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The families of flowering plants

L. Watson and M. J. Dallwitz

Diapensiaceae Lindl.

Including Diplarchaceae Klotsch, Galacinae (Galacaceae) D. Don

Habit and leaf form. Small shrubs, or herbs. Plants autotrophic. Perennial. Leaves evergreen; small, or medium-sized; alternate; spiral; imbricate, or not imbricate; petiolate to sessile; non-sheathing; simple. Lamina entire; one-veined, or pinnately veined; often cross-venulate. Leaves exstipulate. Lamina margins entire, or serrate, or dentate. Vernation not circinnate.

Leaf anatomy. The leaf lamina dorsiventral (usually, but “the mesophyll sometimes consisting of isodiametric cells” in Galax and Shortia). Stomata present; mainly confined to one surface (usually the abaxial one, sometimes the adaxial), or on both surfaces; anomocytic, or anomocytic and anisocytic (in Galax and Shortia). Hairs very scarce or absent, or present (and conspicuous, only in Pyxidanthera); in Pyxidanthera, exclusively eglandular; unicellular. Complex hairs absent. Lamina without secretory cavities. The mesophyll containing crystals. The crystals druses (mostly), or raphides (in Galax). Minor leaf veins without phloem transfer cells (Diapensia).

Axial (stem, wood) anatomy. Pith often heterogeneous. Cork cambium present (but sometimes scarcely developed); initially deep-seated (usually?), or initially superficial (in Galax). Nodes unilacunar. Primary vascular tissues in a cylinder, without separate bundles; collateral. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays narrow.

The wood ring porous to diffuse porous. The vessel end-walls simple, or scalariform and simple. The axial xylem with fibre tracheids; with libriform fibres (in addition to fibre tracheids), or without libriform fibres. ‘Included’ phloem absent. The wood not storied.

Reproductive type, pollination. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in racemes. The ultimate inflorescence units racemose. Flowers bracteolate (with two bracteoles); small, or medium-sized; regular; 5 merous; cyclic; tetracyclic, or pentacyclic. Free hypanthium absent. Hypogynous disk absent.

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous, or gamosepalous; when gamosepalous, five blunt-lobed; regular; persistent; imbricate. Corolla 5; 1 whorled; polypetalous (Galax), or gamopetalous; imbricate, or contorted; regular; white, or pink, or purple (anthocyanic); deciduous. Petals deeply bifid, or bilobed, or fringed, or entire.

Androecium 5, or 10. Androecial members (at least the outer series) adnate (to the corolla tube); all equal, or markedly unequal (when staminodes present); free of one another to coherent (then the stamens, or those of the inner cycle, or the staminodes and stamens together connivent basally to form an androecial tube, which in Galax falls with the corolla); 1 adelphous; 1 whorled (Diapensia, Pyxidanthera), or 2 whorled. Androecium exclusively of fertile stamens (Diapensia, Pyxidanthera), or including staminodes. Staminodes when present, 5; in the same series as the fertile stamens, or internal to the fertile stamens (?—antepetalous); non-petaloid (scalelike or spathulate). Stamens 5, or 10; isomerous with the perianth (usually), or diplostemonous; oppositisepalous; alternating with the corolla members, or both alternating with and opposite the corolla members; filantherous, or with sessile anthers. Anthers basifixed (or transverse); becoming inverted during development, their morphological bases ostensibly apical in the mature stamens; non-versatile; dehiscing via longitudinal slits (usually), or dehiscing transversely (Pyxidanthera); unilocular (Galax), or bilocular; bisporangiate (Galax), or tetrasporangiate; appendaged (awned), or unappendaged. The anther appendages when present, basal. Endothecium developing fibrous thickenings. Anther epidermis persistent. Anther wall initially with more than one middle layer. Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate, or 6 aperturate; colpate, or colporate, or rugate; 2-celled.

Gynoecium 3 carpelled. Carpels reduced in number relative to the perianth. The pistil 3 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 3 locular; sessile. Gynoecium stylate. Styles 1; attenuate from the ovary; apical. Stylar canal present. Stigmas 1; 3 lobed; capitate; wet type; non-papillate; Group IV type. Placentation axile. Ovules 5–50 per locule (‘many’); funicled; hemianatropous, or anatropous, or campylotropous; unitegmic; tenuinucellate. Endothelium differentiated, or not differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; proliferating (to 40 cells, in Shortia), or not proliferating; persistent. Synergids of Diapensia with filiform apparatus. Endosperm formation cellular. Embryogeny probably solanad.

Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Seeds copiously endospermic; small. Embryo well differentiated. Cotyledons 2. Embryo straight to curved.

Physiology, phytochemistry. Not cyanogenic. Alkaloids absent (one species). Iridoids not detected. Proanthocyanidins absent. Flavonols present; quercetin, or kaempferol and quercetin (and sometimes with gossypetin). Ellagic acid absent (Galax). Ursolic acid absent. Aluminium accumulation widely demonstrated (seemingly occurring in all the species).

Geography, cytology. Holarctic. Frigid zone to temperate. North America and Eurasia - chiefly alpine. X = 6.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Corniflorae; Ericales. Cronquist’s Subclass Dilleniidae; Diapensiales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; Order Ericales.

Species 20. Genera 6; Berneuxia, Diapensia, Galax, Pyxidanthera, Schizocodon, Shortia.

Illustrations. • Diapensia lapponica: Bot. Mag. 27 (1808). • Technical details: Diapensia. • Technical details: Pyxidanthera (Lindley).

The descriptions are offered for casual browsing only. We strongly advise against extracting comparative information from them. This is much more easily achieved using 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).

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 22nd August 2016.’.