SAXIFRAGACEAE (Saxifrage Family)

Plants perennial herbs with rhizomes. Aerial stems sometimes absent, the inflorescence then directly from the rhizome tip. Leaves all or mostly basal, these mostly long-petiolate, those of the apparent flowering stems (actually the inflorescence stalks) either 1 to few, alternate and reduced to scalelike bracts, or a single pair and then conspicuous; these sessile or short-petiolate. Stipules absent or scalelike. Leaf blades simple, the margins entire or more commonly scalloped or toothed. Inflorescences panicles or racemes. Flowers actinomorphic to somewhat zygomorphic, perfect, perigynous. Hypanthium urn-shaped to bell-shaped, partially fused to the ovary. Calyces of 4 or 5 free sepals, these attached along the hypanthium rim. Corollas of 5 free petals, these attached between the sepals along the hypanthium rim. Stamens 5 or 10, the filaments attached just inside the hypanthium rim, the anthers attached at their bases or toward their midpoints. Staminodes absent. Pistil 1 per flower, divided into 2(–4) separate carpels toward the tip, the fused portion 1- or 2-locular. Ovary partially inferior, the hypanthium fused half or more the length of the ovary. Style 1 per free carpel tip, persistent at fruiting. Ovules numerous. Fruits capsules (sometimes appearing as a pair of follicles), the tip of each carpel tapered to a conspicuous stylar beak, dehiscing variously longitudinally. Seeds tiny, often numerous. About 30 genera, about 550 species, North America to South America, Europe, Africa, Asia to New Guinea.

Taxonomic circumscription of the Saxifragaceae is still somewhat controversial. Traditionally (Steyermark, 1963), the family was treated in a relatively broad sense to include about 80 genera and 1,200 total species grouped into 15–17 tribes, but a number of generic groups are now thought to have different affinities. Recent taxonomic and phylogenetic studies (Morgan and Soltis, 1993; Soltis and Soltis, 1997; Bohm et al., 1999) have shown that the woody genera formerly classified in the Saxifragaceae should be segregated into the Grossulariaceae, Hydrangeaceae, and Iteaceae (and several other families not present in Missouri). Two morphologically unusual genera, Parnassia and Penthorum, have been elevated to Parnassiaceae and Penthoraceae, respectively. This dismemberment results in a smaller but morphologically more cohesive Saxifragacaeae and more accurately reflects modern hypotheses of phylogeny in the Saxifragales. See the treatments of the various segregate families for further discussion.

A number of other genera of Saxifragaceae are cultivated as garden ornamentals, but have not escaped into the wild in Missouri, including Astilbe and Tiarella.