| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Hugoniaceae Arn.

~ Linaceae-Hugonioideae.

Excluding Ctenolophonaceae.

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. The leaf lamina dorsiventral. Mucilaginous epidermis present. Stomata present; paracytic. The mesophyll with sclerenchymatous idioblasts.

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

The wood diffuse porous. The vessels medium; solitary, radially paired, and in radial multiples. The vessel end-walls scalariform and simple, or scalariform, or simple. The vessels without vestured pits; without spiral thickening. The axial xylem with tracheids; with vasicentric tracheids; with fibre tracheids; without septate fibres. The fibres without spiral thickening. The parenchyma apotracheal (confluent); wood not storied.

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 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, phytochemistry. 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 III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Malpighiales (as a synonym of Linaceae).

Species 40. Genera perhaps 5; Hugonia, plus Hebepetalum, Indorouchera, Philbornea, Roucheria.

General remarks. This compiled description offers several fairly obvious differences from Linaceae.

Illustrations. • Hugonia acuminata: Thonner. • Hugonia mystax: R. Wight (1840). • Hugonia brewerioides and H. coursiana: Fl. de Madagascar et des Comores 101 (1952). • Philbornea magnifolia, as Durandea: Hook. Ic. Pl. 29 (1906). • Roucheria contestiana, Hugonia montana: Pierre, Fl. Forestiere de la Cochinchine 3 (1889).

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: 8th June 2026. delta-intkey.com’.

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