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. Plants non-succulent. 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. Leaves without a persistent basal meristem. Domatia recorded (8 genera); represented by pits (rarely), or pockets (mostly), or hair tufts.

Leaf anatomy. Mucilaginous epidermis present. Stomata anomocytic (usually), or paracytic (Reevesia). Hairs present; eglandular and glandular; unicellular and multicellular. Complex hairs present; peltate and stellate.

Adaxial hypodermis present, or absent. Lamina generally dorsiventral; with secretory cavities, or without secretory cavities. Secretory cavities containing mucilage. The mesophyll containing mucilage cells, or not containing mucilage cells. Minor leaf veins without phloem transfer cells (Fremontodendron, Sterculia).

Stem anatomy. Secretory cavities present (schizogenous and lysigenous), or absent; with mucilage. Cork cambium present; initially superficial. Nodes tri-lacunar. Primary vascular tissue in a cylinder, without separate bundles. Cortical bundles absent. Medullary bundles absent (mostly), or present (Leptonychia). Internal phloem absent. Secondary thickening developing from a conventional cambial ring. The secondary phloem stratified into hard (fibrous) and soft (parenchymatous) zones. ‘Included’ phloem absent. Xylem without fibre tracheids; with libriform fibres; with vessels. Vessel end-walls simple. Vessels without vestured pits. Tile cells present (Durio, Pterospermum and intermediate types). Wood ring porous to diffuse porous; storied, or partially storied; parenchyma apotracheal, or paratracheal (perhaps exhibiting a subfamilial distinction).

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 terminal inflorescence unit 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; 2-celled.

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

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 (1998) Eudicot; core Eudicot; Rosid; Eurosid II; Malvales. 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.

Bayer et al. expand Malvaceae to include Bombacaceae, Sterculiaceae and Tiliaceae, consequent on a combined analysis of plastid atpB and rbcL DNA sequences.

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 (Byttneria, Hermannia, Theobroma). • Technical details (Sterculia). • Technical details (Helicteres).