Family Aucubaceae

Aucubaceae J.G. Agardh

~ Cornaceae

Habit and leaf form. Small herbs, or shrubs. Plants non-succulent. Leaves evergreen; opposite; flat; leathery; petiolate; somewhat connate; not gland-dotted; simple. Lamina entire; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins entire, or dentate. Vegetative buds scaly. Leaves without a persistent basal meristem.

Leaf anatomy. Stomata present; mainly confined to one surface (the lower); anomocytic.

Lamina dorsiventral. Minor leaf veins without phloem transfer cells.

Stem anatomy. Nodes tri-lacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with vessels. Wood parenchyma paratracheal.

Reproductive type, pollination. Plants dioecious.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. The ultimate inflorescence unit 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, biochemistry. Not cyanogenic. Iridoids detected; ‘Route II’ type (+decarb.). Verbascosides not detected. 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 (1998) Eudicot; core Eudicot; Asterid; Euasterid I. APG 3 (2009) Order: Garryales.

Species 3. Genera 1; only genus, Aucuba.

This family exemplifies 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. This is interesting, given that the latter evidently represent a major divergence in the Dicot line of descent (cf.Young and Watson 1970, Chase et al. 1993).

Illustrations.
• Aucuba japonica (photo).

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