Family Helwingiaceae

Helwingiaceae Decaisne

~ Cornaceae

Habit and leaf form. Glabrous shrubs. Leaves alternate (to subopposite); spiral; petiolate; simple. Lamina entire; ovate lanceolate, or ovate; pinnately veined; cross-venulate. Leaves stipulate (the stipules often branched). Stipules intrapetiolar (on the petiole); free of one another; caducous. Lamina margins serrate (serrulate).

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

Lamina without secretory cavities. The mesophyll without calcium oxalate crystals. Minor leaf veins without phloem transfer cells.

Stem anatomy. Secretory cavities absent. Nodes unilacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem without fibre tracheids; with libriform fibres (occasionally septate). Vessel end-walls scalariform. Wood parenchyma apotracheal.

Reproductive type, pollination. Plants dioecious.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in umbels. Inflorescences epiphyllous (from the upper side of the midrib); small epiphyllous umbels, the male flowers sometimes long pedicellate, the females shortly so. Flowers small; regular; 3–4(–5) merous; cyclic. Free hypanthium absent.

Perianth petaline (as described by Airy Shaw); 3–4(–5); 1 whorled. Corolla 3–4(–5); 1 whorled; polypetalous; valvate.

Androecium 3–4(–5). Androecial members free of the perianth; free of one another; 1 whorled. Androecium of male flowers, exclusively of fertile stamens. Stamens 3–4(–5); isomerous with the perianth; (theoretically) oppositisepalous; alternating with the corolla members; filantherous (inserted outside the flat angled disk). Anthers dehiscing via longitudinal slits; introrse. Pollen grains aperturate; 3 aperturate; colporate.

Gynoecium 3–4 carpelled. Carpels reduced in number relative to the perianth to isomerous with the perianth. The pistil 3–4 celled. Gynoecium syncarpous; synstylovarious; inferior. Ovary 3–4 locular. Epigynous disk present (passing into the style). Gynoecium stylate. Styles 1; apical; shorter than the ovary. Stigmas 3–4 (recurved). Placentation apical. Ovules 1 per locule; pendulous; apotropous; with dorsal raphe; anatropous.

Fruit fleshy; indehiscent; a drupe. The drupes with separable pyrenes (3–4). Fruit 3–4 seeded. Seeds endospermic. Embryo well differentiated (small). Embryo straight.

Physiology, biochemistry. Iridoids not detected.

Geography, cytology. Holarctic. Temperate. Eastern Himalayas to Japan and Formosa. X = 19.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli (?). Dahlgren’s Superorder Araliiflorae; Araliales. Cronquist’s Subclass Rosidae; Cornales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; campanulid; Order Aquifoliales.

Species 5. Genera 1; only genus, Helwingia.

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.
• Technical details Helwingia (Lindley).
• Helwingia.