carpel indehiscent; drupaceous (stipitate). Seeds endospermic. Embryo well differentiated (minute, basal). Cotyledons 2.

Physiology, phytochemistry. Aluminium accumulation demonstrated. Sieve-tube plastids S-type.

Geography, cytology. Paleotropical. New Caledonia. N = 13 (2n = 26).

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Magnoliiflorae; Laurales. Cronquist’s Subclass Magnoliidae; Laurales. APG III peripheral angiosperms; Superorder Amborellanae. APG IV Order Amborellales.

Species 1. Genera 1; Amborella trichopoda the only species.

General remarks. The 1999 International Botanical Congress (St. Louis) candidate for ‘the most primitive Angiosperm’!.

Illustrations. • Amborella trichopoda: Pflanzenreich IV, 1911.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 8th June 2026. delta-intkey.com’.

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