Family Eucommiaceae

Eucommiaceae Van Tiegh.

Habit and leaf form. Trees; laticiferous. Leaves deciduous; alternate; petiolate; simple. Lamina entire; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins serrate, or dentate.

General anatomy. Plants with laticifers (articulated, in the phloem and cortex). The laticifers in leaves and in stems.

Leaf anatomy. Stomata present; anomocytic.

Lamina dorsiventral.

Stem anatomy. Cork cambium present; initially superficial. Nodes unilacunar. Secondary thickening developing from a conventional cambial ring. Xylem with tracheids; with vessels. Vessel end-walls oblique; simple. Wood parenchyma apotracheal. Sieve-tube plastids S-type.

Reproductive type, pollination. Plants dioecious. Pollination anemophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. Inflorescences intercalary; consisting of shortly pedicellate flowers solitary in the axils of bracts, these crowded at the bases of distally leafy shoots (cf. Euptelea). Flowers bracteate; ebracteolate; small; regular. Hypogynous disk absent.

Perianth absent.

Androecium in the male flowers, (5–)6–10(–12). Androecial members free of one another. Androecium exclusively of fertile stamens. Stamens (5–)6–10(–12); very shortly filantherous. Anthers linear basifixed; non-versatile; dehiscing via longitudinal slits; tetrasporangiate; appendaged. The anther appendages apical (by apical prolongation of the connective). Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Anther wall initially with one middle layer, or initially with more than one middle layer. Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colporate (with poorly developed pores); 2-celled.

Gynoecium 2 carpelled. The pistil 1 celled. Gynoecium syncarpous (but pseudomonomerous); synstylovarious; superior. Ovary 1 locular (by abortion); sessile. Gynoecium very shortly stylate (within the V-shaped ovary apex). Styles 1; shorter than the ovary (very short). Stigmas 2 (unequal). Placentation apical. Ovules in the single cavity 2; pendulous; apotropous; with dorsal raphe; collateral; anatropous; unitegmic; weakly crassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating. Synergids pear-shaped. Endosperm formation cellular. Embryogeny solanad.

Fruit non-fleshy; indehiscent; a samara (somewhat elmlike); 1 seeded. Seeds endospermic. Embryo well differentiated (large). Cotyledons 2. Embryo straight.

Seedling. Germination phanerocotylar.

Physiology, biochemistry. Not cyanogenic. Alkaloids absent (2 species). Iridoids detected (aucubin); ‘Route II’ type. Verbascosides not detected. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol and quercetin. Ellagic acid absent. Arbutin absent. Saponins/sapogenins present.

Geography, cytology. Holarctic. Temperate. China. 2n = 34.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Corniflorae; Cornales. Cronquist’s Subclass Hamamelidae; Eucommiales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Garryales.

Species 1. Genera 1; only genus, Eucommia.