| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Loasaceae Spreng.

Including Cevalliaceae Griseb., Gronoviaceae Endlicher

Habit and leaf form. Small trees (rarely), or shrubs (sometimes), or herbs (mostly, mostly bristly); non-laticiferous, without coloured juice. Plants non-succulent. Annual, or perennial (more often); without conspicuous aggregations of leaves. Self supporting, or climbing; sometimes herbaceous stem twiners; twining clockwise (Scyphanthus), or twining clockwise and twining anticlockwise (variable, Loasa). Leaves alternate, or opposite; long petiolate to sessile; gland-dotted, or not gland-dotted; simple, or compound; when compound, ternate (e.g., in Nasa triphylla), or pinnate; imparipinnate. Lamina when simple, dissected, or entire; when simple-dissected, variously pinnatifid, or palmatifid, or much-divided; pinnately veined, or palmately veined; cross-venulate. Leaves ‘falsely’ stipulate, or exstipulate.

Leaf anatomy. The leaf lamina bifacial to centric (mostly), or dorsiventral. Stomata present; anomocytic. Hairs present (represented by diverse kinds, generally coarse, silicified and often calcified); eglandular and glandular; unicellular and multicellular. Unicellular hairs branched. Multicellular hairs uniseriate; simple. Complex hairs absent. Urticating hairs commonly present (these unicellular, elongated, silicified and brittle, filled with a yellowish irritant causing serious injuries to animals), or absent. Cystoliths lime or silica present (commonly, at the bases of hairs), or absent. Minor leaf veins without phloem transfer cells (Blumenbachia).

Axial (stem, wood) anatomy. Primary vascular tissues in a cylinder, without separate bundles, or comprising a ring of bundles; collateral. Cortical bundles absent. Medullary bundles absent. Secondary thickening absent, or developing from a conventional cambial ring.

The vessel end-walls simple. The axial xylem with fibre tracheids. The wood partially storied (VI).

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present, or absent (?). Nectar secretion from the androecium (from staminodes).

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’ (more often). The ultimate inflorescence units cymose. Flowers regular; cyclic. Floral receptacle markedly hollowed. Free hypanthium present (‘the petals inserted on the calyx’).

Perianth with distinct calyx and corolla; (8–)10(–14); 2 whorled; isomerous. Calyx (4–)5(–7); polysepalous; regular; persistent; imbricate, or contorted. Corolla (4–)5(–7) (or 10 when supplemented by petaloid staminodes); polypetalous, or gamopetalous; induplicate valvate; yellow (usually), or white (rarely), or red (rarely). Petals clawed, or sessile.

Androecium 5 (Gronovioideae), or 10–100 (usually ‘many’). Androecial members branched (sometimes, in antepetalous bundles), or unbranched; when determinable, maturing centripetally (Mentzelioideae), or maturing centrifugally (Loasoideae); free of the perianth, or adnate (sometimes with nearly sessile anthers borne on the corolla tube); free of one another, or coherent (sometimes basally connate into a short tube, or into antepetalous bundles). The androecial bundles when bundled, opposite the corolla members. Androecium exclusively of fertile stamens, or including staminodes (often). Staminodes petaloid (sometimes), or non-petaloid, or petaloid and non-petaloid (and sometimes nectariferous, sometimes as in Loasa and Blumenbachia, three or more of them being united to form a large, coloured nectary whose mouth is towards the centre of the flower and is partly obstructed by the other staminodes). Stamens 5, or 10–100 (to ‘many’); reduced in number relative to the adjacent perianth to polystemonous. Anthers dehiscing via longitudinal slits; tetrasporangiate; unappendaged. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colporate; 2-celled.

Gynoecium 1 carpelled (ostensibly, in Grovonoideae), or 3–5(–7) carpelled. The pistil 1 celled, or 2 celled, or 3–7 celled (rarely). Gynoecium syncarpous (but with pseudomonomery in the Gronovioideae); synstylovarious to eu-syncarpous; partly inferior to inferior (often ribbed, the ribs sometimes spiralled). Ovary 1 locular (usually, often with more or less deeply intruded placentas, and pseudomonomerous in Gronovioideae), or 2 locular (rarely, fully partitioned). Gynoecium stylate. Styles 1; apical. Placentation when unilocular, parietal (usually), or apical (pseudomonomerous Gronovioideae); when plurilocular, i.e. rarely, axile. Ovules in the single cavity 1–100 (to ‘many’); 1–50 per locule (to ‘many’); non-arillate; anatropous, or hemianatropous; unitegmic; tenuinucellate. Endothelium differentiated. Embryo-sac development Polygonum-type. Antipodal cells formed; 3; not proliferating; persistent (in a shallow pouch). Endosperm formation cellular (with chalazal and micropylar haustoria). Endosperm haustoria present; chalazal and micropylar. Embryogeny solanad.

