Circaeasteraceae Kuntze ex Hutch.
Excluding Kingdoniaceae
Habit and leaf form. Small, glabrous herbs. Plants of very peculiar vegetative form; neotenic (the cotyledons persistent, the leaves rosulate-clustered at the tip of the elongated hypocotyl). Annual. Leaves more or less opposite; simple. Lamina obovate (cuneate-spathulate); dichotomously veined; without cross-venules. Leaves exstipulate. Lamina margins apically spinulose dentate.
Leaf anatomy. Stomata present; anomocytic.
Stem anatomy. Nodes unilacunar. Xylem with vessels. Vessel end-walls simple.
Reproductive type, pollination. Fertile flowers hermaphrodite. Plants hermaphrodite. Floral nectaries present (Kingdonia), or absent (Circaeaster). Nectar secretion from the androecium (from the staminodes).
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in fascicles; regular. Free hypanthium absent.
Perianth sepaline; 2(–3); 1 whorled. Calyx 2(–3) (the third member, when present, seemingly representing a reduced stamen); polysepalous; persistent; valvate.
Androecium (1–)2. Androecial members free of the perianth; free of one another. Androecium exclusively of fertile stamens (usually), or including staminodes. Staminodes when present, 1; in the same series as the fertile stamens; sepaloid. Stamens (1–)2; reduced in number relative to the adjacent perianth, or isomerous with the perianth; alternisepalous; erect in bud. Anthers basifixed; non-versatile; dehiscing via longitudinal slits; introrse; bisporangiate. Anther epidermis persistent. Microsporogenesis simultaneous. Anther wall initially with one middle layer; of the ‘dicot’ type. Tapetum glandular. Pollen grains aperturate; 3 aperturate; colpate; 2-celled.
Gynoecium (1–)3 carpelled. Carpels reduced in number relative to the perianth to isomerous with the perianth. The pistil when monomerous, 1 celled. Gynoecium monomerous to apocarpous; of one carpel to eu-apocarpous; superior. Carpel non-stylate (with an oblique, sessile stigma); 1 ovuled. Placentation apical to marginal (subapical). Ovules pendulous; orthotropous; unitegmic; tenuinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 2, or 3; not proliferating. Synergids pear-shaped. Endosperm formation cellular. Embryogeny chenopodiad.
Fruit non-fleshy; not an aggregate (when monomeric), or an aggregate. The fruiting carpel indehiscent; an achene (covered with fine, uncinate setae). Seeds copiously endospermic. Embryo well differentiated. Cotyledons 2 (persistent). Embryo straight.
Physiology, biochemistry. Not cyanogenic.
Geography, cytology. Holarctic. Temperate. Northwest Himalayas to Northwestern China. 2n = 30.
Taxonomy. Subclass Dicotyledonae; dubiously Crassinucelli (despite outstanding features of Tenuinucelli, including corolla absent, stamens free of perianth, initially one middle layer in anther wall, ovules unitegmic and tenuinucellate). Dahlgren’s Superorder Ranunculiflorae; Ranunculales. Cronquist’s Subclass Magnoliidae; Ranunculales. APG (1998) Eudicot; peripheral Eudicot (non-core Eudicots, ‘neither Rosid nor Asterid’); Ranunculales. Species 1. Genera 1; only genus, Circaeaster.
Cite this publication as: ‘L. Watson and M. J. Dallwitz (1992 onwards). The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000. http://biodiversity.uno.edu/delta/’. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000), and Watson and Dallwitz (1991) should also be cited (see References).