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The families of flowering plants

L. Watson and M. J. Dallwitz

Sterculiaceae Vent.

Including Buettneriaceae auctt., Byttneriaceae R.Br., Chiranthodendreae (Cheiranthodendreae, Cheiranthodendraceae) A. Gray, Dombeyaceae (DC.) Bartling, Fremontieae (Fremontiaceae) J.G. Agardh, Helicteraceae J.G. Agardh, Hermanniaceae Berchtold & Presl, Lasiopetalaceae J.G. Agardh, Melochiaceae J.G. Agardh, Theobromeae (Theobromataceae) J.G. Agardh, Triplochitonaceae K. Schum.

Habit and leaf form. Trees and shrubs, or lianas, or herbs (rarely). ‘Normal’ plants. Self supporting, or climbing. Leptocaul, or pachycaul. Mesophytic, or xerophytic. Leaves alternate; petiolate; non-sheathing; simple, or compound; sometimes palmate. Lamina dissected, or entire; when dissected, often palmatifid; palmately veined, or pinnately veined; cross-venulate. Leaves stipulate. Stipules intrapetiolar; free of one another; caducous, or persistent. Leaf development not ‘graminaceous’. Domatia occurring in the family (known from 8 genera); manifested as pits (rarely), or pockets (mostly), or hair tufts.

Leaf anatomy. The leaf lamina generally dorsiventral. Mucilaginous epidermis present. Stomata usually mainly confined to one surface (the lower); anomocytic (usually), or paracytic (Reevesia). Hairs of numerous kinds present (in the family); eglandular and glandular; unicellular and multicellular. Complex hairs present; predominantly peltate and stellate (cf. Bombacaceae and Malvaceae). Adaxial hypodermis present, or absent. Lamina with secretory cavities, or without secretory cavities. Secretory cavities containing mucilage. The mesophyll containing mucilage cells (commonly, more widely didtributed than canals), or not containing mucilage cells; containing crystals. The crystals druses, or solitary-prismatic. Minor leaf veins without phloem transfer cells (Fremontodendron, Sterculia).

Axial (stem, wood) anatomy. Secretory cavities present (schizogenous and/or lysigenous), or absent; with mucilage. Cork cambium present; initially superficial. Nodes tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles, or comprising a ring of bundles (then the xylem traversed by wide rays, or in Brachychiton by wide sheaths of parenchyma); collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent (mostly), or present (Leptonychia). Secondary thickening developing from a conventional cambial ring. Primary medullary rays wide (beconing triangular when traversing the phloem).

The wood ring porous to diffuse porous. The vessels small, or medium (mostly), or large; mostly solitary, radially paired, and in radial multiples, or clustered, or in tangential arcs. The vessel end-walls simple. The vessels without vestured pits; with spiral thickening, or without spiral thickening. The axial xylem without fibre tracheids; with libriform fibres; without septate fibres. The fibres without spiral thickening. The parenchyma apotracheal, or paratracheal (perhaps exhibiting a subfamilial distinction). The secondary phloem stratified into hard (fibrous) and soft (parenchymatous) zones. ‘Included’ phloem absent. Tile cells present (Durio, Pterospermum and intermediate types, common in Buettnerieae), or absent. The wood storied, or partially storied.

Reproductive type, pollination. Plants hermaphrodite (usually), or monoecious, or polygamomonoecious.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (usually, sometimes cauliflorous); in cymes. The ultimate inflorescence units cymose. Inflorescences axillary (usually), or terminal, or leaf-opposed, or cauliflorous; complex cymes. Flowers regular (usually), or somewhat irregular; usually 5 merous; cyclic; tetracyclic to polycyclic. Floral receptacle developing an androphore (often), or with neither androphore nor gynophore. Free hypanthium absent.

Perianth with distinct calyx and corolla, or sepaline (corolla often absent or reduced); 5–10; 1 whorled, or 2 whorled; isomerous (usually). Calyx (3–)5; 1 whorled; polysepalous, or gamosepalous (usually briefly connate basally). Calyx lobes markedly longer than the tube. Calyx unequal but not bilabiate; usually persistent; valvate. Epicalyx absent. Corolla when present, 5; 1 whorled; polypetalous (the petals free of one another, but sometimes adnate to the androecial tube); contorted; regular. Petals clawed (usually), or sessile.

Androecium 5, or 10, or 25–500. Androecial members branched (commonly), or unbranched; when branched, maturing centrifugally; free of the perianth, or adnate (the staminal tube often attached to the petals); free of one another, or coherent (the inner whorl often united into a staminal tube); often 5 adelphous (with 5 bundles of 2–3(-10 or more)); (1–)2 whorled. The androecial bundles when bundled, alternating with the corolla members, or opposite the corolla members. Androecium exclusively of fertile stamens, or including staminodes. Staminodes when present, 2–15; external to the fertile stamens (the outer whorl when present staminodial); petaloid, or non-petaloid. Stamens 5, or 10–500; isomerous with the perianth to polystemonous; or bundles alternisepalous, or oppositisepalous. Anthers dehiscing via longitudinal slits (usually), or dehiscing via pores; extrorse; bilocular; tetrasporangiate. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Anther wall initially with one middle layer, or initially with more than one middle layer (1 or 2); of the ‘basic’ type, or of the ‘dicot’ type. Tapetum glandular. Pollen grains aperturate; 3 aperturate, or 4–9 aperturate; porate, or colporate (or colpoidate), or foraminate, or rugate; psilate, or scabrous (?); 2-celled (recorded in 14 genera).

