The families of flowering plants

L. Watson and M.J. Dallwitz

Aucubaceae J.G. Agardh

~ Cornaceae sensu lato, Garryaceae.

Habit and leaf form. Small herbs, or shrubs. Leaves persistent; opposite; flat; leathery; petiolate; somewhat connate; simple. Lamina entire; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins entire, or dentate. Vegetative buds scaly. Leaf development not ‘graminaceous’.

General anatomy. Plants with ‘crystal sand’ (in leaf and axis).

Leaf anatomy. The leaf lamina dorsiventral (with 1–3 layers of palisade). Stomata present; mainly confined to one surface (the lower); anomocytic. Hairs present, or absent (?); if present, eglandular. Lamina without secretory cavities. Minor leaf veins without phloem transfer cells.

Axial (stem, wood) anatomy. Secretory cavities absent. Nodes tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays narrow.

The wood semi-ring porous to diffuse porous. The vessel end-walls scalariform. The axial xylem with fibre tracheids; with libriform fibres; without septate fibres. The fibres with spiral thickening. The parenchyma paratracheal (as occasional cells touching the vessels). ‘Included’ phloem absent.

Reproductive type, pollination. Plants dioecious.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. The ultimate inflorescence units cymose. Inflorescences terminal, or axillary; dichotomous thyrses. Flowers bracteolate (female), or ebracteolate (male); small; regular; 4 merous; cyclic.

Perianth with distinct calyx and corolla (but the sepals minute); 8; 2 whorled; isomerous. Calyx 4; 1 whorled; polysepalous; regular; persistent. Corolla 4; 1 whorled; polypetalous; valvate; regular; with contrasting markings. Petals sessile.

Androecium (male flowers) 4. Androecial members free of the perianth; all equal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 4; isomerous with the perianth; oppositisepalous; alternating with the corolla members; filantherous (very short). Anthers dorsifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate. Pollen grains aperturate; 3 aperturate; colporate; 2-celled.

Gynoecium 1 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium monomerous (ostensibly), or syncarpous (i.e. supposedly ‘pseudomonomeric’); of one carpel, or eu-syncarpous (according to interpretation); inferior. Carpel (if considered monomeric) stylate; apically stigmatic; 1 ovuled. Placentation apical. Ovary (if considered ‘pseudomonomeric’) 1 locular. Epigynous disk present (fleshy). Gynoecium stylate. Styles 1; apical. Stigmas 1; capitate (conspicuous, oblique). Placentation apical. Ovules pendulous; apotropous; with dorsal raphe; anatropous; unitegmic; crassinucellate. Endothelium differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Endosperm formation cellular.

Fruit fleshy. The fruiting carpel (if considered monomeric) baccate (scarlet). Fruit (if considered syncarpous) indehiscent; a berry; 1 seeded. Seeds copiously endospermic. Embryo small.

Physiology, phytochemistry. Not cyanogenic. Verbascosides not detected. Iridoids detected; ‘Route II’ type (+decarb.). Proanthocyanidins absent. Flavonols present; kaempferol and quercetin. Ellagic acid absent.

Geography, cytology. Holarctic. Himalayas to Japan.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli (?). Dahlgren’s Superorder Corniflorae; Cornales. Cronquist’s Subclass Magnoliidae; Laurales. APG III core angiosperms; core eudicot; Superorder Asteranae; lamiid. APG IV Order Garryales (as a synonym of Garryaceae).

Species 3. Genera 1; only genus, Aucuba.

General remarks. Exemplifying the well known difficulties in distributing certain Dicot families between Dahlgren’s Araliiflorae and Corniflorae. It is equally hard to assign them with confidence to the higher level groupings Crassinucelli and Tenuinucelli, although the latter evidently represent a major divergence in the Dicot line of descent (cf.Young and Watson 1970, Chase et al. 1993). In terms of this description, Aucuba exhibits numerous differences from Garryaceae, involving inflorescence and floral morphology (perianth, androecium, gynoecium); and data relying on limited sampling show differences in leaf anatomy, embryology and phytochemistry.

Illustrations. • Aucuba himalaica: Hooker’s Illustrations of Himalayan plants (1855). • Aucuba japonica (unvariegated form): Bot. Mag. 91 (1865). • Aucuba japonica: Bot. Mag. (1809). • Aucuba japonica (photo).

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: 5th March 2018.’.