| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Geniostomaceae L. Struwe & V.A. Albert

~ Loganiaceae sensu lato.

Habit and leaf form. Small, glabrous trees and shrubs; non-laticiferous, without coloured juice. Leaves opposite; ‘herbaceous’, or leathery; petiolate to sessile; connate to not connate; simple. Lamina entire; pinnately veined; cross-venulate. Leaves stipulate, or exstipulate (then the stipules represented by a line joining the opposite leaf bases). Stipules interpetiolar, or intrapetiolar; with colleters (?), or without colleters (recorded on the calyx).

Leaf anatomy. Extra-floral nectaries absent. Hairs present, or absent; eglandular. Complex hairs absent. The mesophyll without raphides.

Axial (stem, wood) anatomy. Young stems cylindrical. Internal phloem present. Secondary thickening anomalous. The anomalous secondary thickening from a single cambial ring. Primary medullary rays mixed wide and narrow (uniseriate and multiseriate).

The wood diffuse porous. The vessel end-walls horizontal to oblique (‘often short’); simple (mostly), or reticulately perforated (a few, irregularly, in Geniostoma), or scalariform (a few, in Labordia). The vessels with vestured pits. The axial xylem without fibre tracheids; with libriform fibres; including septate fibres (most of them). The parenchyma apotracheal and paratracheal. ‘Included’ phloem present. The wood not storied.

Reproductive type, pollination. Unisexual flowers present. Plants monoecious, or dioecious, or gynodioecious (Geniostoma s. str.). Female flowers with staminodes. Gynoecium of male flowers pistillodial. Plants homostylous, or heterostylous (sometimes in Geniostoma).

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when solitary, terminal, or axillary; when aggregated, in cymes. The ultimate inflorescence units cymose. Inflorescences terminal, or axillary, or leaf-opposed (?). Flowers bracteate (bracts scale- or sepal-like); regular; 5 merous. Free hypanthium absent. Hypogynous disk absent.

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous (or almost so), or gamosepalous; toothed; unequal but not bilabiate, or regular; persistent; non-accrescent; imbricate. Corolla 5; 1 whorled; gamopetalous (glabrous to densely pubescent within); imbricate, or contorted; rotate, or campanulate, or hypocrateriform; regular; green to white (Geniostoma), or white to orange (or greenish, Labordia).

Androecium 5. Androecial members adnate (to the mouth of the corolla); free of one another; 1 whorled. Stamens 5; inserted in the throat of the corolla tube; isomerous with the perianth; oppositisepalous; alternating with the corolla members; filantherous. Filaments not appendiculate. Anthers dorsifixed; dehiscing via longitudinal slits; introrse (at least in Geniostoma); appendaged (often, at least in Geniostoma), or unappendaged. The anther appendages apical. Pollen grains aperturate; (2–)3(–4) aperturate; porate (photos showing slight but detectable annuli).

Gynoecium 2 carpelled, or 3 carpelled (often, in Labordia). Carpels reduced in number relative to the perianth. The pistil 2 celled, or 3 celled. Gynoecium syncarpous; synovarious to eu-syncarpous; superior. Ovary 2 locular, or 3 locular. Gynoecium median (?). Ovary sessile (?). Gynoecium stylate. Styles 1–3; partially joined; apical. Stigmas 1–3; clavate, or capitate. Placentation axile (the placentas not bilobed). Ovules 15–50 per locule (‘many’); anatropous, or amphitropous (?); unitegmic; tenuinucellate. Endothelium not differentiated.

Fruit non-fleshy; dehiscent; a capsule (the pericarp thick and woody). Capsules septicidal and valvular (the 2(–3) valves breaking away to expose the placentas). Fruit 25–100 seeded (‘many’). Seeds endospermic; not conspicuously hairy; wingless. Embryo well differentiated. Cotyledons 2. Embryo straight.

Physiology, phytochemistry. Alkaloids present (Geniostoma australianum), or absent. Verbascosides not detected. Cornoside not detected. Iridoids detected; ‘Route I’ type.

Geography, cytology. Paleotropical, Australian, and Antarctic. Temperate to tropical. Malesia, Australia, New Zealand, Tahiti, Japan, and (Labordia) Hawaii. 2n= 40(Geniostoma, about 80 (Labordia. Supposed basic chromosome number of family: 10. Ploidy levels recorded: 4 and 8.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Gentianiflorae; Gentianales. Cronquist’s Subclass Asteridae; Gentianales. APG III core angiosperms; core eudicot; Superorder Asteranae; lamiid. APG IV Order Gentianales (as a synonym of Loganiaceae).

Species about 60. Genera 1, or 2; Geniostoma, Labordia (= Geniostoma).

General remarks. See Leeuwenberg 1980, under Loganiaceae. Removed from Loganiaceae and awarded family rank by Struwe and Albert (1994) in consequence of a cladistic study of Gentianales; but in customary cladistic style, they provided an inadequate description of the new family (see comment under Loganiaceae). The above, much extended description has Geniostoma differing dubiously from Loganiaceae sensu stricto only in recorded details of wood anatomy, pollen morphology, and the supposed basic chromosome numbers. See comments under Loganiaceae.

Illustrations. • Geniostoma rupstre var. ligustrifolium: M. Smith, in Cheeseman et al. (1914). • Geniostoma rupestre var. ligustrifolium, as G. ligustrifolium: Hook. Ic. Pl. 5–6 (1842–3).

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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