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The families of flowering plants

L. Watson and M.J. Dallwitz

Saxifragaceae Juss.

Including Bicornaceae Dulac; excluding Eremosynaceae, Escalloniaceae, Francoaceae, Grossulariaceae, Lepuropetalaceae, Parnassiaceae, Penthoraceae, Vahliaceae.

Habit and leaf form. Herbs. Plants succulent (somewhat, sometimes), or non-succulent. Annual, or perennial; with a basal aggregation of leaves, or without conspicuous aggregations of leaves. Mesophytic, or xerophytic (many being arctic/alpine). Leaves small, or medium-sized; alternate (nearly always), or opposite (sometimes); usually spiral; ‘herbaceous’, or fleshy (occasionally); petiolate to sessile; sheathing, or non-sheathing. Leaf sheaths not tubular; with free margins. Leaves not gland-dotted; simple, or compound (e.g., Astilbe, Rodgersia); when compound,, ternate, or palmate (usually 3 or 5 foliolate). Lamina when simple, dissected, or entire; when incised, pinnatifid; one-veined, or pinnately veined, or palmately veined; cross-venulate. Leaves exstipulate. Lamina margins entire, or crenate, or serrate, or dentate. Leaf development not ‘graminaceous’.

Leaf anatomy. The leaf lamina dorsiventral, or bifacial, or centric. Hydathodes commonly present. Stomata present; mainly confined to one surface, or on both surfaces; usually anomocytic. Hairs of various forms present; eglandular and glandular. The mesophyll containing crystals (rarely), or without crystals. The crystals when present, druses. Minor leaf veins without phloem transfer cells (Chrysosplenium, Saxifraga, Tiarella).

Axial (stem, wood) anatomy. Secretory cavities absent. Cork cambium present; initially superficial. Nodes tri-lacunar (usually), or multilacunar (e.g. Astilbe). Primary vascular tissues in a cylinder, without separate bundles, or comprising a ring of bundles; collateral. Cortical bundles present, or absent. Medullary bundles present, or absent. Secondary thickening absent, or developing from a conventional cambial ring.

The vessel end-walls simple.

Reproductive type, pollination. Plants hermaphrodite. Floral nectaries usually present. Nectar secretion from the disk. Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary (rarely), or aggregated in ‘inflorescences’; in cymes, or in racemes, or in spikes, or in heads, or in fascicles, or in panicles. The ultimate inflorescence units cymose, or racemose. Inflorescences scapiflorous, or not scapiflorous; various. Flowers small, or medium-sized; regular, or somewhat irregular to very irregular. The floral irregularity when irregular, involving the perianth (the petals dimorphous). Flowers 5 merous; cyclic; pentacyclic (usually), or tetracyclic. Floral receptacle (when flower hypogynous) markedly hollowed to not markedly hollowed. Free hypanthium present, or absent. Hypogynous disk present (usually), or absent; when present, intrastaminal.

Perianth with distinct calyx and corolla (usually), or sepaline (corolla sometimes lacking); usually 10; usually 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous, or gamosepalous; regular; imbricate, or valvate; with the median member posterior. Corolla 5; 1 whorled; polypetalous, or gamopetalous; imbricate, or valvate; regular; white, or yellow, or red, or pink (not blue). Petals clawed (often), or sessile.

Androecium 10 (usually), or 5. Androecial members free of the perianth; all equal, or markedly unequal; free of one another; 2 whorled. Androecium exclusively of fertile stamens. Stamens 10 (usually), or 5; diplostemonous (usually), or isomerous with the perianth; usually alternisepalous (obdiplostemonous). Anthers cohering (in pairs), or separate from one another; basifixed (mostly), or dorsifixed (slightly only, e.g. Heuchera, Bergenia); versatile; dehiscing via longitudinal slits; slightly introrse, or latrorse (e.g. Saxifraga), or extrorse and introrse (Tolmiea, with the median extrorse and the laterals introrse); tetrasporangiate. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Anther wall initially with one middle layer, or initially with more than one middle layer (1 or 2). Tapetum glandular. Pollen grains aperturate; 3(–5) aperturate; colporate (or colporoidate); 2-celled (in Astilbe, Bergenia, Heuchera and Saxifraga).

Gynoecium 2(–5) carpelled. Carpels reduced in number relative to the perianth (usually), or isomerous with the perianth (when carpels more or less free). The pistil 2(–3) celled. Gynoecium apocarpous to syncarpous; semicarpous to synovarious (i.e. carpels more or less joined below); superior to inferior. Ovary 2(–3) locular. Gynoecium when G2 (i.e. usually), median. Styles 2(–3); free; apical; shorter than the ovary. Stigmas dorsal to the carpels; wet type, or dry type; papillate; Group II type, or Group III type. Placentation axile. Ovules 9–30 per locule (in several rows); pendulous, or ascending; anatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; proliferating (rarely, to 5 cells), or not proliferating; ephemeral, or persistent. Synergids hooked (and usually with filiform apparatus). Endosperm formation cellular, or helobial. Embryogeny solanad.

Fruit non-fleshy; an aggregate (rarely), or not an aggregate; dehiscent; a capsule. Capsules usually septicidal. Fruit 20–50 seeded (‘very numerous’). Seeds endospermic. Endosperm oily. Seeds minute to small. Cotyledons 2. Embryo achlorophyllous (3/4); straight. Micropyle zigzag, or not zigzag.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3 and CAM (?). C3 physiology recorded directly in Heuchera. Anatomy non-C4 type (Heuchera). Cyanogenic, or not cyanogenic. Arbutin present, or absent (?). Iridoids not detected. Proanthocyanidins present, or absent; when present, cyanidin, or cyanidin and delphinidin. Flavonols present; quercetin, or kaempferol and quercetin, or kaempferol, quercetin, and myricetin. Ellagic acid present (Bergenia), or absent (4 species, 4 genera). Aluminium accumulation demonstrated, or not found (usually?). Sieve-tube plastids S-type.

Geography, cytology. Frigid zone to temperate. Chiefly North temperate, a few Southern temperate and tropical mountains.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rosiflorae; Saxifragales. Cronquist’s Subclass Rosidae; Rosales. APG 3 core angiosperms; core eudicot; unplaced at Superordinal level; Order Saxifragales.

Species 580. Genera about 30; Astilbe, Astilboides, Bensoniella, Bergenia, Bolandra, Boykinia, Chrysosplenium, Conimitella, Darmera (Peltiphyllum), Elmera, Heuchera, Jepsonia, Leptarrhena, Lithophragma, Mitella, Mukdenia, Oresitrophe, Rodgersia, Saxifraga, Saxifragella, Saxifragodes, Saxifragopsis, Suksdorfia, Sullivantia, Tanakaea, Tellima, Tiarella, Tolmiea.

Illustrations. • Technical details: Saxifraga. • Astilbe rivularis: as Spiraea barbata, Bot. Reg. 2011, 1837. • Bergenia ciliata: Bot. Reg. 29 (65), 1843. • Heuchera cylindrica: as H. cylindracea, Bot. Reg. 1924, 1837. • Rodgersia podophylla: Bot. Mag. 109 (1883). • Saxifraga aretioides: Bot. Mag. 96 (1870). • Saxifraga species (B. Ent. compilation). • Saxifraga species, Chrysosplenium (B. Ent. compilation. • Saxifraga granulata: Eng. Bot. 555 (1865). • Saxifraga hirsuta: as S. geum, Eng. Bot. 455 (1865). • Saxifraga stellaris: Eng. Bot. 542 (1865). • Saxifraga umbrosa: Eng. Bot. 547 (1865).

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: 30th September 2017.’.