Gynoecium (1–)5 carpelled, or 10–12 carpelled. Carpels isomerous with the perianth, or reduced in number relative to the perianth, or increased in number relative to the perianth. The pistil when syncarpous, (1–)5 celled, or 10–12 celled (rarely). Gynoecium apocarpous to syncarpous; eu-apocarpous to semicarpous, or synovarious, or synstylovarious, or eu-syncarpous, or synstylous; superior. Carpel apically stigmatic; when apocarpous/semicarpous or synstylous, 2–100 ovuled (to ‘many’). Placentation marginal. Ovary when syncarpous (1–)5 locular, or 10–12 locular (rarely). Gynoecium stylate. Styles 1, or 2; free, or partially joined. Stigmas dry type, or wet type; papillate (when dry), or non-papillate (when wet); Group II type, or Group IV type. Placentation usually axile. Ovules 2–50 per locule (to ‘many’); horizontal, or ascending; more or less apotropous (?); with ventral raphe, or with lateral raphe; arillate, or non-arillate; hemianatropous, or anatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing only after one has been fertilized. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Hypostase present. Endosperm formation nuclear. Embryogeny asterad.

Fruit fleshy, or non-fleshy (then leathery or woody); an aggregate, or not an aggregate. The fruiting carpel (apocarpous/syncarpous) dehiscent; a follicle, or samaroid. Fruit (when syncarpous) dehiscent, or indehiscent, or a schizocarp. Mericarps when schizocarpic, (2–)5, or 10–12; comprising berrylets, or comprising follicles, or comprising nutlets, or samaroid (?). Fruit (when syncarpous/non-schizocarpic) a capsule (usually), or capsular-indehiscent (woody). Capsules usually septicidal, or loculicidal. Seeds endospermic (usually), or non-endospermic (e.g. Cola). Endosperm oily, or not oily. Seeds with starch. Cotyledons 2; flat, or folded, or rolled. Embryo chlorophyllous (4/5); straight, or curved.

Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, phytochemistry. Anatomy non-C4 type (Pterospermum). Sugars transported as sucrose (in Pterocymbium and Sterculia). Cyanogenic, or not cyanogenic. Alkaloids present, or absent. Iridoids not detected. Saponins/sapogenins at least mostly absent. Proanthocyanidins present (usually), or absent; cyanidin. Flavonols present; kaempferol, or quercetin, or kaempferol and quercetin. Ellagic acid absent (9 species, 7 genera). Aluminium accumulation not found.

Geography, cytology. Sub-tropical to tropical. Pantropical and subtropical, extending to Japan and Southern Australia. X = (5-)20(-50)(?).

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Malviflorae; Malvales. Cronquist’s Subclass Dilleniidae; Malvales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; malvid; Order Malvales (as a synonym of Malvaceae?).

Species 700. Genera 68; Acropogon, Aethiocarpa, Ambroma (Abroma), Astiria, Ayenia, Brachychiton, Byttneria, Cheirolaena, Chiranthodendron, Cola, Commersonia, Corchoropsis, Cotylonychia (or Tiliaceae?), Dicarpidium, Dombeya, Eriolaena, Firmiana, Franciscodendron, Fremontodendron, Gilesia, Glossostemon, Guazuma, Guichenotia, Hannafordia, Harmsia, Helicteres, Helmiopsiella, Helmiopsis, Heritiera, Hermannia, Herrania, Hildegardia, Keraudrenia, Kleinhovia, Lasiopetalum, Leptonychia, Lysiosepalum, Mansonia, Maxwellia, Megatritheca, Melhania, Melochia, Neoregniella, Nesogordonia, Octolobus, Paradombeya, Paramelhania, Pentapetes, Pterocymbium, Pterospermum, Pterygota, Rayleya, Reevesia, Ruizia, Rulingia, Scaphium, Scaphopetalum, Seringia, Sterculia, Theobroma, Thomasia, Trichostephania, Triplochiton, Trochetia, Trochetiopsis, Uladendron, Ungeria, Waltheria.

General remarks. Bayer et al. (1999) expanded Malvaceae to include Bombacaceae, Sterculiaceae and Tiliaceae, consequent on a combined analysis of plastid atpB and rbcL DNA sequences. Comparisons of descriptions compiled for this package show Sterculiaceae differing from Malvaceae sensu stricto (q.v.) in the unequal calyx members; androecium details, including extrorse, bilocular, tetrasporangiate anthers with glandular tapetum; and (in so far as limited sampling can be relied upon) ovules with polar nuclei fusing only after one has neen fertilized.

Economic uses, etc. Chocolate (cacao) is obtained from the fermented seeds (‘beans’) of Theobroma cacao. A few genera supply ornamentals (e.g. Brachychiton).

Illustrations. • Technical details: Sterculia. • Technical details: Byttneria, Hermannia, Theobroma. • Technical details: Helicteres (Lindley). • Astiria rosea: Bot. Reg. 1844, 49. • Hermannia althaeifolia: Bot. Mag. 307, 1795. • Lasiopetalum bracteatum: as Corethrostylis bracteata, Bot. Reg. 1844, 47. • Mahernia pinnata: Bot. Mag. 277, 1794. • Reevesia thyrsoidea: Bot. Reg. 1236, 1829. • Sterculia lanceolata: Bot. Reg. 1256, 1829. • Trochetia triflora: as T. grandiflora, Bot. Reg. 1844, 21.

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: 19th October 2016.’.