| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Ixonanthaceae Planch. ex Klotzsch

~ Simaroubaceae.

Excluding Irvingiaceae (= Simaroubaceae p.p.).

Habit and leaf form. Trees, or shrubs; non-laticiferous, without coloured juice. Leaves alternate; spiral, or distichous (then asymmetric); petiolate; non-sheathing; without marked odour; simple; epulvinate. Lamina entire; pinnately veined; cross-venulate. Leaves stipulate (the stipules small), or exstipulate. Lamina margins entire, or serrate, or dentate. Leaf development not ‘graminaceous’.

Leaf anatomy. Stomata present; paracytic.

Axial (stem, wood) anatomy. Secondary thickening developing from a conventional cambial ring. Primary medullary rays mixed wide and narrow.

The vessel end-walls simple. The axial xylem with fibre tracheids; without libriform fibres. The parenchyma apotracheal.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite (mostly).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes, or in racemes, or in panicles (thyrses). Inflorescences terminal, or axillary. Flowers small; regular (or nearly so); not resupinate; neither papilionaceous nor pseudo-papilionaceous; usually 5 merous. Free hypanthium absent. Hypogynous disk present; intrastaminal; annular (to cupular, well developed).

Perianth with distinct calyx and corolla; (8–)10; 2 whorled; isomerous. Calyx (4–)5; 1 whorled; polysepalous, or gamosepalous (then connate only basally). Calyx lobes markedly longer than the tube. Calyx regular; imbricate, or contorted. Corolla (4–)5; 1 whorled; polypetalous; imbricate, or contorted; persistent (often, and becoming indurated), or deciduous (?).

Androecium 5–10–20. Androecial members unbranched; free of the perianth (sometimes adnate to the intrastaminal disk); all equal, or markedly unequal; free of one another. Androecium exclusively of fertile stamens. Stamens 5, or 10, or 20; isomerous with the perianth, or diplostemonous, or polystemonous; with the filaments sigmoid-folded in bud; filantherous (the filaments expanded at the base). Anthers not becoming inverted during development; dehiscing via longitudinal slits; tetrasporangiate. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colporate; 2-celled.

Gynoecium 2 carpelled, or (4–)5 carpelled. Carpels reduced in number relative to the perianth, or isomerous with the perianth. The pistil 2–10 celled (?). Gynoecium syncarpous; eu-syncarpous; superior. Ovary 2 locular, or (4–)5 locular (sometimes unilocular towards the top, the partitions falling short, and sometimes with secondary false septa). Locules secondarily divided by ‘false septa’, or without ‘false septa’. Gynoecium stylate. Styles 1; apical. Stigmas 1; capitate. Placentation axile to apical. Ovules 1 per locule, or 2 per locule; funicled; pendulous; arillate, or non-arillate; anatropous; bitegmic; crassinucellate (?). Endosperm formation nuclear (?).

Fruit non-fleshy; dehiscent; a capsule. Capsules septicidal, or septicidal and loculicidal. Seeds scantily endospermic; winged, or wingless.

Physiology, phytochemistry. Mustard-oils absent. Proanthocyanidins present. Ellagic acid present.

Geography, cytology. Tropical. Pantropical.

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.

Species about 30. Genera 4, or 5; Allantospermum(?), Cyrillopsis, Ixonanthes, Ochthocosmus, Phyllocosmus.

General remarks. This is a poor description. In any case, practical taxonomic applications of recent notions on the dispositions of assorted genera previously referred to Simaroubaceae will necessitate thorough overhaul of family descriptions as compiled in this package (cf. Irvingiaceae, Kirkiaceae, Picramniaceae, Simaroubaceae, Surianaceae, Stylobasiaceae).

Illustrations. • Ixonanthes chinensis: Trans. Linn. Soc Lond. 21 (1855). • Ixonanthes chinensis (Hutchinson).

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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