Habit and leaf form. Small trees, or shrubs. Autotrophic. Leaves evergreen, or deciduous; alternate; `herbaceous', or leathery; petiolate to sessile; simple. Lamina entire; pinnately veined; cross-venulate. Leaves exstipulate (but with red, ligulate, glandular structures in the leaf axils). Lamina margins entire.
Leaf anatomy. Mucilaginous epidermis present, or absent. Stomata present; mainly confined to one surface (abaxial); anomocytic.
Lamina dorsiventral. The mesophyll containing calcium oxalate crystals. The mesophyll crystals druses, or druses and solitary-prismatic.
Stem anatomy. Cork cambium present; initially deep-seated. Nodes unilacunar. Secondary thickening developing from a conventional cambial ring. Xylem with tracheids, or without tracheids; with fibre tracheids; with vessels. Vessel end-walls oblique; scalariform. Wood ring porous; parenchyma apotracheal, or apotracheal and paratracheal.
Root anatomy. Root xylem with vessels.
Reproductive type, pollination. Hermaphrodite. Floral nectaries present. Nectar secretion from the perianth (from the petals, in Cyrilla), or from the disk, or from the perianth and from the disk (?).
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in `inflorescences'; in racemes. The terminal inflorescence unit racemose. Inflorescences terminal, or axillary. Flowers bracteate (the bract sometimes caducous); bracteolate; fragrant; regular; 5(-7) merous; cyclic; tetracyclic, or pentacyclic. Free hypanthium absent. Hypogynous disk present; intrastaminal.
Perianth with distinct calyx and corolla; 10(-14); 2 whorled; isomerous. Calyx 5(-7); 1 whorled; polysepalous, or gamosepalous (connate basally); regular; persistent; accrescent (often), or non-accrescent; imbricate. Corolla 5(-7); 1 whorled; polypetalous, or gamopetalous (then shortly so at the base); imbricate, or contorted; white, or red, or pink, or purple.
Androecium 5 (Cyrilla), or 10. Androecial members free of the perianth; all equal, or markedly unequal (those of the outer whorl longer, in Cliftonia); free of one another; 1 - whorled (Cyrilla), or 2 - whorled (5+5). Androecium exclusively of fertile stamens. Stamens 5 (representing the outer whorl, in Cyrilla), or 10; isomerous with the perianth (Cyrilla), or diplostemonous; oppositisepalous (alternating with the petals); erect in bud (Purdiaea), or inflexed in bud; filantherous (the filaments sometimes flattened and petaloid). Anthers dorsifixed; becoming inverted during development, their morphological bases ostensibly apical in the mature stamens (in Purdiaea), or not becoming inverted during development (in the other genera - the filaments attached dorsally in Cyrilla and Cliftonia, but ventrally in Purdiaea); versatile; dehiscing via pores (these apical, in Purdiaea), or dehiscing via short slits, or dehiscing via longitudinal slits; introrse; tetrasporangiate. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Anther wall initially with more than one middle layer (2 or 3). Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate; 3(-4) - aperturate; colporate; 2-celled.
Gynoecium 2-5. Carpels reduced in number relative to the perianth to isomerous with the perianth. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 2-5 locular. Gynoecium shortly non-stylate, or stylate. Styles when detectable, 1; attenuate from the ovary; apical. Stigmas dry type; non-papillate; Group IV type. Placentation axile to apical. Ovules 1-3 per locule; pendulous (sometimes from a pendulous, stalklike placenta); orthotropous (Purdiaea), or anatropous (Thomas 1960); unitegmic; tenuinucellate. Endothelium differentiated. Embryo-sac development Polygonum-type (from normal embryo sacs, but Hieracium-type from the aposporous embryo sacs in Cliftonia). Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating. Endosperm formation cellular. Endosperm haustoria present; chalazal and micropylar.
Fruit fleshy, or non-fleshy; indehiscent; capsular-indehiscent, or a samara, or a drupe. Seeds copiously endospermic; without a testa. Embryo well differentiated. Cotyledons 2 (small). Embryo straight.
Physiology, biochemistry. Not cyanogenic. Alkaloids absent (3 species). Iridoids absent. Proanthocyanidins present; cyanidin. Flavonols present; kaempferol, quercetin, and myricetin. Ellagic acid faintly present (Cyrilla). Aluminium accumulation not found.
Peculiar feature. Non-mangrove species.
Geography, cytology. Neotropical. Sub-tropical to tropical. Southeast U.S.A., Central and tropical South America. X = 10.
Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren's Superorder Corniflorae; Ericales. Cronquist's Subclass Dilleniidae; Ericales. Takhtajan's Subclass Dilleniidae; Ericanae; Ericales. Species 13. Genera 3; Cliftonia, Cyrilla, Purdiaea.
Thomas 1960.
Economic uses, etc. Leatherwood (Cyrilla) and `buckwheat tree' (Cliftonia) are cultivated for fragrant flowers and showy autumn foliage.
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