Family Diapensiaceae

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. Stomata present; anomocytic, or anomocytic and anisocytic.

Minor leaf veins without phloem transfer cells (Diapensia).

Stem anatomy. Cork cambium present; initially deep-seated, or superficial. Nodes unilacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with vessels. Vessel end-walls simple.

Reproductive type, pollination. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in racemes. The ultimate inflorescence unit 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, biochemistry. 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.
• Technical details: Diapensia.
• Technical details: Pyxidanthera (Lindley).