Saxifragaceae Juss.

Zappi, D. (2009). Neotropical Saxifragaceae.

Morphology

Description

Perennial herbs, often growing together and forming mats. Leaves simple , alternate and basal , rosulate, or rarely opposite, without stipules (stipules sometimes represented by expanded margins of sheathing petiolar leaf bases), entire or deeply lobed to rarely compound , margin often crenate , venation pinnate or often palmate . Inflorescence axillary to terminal , racemose or cymose, bracteate. Flowers showy, hermaphrodite , actinomorphic , rarely zygomorphic , bracteolate; sepals (3-)5, free ; petals (3-)5, often clawed and dissected , white or cream-coloured, rarely pink; stamens 3-10, free , anthers 2-locular; intrastaminal disk present, ovary inferior to superior , 2(-3) carpelate, carpels connate towards base forming a compound , deeply lobed ovary , lobes prolonged into stylar beaks terminated by a capitate stigma , placentation variously axile and parietal , ovules numerous.  Fruit capsular, dry, septicidal or dehiscing along ventral suture of carpels above level of union; seeds numerous, small.

General Description

Notes on delimitation

• In former classifications, the Saxifragaceae used to include not only herbaceous but also woody genera that are nowadays included in other families (Escalloniaceae, Hydrangeaceae, Grossulariaceae). The present circumscription stems from molecular studies that support the Saxifragaceae s.s. (APG II, 2003, Soltis in Smith et al. 2004).

Status

• The few genera present in the Neotropics are associated with highlands, and there are a few cultivated species of Heuchera from Mexico, but this is not expressive in the tropics and does not naturalize. Endemic genera are Tetilla, which occurs only in Chile, and Jepsonia in California reaching Baja California.

Number of genera

Six genera (See Distribution) of which Tetilla is not strictly Neotropical.

Distribution

Distribution in the Neotropics

• In the Neotropics, the Saxifragaceae is quite a marginal family with a few genera occurring at high altitude and reaching Mexico from the West of the USA.
• Heuchera L. - widespread through North America to C. Mexico, 5-6 species.
• Jepsonia Small - endemic to California and Baja California, 2-3 species.
• Saxifraga L. - North temperate regions of the world, in America it occurs in Mexico and in the Andes to Cape Horn and Falkland Islands, 6-7 species.
• Hieronymusiaalchemilloides (Griseb.) Engler - monospecific, formerly placed in Suksdorfia, North America into N. California; Andes of S. Bolivia and NW Argentina.
• Tetillahydrocotylifolia DC. - monospecific, Chile.

Diagnostic

Other important characters

• Intra-staminal nectar disk.
• Carpels projected into stylar beaks terminated by capitatestigma.

Distinguishing characters (always present)

• Perennial herbs.
• Leaves mostly rosulate, margin crenate or lobed.
• Flowers 5-merous, petals clawed and often fimbriate.
• Ovary inferior to superior generally with 2 carpels not fused to the top.
• Fruits capsular with many seeds.

Key differences from similar families

• Vegetatively resembles the Gentianaceae, Apiaceae, Violaceae and other alpine plants found in the Andes, being distinguished from them by its corolla with five distinct petals, stamens 1 or 2 x the number of petals.
• It can be confused with the Crassulaceae, but these are succulent and have carpels totally distinct and generally present in larger number (4 or +).

Literature

Important literature

APG II, 2003. An update of the Angiosperm Phylogeny group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141(4): 399-436.

Soltis, D.E. 2004. Saxifragaceae, pp. 346-348. In: Smith, N., Mori, S.A., Henderson, A., Stevenson, D. and Heald, S.V. (eds.). Flowering Plants of the Neotropics. New York Botanical Garden, Princeton University Press, Princeton.