| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Aquilariaceae R. Br.

~ Thymelaeaceae.

Habit and leaf form. Trees. Leaves alternate; flat; petiolate; non-sheathing; not gland-dotted; simple. Lamina entire; pinnately veined. Leaves exstipulate. Lamina margins entire.

Leaf anatomy. The leaf lamina dorsiventral. The mesophyll with sclerenchymatous idioblasts, or without sclerenchymatous idioblasts.

Axial (stem, wood) anatomy. Cork cambium present; initially superficial. Primary vascular tissues in a cylinder, without separate bundles; collateral (Microsemma and Solmsia), or bicollateral (usually). Internal phloem present (usually), or absent (Microsemma and Solmsia). Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring, or anomalous (commonly). The anomalous secondary thickening from a single cambial ring. Primary medullary rays narrow.

The wood diffuse porous. The vessel end-walls simple. The vessels with vestured pits. The parenchyma paratracheal (usually), or apotracheal and paratracheal (Microsemma). ‘Included’ phloem commonly present. The wood not storied.

Reproductive type, pollination. Unisexual flowers present, or absent. Plants hermaphrodite, or monoecious, or polygamomonoecious (?).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in umbels, or in corymbs, or in fascicles, or in panicles. Inflorescences terminal and axillary; subsessile axillary umbels or fascicles, these sometimes subpaniculate. Flowers ebracteate; regular; cyclic; tetracyclic, or pentacyclic. Free hypanthium present. Hypogynous disk absent.

Perianth with distinct calyx and corolla (but the corolla often scalelike), or sepaline; (8–)10; 1 whorled, or 2 whorled; isomerous (when corolla present, but the petal scales sometimes bilobed). Calyx (4–)5; 1 whorled; gamosepalous; (4–5) blunt-lobed; campanulate, or funnel-shaped, or tubular, or hypocrateriform; regular; imbricate. Corolla when present, (4–)5, or (8–)10; 1 whorled; polypetalous, or gamopetalous (the petals represented by scales at the mouth of the hypanthium/calyx tube, sometimes connate at the base, sometimes bilobed).

Androecium (4–)5, or (8–)10. Androecial members free of the perianth (borne on the hypanthium); all equal, or markedly unequal; free of one another; 1 whorled, or 2 whorled. Androecium exclusively of fertile stamens. Stamens (4–)5, or (8–)10; isomerous with the perianth, or diplostemonous; when in two cycles, oppositisepalous (i.e. the upper, outer cycle opposite the sepals); filantherous (the filaments short). Anthers dehiscing via longitudinal slits; introrse; tetrasporangiate. Pollen grains aperturate; 4–12 aperturate; foraminate.

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled, or 2 celled. Gynoecium syncarpous (but tending to pseudomonomery); eu-syncarpous; superior. Ovary 2 locular (sometimes incompletely so); subsessile to stipitate. Gynoecium non-stylate to stylate. Styles when present, 1; apical; much shorter than the ovary. Stigmas 1; large, capitate, or subpeltate. Placentation axile to apical. Ovules 1 per locule; funicled; pendulous; hemianatropous, or anatropous; bitegmic; crassinucellate. Endosperm formation nuclear.

Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Fruit 1 seeded, or 2 seeded. Seeds endospermic. Embryo well differentiated. Cotyledons 2. Embryo straight.

Geography, cytology. Tropical. Eastern tropical Africa to New Caledonia.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Malviflorae; Thymelaeales. Cronquist’s Subclass Rosidae; Myrtales. APG III core angiosperms; core eudicot; Superorder Rosanae; malvid. APG IV Order Malvales (as a synonym of Thymelaeaceae).

Species 32. Genera 6; Aquilaria, Gyrinops, Gyrinopsis, Microsemma, Octolepis, Solmsia.

General remarks. Seemingly separable from Thymelaeaceae sensu stricto only on habit and the dehiscent, capsular fruits.

Economic uses, etc. Timber and paper fibre from Gyrinops, incense from Aquilaria.

Illustrations. • Aquilaria agallochum: Lindley. • Gyrinops walla: Wight, Ic. Pl. Ind. Orient. 5 (1846). • Gyrinops walla: Hook. Ic. Pl. 1 (1837). • Octolepis casearia, as O. flamignii: Wildeman, Ann. du Musée du Congo, Botanique 3 (1909).

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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