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The families of flowering plants

L. Watson and M.J. Dallwitz

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; petiolate; simple. Lamina entire; obovate (cuneate-spathulate); dichotomously veined, cf. Kingdonia; without cross-venules; attenuate at the base. Leaves exstipulate. Lamina margins apically spinulose dentate.

Leaf anatomy. Stomata present; mainly confined to one surface (abaxial); small, anomocytic. Midrib conspicuous. Main veins embedded.

Axial (stem, wood) anatomy. Nodes unilacunar. Primary vascular tissues diarch; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening almost absent, or developing from a conventional cambial ring (if detectable, slight, with only a small amount of secondary xylem and phloem at either side).

The vessel end-walls simple.

Reproductive type, pollination. Fertile flowers hermaphrodite. Plants hermaphrodite. Floral nectaries absent.

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, phytochemistry. Not cyanogenic.

Geography, cytology. Holarctic. Temperate. Northwest Himalayas to Northwestern China. 2n = 30.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Ranunculiflorae; Ranunculales. Cronquist’s Subclass Magnoliidae; Ranunculales. APG 3 core angiosperms; peripheral eudicot; Superorder Ranunculanae; Order Ranunculales.

Species 1. Genera 1; only genus, Circaeaster.

General remarks. Continued assignment of this to Ranunculales (Crassinucelli) seems remarkable, in the face of morphological and embryological features characteristic of Tenuinucelli: corolla absent, initially one middle layer in the anther wall, ovules unitegmic and tenuinucellate.

Illustrations. • Technical details: Circaeaster (Hutchinson).

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: 13th March 2017.’.