The families of flowering plants.
Habit and leaf form. Erect, branched herbs.Plants non-succulent. Annual, or biennial (sometimes glandular); with neither basal nor terminal aggregations of leaves. Leaves opposite;not gland-dotted; simple. Lamina entire; linear to lanceolate, or ovate; attenuate at the base. Leaves exstipulate. Lamina margins entire.
Leaf anatomy. Lamina isobilateral, or centric.
Stem anatomy. Cork cambium present; initially superficial (in the epidermis). Cortical bundles absent. Medullary bundles absent. Internal phloem absent.
Reproductive type, pollination. Fertile flowershermaphrodite. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes. The ultimate inflorescence unit cymose. Inflorescences terminal and axillary; sympodial, cymose, the flowers paired. Flowers regular; 5 merous; cyclic; tetracyclic. Free hypanthium absent.
Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous; regular; valvate. Corolla 5; 1 whorled; polypetalous (the petals shorter than the sepals); imbricate; regular; white, or yellow. Petals ovate-spathulate.
Androecium 5. Androecial members free of the perianth (inserted on the margin of the epigynous disk); all equal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5; isomerous with the perianth; oppositisepalous; alternating with the corolla members; filantherous (the filaments subulate). Anthers dorsifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral. Tapetum glandular (?, the cells becoming binucleate). Pollen grains 2-celled.
Gynoecium 2–3 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous; synovarious; inferior.Ovary 1 locular. Epigynous disk present (inconspicuous). Gynoecium stylate. Styles 2–3 (thick, divaricate); free; apical. Stigmas 2–3; dorsal to the carpels (according to Hutchinson); capitate. Placentation apical (with 2–3 remarkably large, pendulous, apical placentas). Ovules in the single cavity 50–200 (‘very numerous’); pendulous; anatropous; bitegmic; tenuinucellate. Outer integument not contributing to the micropyle. Endothelium differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; persistent. Synergids hooked. Endosperm formation cellular. Endosperm haustoria present; chalazal. Embryogeny caryophyllad.
Fruit non-fleshy; dehiscent; a capsule. Capsules apically 2–3 valvular. Fruit 50–200 seeded (‘very numerous’). Seeds minute; appendaged.
Physiology, biochemistry. Iridoids detected (S.R. Jensen, unpublished); ‘Route I’ type.
Geography, cytology. Paleotropical and Cape. Temperate to tropical. Tropical and South Africa to Northwest India.
Taxonomy.Subclass Dicotyledonae; Tenuinucelli (polypetalous, but iridoids present and ovules tenuinucellate). Dahlgren’s Superorder Rosiflorae; Saxifragales. Cronquist’s Subclass Rosidae; Rosales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order unassigned to Order.
Species 5. Genera 1; only genus, Bistella (Vahlia).