Family Geniostomaceae

Geniostomaceae L. Struwe and V.A. Albert

~ Loganiaceae sensu lato

Habit and leaf form. Small, glabrous trees and shrubs; non-laticiferous and without coloured juice. Plants non-succulent. 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.

Stem anatomy. Young stems cylindrical. Internal phloem present. Secondary thickening anomalous; from a single cambial ring. ‘Included’ phloem present. Xylem without fibre tracheids; with libriform fibres (fibres mostly septate). Vessel end-walls horizontal to oblique (‘often short’); simple (mostly), or reticulately perforated (a few, irregularly, in Geniostoma), or scalariform (a few, in Labordia). Vessels with vestured pits. Primary medullary rays mixed wide and narrow (uniseriate and multiseriate). Wood diffuse porous; not storied; parenchyma apotracheal and paratracheal.

Reproductive type, pollination. Fertile flowers functionally male, or functionally female. 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’; terminal, or axillary; when aggregated, in cymes. The ultimate inflorescence unit 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, biochemistry. Alkaloids present (Geniostoma australianum), or absent. Iridoids detected; ‘Route I’ type. Verbascosides not detected. Cornoside not detected.

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 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Gentianales (as a synonym of Loganiaceae).

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

Leeuwenberg 1980, under Loganiaceae. Perhaps justifiably removed from Loganiaceae, and awarded family rank by Struwe and Albert (1994) in consequence of a cladistic study of Gentianales. In customary cladistic style, they provided an inadequate description of the new family (see comment under Loganiaceae). On the basis of the above much extended description, Geniostomaceae appear much closer to Gentianaceae and many other tenuinucellate families than to Apocynaceae and Rubiaceae. See comments under Loganiaceae.