Fruit non-fleshy; dehiscent (usually), or indehiscent; a capsule (usually, straight or spirally twisted), or capsular-indehiscent, or achene-like, or a nut. Capsules usually septicidal, or loculicidal. Seeds copiously endospermic (usually), or non-endospermic (endosperm scanty or wanting in Gronovioideae). Endosperm oily. Embryo well differentiated. Cotyledons 2; flat. Embryo achlorophyllous (1/1); straight, or curved (spathulate).

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Petalonyx. Not cyanogenic. Alkaloids absent (3 species). Iridoids commonly detected; ‘Route I’ type (normal and seco). Saponins/sapogenins absent. Proanthocyanidins absent. Flavonols present; kaempferol, or quercetin. Ellagic acid absent (2 genera, 2 species). Aluminium accumulation not found.

Geography, cytology. Holarctic, Paleotropical, and Neotropical. Temperate to tropical. Mostly tropical or subtropical, southern U.S.A., Central and South America, with only Fissenia (Kissenia) in Arabia and Southwest Africa. X = 7–15(+).

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Loasiflorae; Loasales. Cronquist’s Subclass Dilleniidae; Violales. APG III core angiosperms; core eudicot; Superorder Asteranae. APG IV Order Cornales.

Species about 300. Genera 15, or 20 (depending on interpretation of Loasa sensu lato, cf. Weigend 2006); Aosa, Blumenbachia, Caiophora, Cevallia, Eucnide, Fuertesia, Grausa, Gronovia, Klaprothia, Loasa sensu lato (including Chichicaste, Huidobria, Kissenia, Nasa, Preslophytum, Xylopodia), Mentzelia, Petalonyx, Plakothira, Schismocarpus, Scyphanthus.

General remarks. A major 2006 revision by Weigend (Taxon 55) has yet to be accounted for here.

Illustrations. • Le Maout and Decaisne: Caiophora, Loasa. • Le Maout and Decaisne: Bartonia (= Mentzelia). • Aosa rupestris, as Loasa: Hook. Ic. Pl. 7–8 (1844). • Blumenbachia lateritia: as Loasa, Bot. Reg. XXIV, 22 (1838). • Blumenbachia multifida: Bot. Mag. 64 (1837). • Caiophora carinoides (as Illairea): Bot. Mag. 83 (1857). • Caiophora chuquitensis, as Blumenbachia: Bot. Mag 101 (1875). • Caiophora contorta: Bot. Mag. 100 (1874). • Caiophora coronata: Bot. Mag. 133 (1907). • Caiophora pentlandii (as Loasa): Bot. Mag. 70 (1844). • Cevallia sinuata: Hook. Ic. Pl. 3 (1840). • Eucnide bartonioides, as Microsperma: Bot. Mag. 76 (1850). • Eucnide lobata, as Microsperma: Hook. Ic. Pl. 3 (1840). • Grausa lateritia (as Loasa): Bot. Mag. 65 (1838). • Loasa acanthifolia: Bot. Reg. 785, 1824. • Loasa prostrata: Bot. Mag. 105 (1879). • Nasa urens (as Loasa ambrosiifolia): Bot. Reg. 1390, 1830. • cf. Mentzelia apera, as Bartonia albicaulis: Lindley. • Mentzelia hispida: Bot. Mag. 59 (1832). • Mentzelia lindleyi: as Bartonia aurea, Bot. Reg 1831 (1836). • Mentzelia lindleyi (as Bartonia aurea): Bot. Mag. 65 (1838). • Mentzelia nuda (as Bartonia): Bot. Mag. 90 (1864). • Nasa picta (as Loasa): Bot. Mag. 75 (1849). • Nasa triphylla (as Loasa vulcanica): Bot. Mag. 105 (1879). • Presliophytum incanum (as Loasa incana): Bot. Mag. 58 (1831). • Scyphanthus elegans (as Grammatocarpus volubilis): (Bot. Mag. 84 (1858). • Leaf hairs of Caiophora, Eucnide, Loasa, and Petalonyx (Solereder, 1908).

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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