Habit and leaf form. Lianas. Climbing; scrambling (the lower inflorescence branches modified into hooks). Leaves alternate; simple. Lamina entire. Leaves stipulate. Stipules caducous.
Leaf anatomy. Mucilaginous epidermis present. Stomata present; paracytic.
Lamina dorsiventral. The mesophyll with sclerencymatous idioblasts.
Stem anatomy. Nodes tri-lacunar. Secondary thickening developing from a conventional cambial ring. Vessel end-walls scalariform and simple, or scalariform, or simple. Wood parenchyma apotracheal (confluent).
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in racemes, or in spikes, or in panicles. Inflorescences terminal, or axillary. Flowers small to large; somewhat irregular, or very irregular. The floral irregularity involving the perianth (the calyx only), or involving the androecium. Flowers neither papilionaceous nor pseudo-papilionaceous; 5 merous. Free hypanthium absent. Hypogynous disk present; extrastaminal; of separate members (represented by 2–5 glands).
Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous (the sepals commonly more or less unequal); imbricate. Corolla 5; 1 whorled; polypetalous; contorted; regular; deciduous (fugacious).
Androecium 10, or 15. Androecial members free of the perianth; usually markedly unequal; coherent (the filaments connate for much of their length, forming a tube); 1 adelphous. Androecium exclusively of fertile stamens, or including staminodes (? — the extrastaminal glands). Staminodes (the glands) 2–5; external to the fertile stamens. Stamens 10, or 15; diplostemonous, or triplostemonous; both alternating with and opposite the corolla members. Anthers dehiscing via longitudinal slits. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colporate.
Gynoecium 2–5 carpelled. Carpels reduced in number relative to the perianth to isomerous with the perianth. The pistil 2–5 celled. Gynoecium syncarpous; synovarious, or synstylovarious; superior. Ovary 2–5 locular (sometimes with the partitions not quite reaching the summit). Locules without ‘false septa’. Gynoecium stylate. Styles 1, or 2–5; free, or partially joined. Placentation axile to apical. Ovules 2 per locule; pendulous; epitropous (the micropyle directed upwards and outwards); with ventral raphe; with a placental obturator; anatropous; bitegmic; crassinucellate.
Fruit fleshy; indehiscent; a drupe. Seeds scantily endospermic, or non-endospermic. Embryo well differentiated. Cotyledons 2. Embryo slightly curved, or straight.
Physiology, biochemistry. Saponins/sapogenins present.
Geography, cytology. Paleotropical. Sub-tropical to tropical. Tropical Africa, Madagascar, Indomalaysia, New Caledonia. X = 12, 13.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rutiflorae; Geraniales. Cronquist’s Subclass Rosidae; Linales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Malpighiales (as a synonym of Linaceae).
Species 40. Genera perhaps 5; Hugonia, plus Hebepetalum, Indorouchera, Philbornea, Roucheria.
• Technical details: Hugonia (Thonner).