Family Sphaerosepalaceae

Sphaerosepalaceae Van Tiegh.

Alternatively Rhopalocarpaceae Hemsl.

Habit and leaf form. Trees, or ‘arborescent’, or shrubs. Leaves deciduous; alternate; simple. Lamina entire; pinnately veined, or palmately veined (then three veined). Leaves stipulate. Stipules intrapetiolar; caducous (large).

Leaf anatomy. Stomata present; anomocytic, or anisocytic, or cyclocytic.

The mesophyll containing mucilage cells.

Stem anatomy. Cortical bundles absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with tracheids. Vessel end-walls simple. Vessels without vestured pits. Wood partially storied (VP, Rhopalocarpus).

Reproductive type, pollination. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. The ultimate inflorescence unit cymose. Inflorescences terminal, or axillary; subumbelliform cymules. Flowers bracteate (each flower subtended by several caducous bracts); regular to somewhat irregular; polycyclic. Free hypanthium absent. Hypogynous disk present; intrastaminal; annular (large, ‘gynophore-like’, wrinkled, denticulate).

Perianth with distinct calyx and corolla; (7–)8(–10); 3 whorled, or 4 whorled (?); isomerous. Calyx 4, or 6; 2 whorled (2+2, rarely 3+3); polysepalous (the innermost larger); not persistent (caducous, leathery); strongly imbricate. Corolla (3–)4(–8); polypetalous; imbricate (the petals unequal, densely streaked with short, resinous lines); white, or yellow; deciduous (caducous). Petals slightly clawed.

Androecium 25–100 (or more). Androecial members maturing centrifugally; free of the perianth; markedly unequal (the outer filaments shorter); irregularly coherent, or free of one another; usually shortly and irregularly connate at the base into groups; 2–4 whorled (in series). Androecium exclusively of fertile stamens. Stamens 25–100 (or more); polystemonous; filantherous. Anthers dehiscing via longitudinal slits; bilocular (the locules widely separated, the connective broad and glandular); tetrasporangiate. Pollen shed as single grains. Pollen grains aperturate; 3–7 aperturate; colporate (colporoidate).

Gynoecium (2–)3(–5) carpelled. The pistil (2–)4(–5) celled. Gynoecium syncarpous; synstylous (Dialyceras, with the carpels free save for a common gynobasic style), or eu-syncarpous (Rhopalocarpus, with a single geniculate style and an entire stigma); superior, or superior to partly inferior (partially sunken in the disk). Carpel of Dialyceras, with free ovaries, 2–9 ovuled. Placentation marginal, or basal. Ovary (2–)4(–5) locular (as many as the carpels, but the ‘locules’ separate in Dialyceras). Gynoecium stylate. Styles 1; from a depression at the top of the ovary; apical, or ‘gynobasic’ (in Dialyceras). Placentation basal to axile (in Rhopalocarpus, but ‘marginal to basal’ in the free locules of Dialyceras). Ovules 2–9 per locule; ascending; anatropous.

Fruit an aggregate, or not an aggregate; indehiscent (Rhopalocarpus), or a schizocarp (Dialyceras). Mericarps in Dialyceras, (2–)3(–5); of Dialyceras with 1(-2) large seeds. Fruit of Rhopalocarpus capsular-indehiscent (globose or lobed according to the number of carpels, densely muricate); 4–10 seeded (1(-2) per locule). Seeds endospermic. Endosperm ruminate; oily. Seeds large. Embryo well differentiated (rather small). Cotyledons 2 (bilobed, sometimes ruminate). Embryo straight.

Physiology, biochemistry. Ellagic acid present.

Geography, cytology. Paleotropical. Tropical. Madagascar.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Malviflorae; Malvales. Cronquist’s Subclass Dilleniidae; Theales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; malvid; Order Malvales.

Species 14. Genera 2; Rhopalocarpus (Sphaerosepalum), Dialyceras.