The families of flowering plants

L. Watson and M.J. Dallwitz

Crossosomataceae Endl.

Habit and leaf form. Glabrous, sometimes spinescent shrubs. Xerophytic. Leaves deciduous; small; alternate, or opposite (Apacheria); simple. Lamina entire; pinnately veined; cross-venulate. Leaves minutely stipulate, or exstipulate. Lamina margins apically tri- dentate, or entire.

Leaf anatomy. The leaf lamina bifacial. Stomata present; anomocytic. The mesophyll containing crystals. The crystals raphides (minute, yellow).

Axial (stem, wood) anatomy. Young stems with solid internodes, or with hollow internodes. Pith homogeneous (comprising abundantly pitted parenchymatous cells). Cork cambium present; initially superficial. Nodes unilacunar, or tri-lacunar. 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. The vessels clustered, or in tangential arcs. The vessel end-walls horizontal; simple. The axial xylem with tracheids (vasicentric). The parenchyma mostly scanty apotracheal. ‘Included’ phloem absent. The wood not storied.

Reproductive type, pollination. Plants hermaphrodite, or andromonoecious, or gynomonoecious, or polygamomonoecious (?).

Inflorescence, floral, fruit and seed morphology. Flowers solitary; terminal, or axillary; medium-sized; regular; cyclic; polycyclic. Free hypanthium present (short). Hypogynous disk present; extrastaminal to intrastaminal; annular.

Perianth with distinct calyx and corolla; (6–)8, or 10(–12); 2 whorled; isomerous. Calyx (3–)4–5(–6); 1 whorled; polysepalous; regular; persistent; imbricate. Corolla (3–)4–5(–6); 1 whorled; polypetalous; imbricate; regular; white; plain; deciduous. Petals clawed (spathulate or orbicular); entire.

Androecium 20–50(–100) (‘many’). Androecial members branched (associated with trunk bundles); maturing centripetally, or maturing centrifugally (? — conflicting reports from Eames 1953, Thorne 1978); free of the perianth (on the hypanthium); free of one another; 1 whorled (by suppression of the antepetalous cycle), or 2 whorled, or 3–4 whorled. Androecium exclusively of fertile stamens. Stamens 20–50(–100) (‘many’); polystemonous; filantherous (the filaments slender). Anthers basifixed (to slightly ventrifixed); versatile; dehiscing via longitudinal slits; extrorse to latrorse (slightly extrorse); tetrasporangiate. Pollen grains aperturate; (2–)3 aperturate; colporate; 2-celled.

Gynoecium 1–5(–9) carpelled. Carpels reduced in number relative to the perianth, or isomerous with the perianth, or increased in number relative to the perianth. The pistil when monomerous, 1–5(–9) celled. Gynoecium monomerous, or apocarpous; of one carpel, or eu-apocarpous; superior. Carpel stylate (the style short, stout); apically stigmatic (the stigma terminal and expanded, or vertically decurrent on the style); (1–)2–100 ovuled (to ‘many’). Placentation marginal. Ovules arillate; campylotropous, or amphitropous; bitegmic; crassinucellate. Endosperm formation nuclear (?).

Fruit non-fleshy; an aggregate (when apocarpous), or not an aggregate (when monomeric). The fruiting carpel dehiscent; a follicle. Seeds thinly to copiously endospermic. Endosperm oily. Embryo well differentiated. Cotyledons 2.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. Anatomy ‘Kranz’, according to Cronquist 1981!. Not cyanogenic. Iridoids not detected. Saponins/sapogenins absent. Proanthocyanidins present, or absent. Ellagic acid present.

Geography, cytology. Neotropical. Temperate to sub-tropical. Arid Southwest U.S.A. and Mexico.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rosiflorae; Rosales. Cronquist’s Subclass Rosidae; Rosales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; malvid; Order Crossosomatales.

Species 8–10. Genera 3; Apacheria, Crossosoma, Glossopetalon (Forsellesia).

Illustrations. • Crososoma californicum: Bot. Mag. 130 (1904). • Le Maout and Decaisne: Crossosoma. • Crossosoma californicum: Chittenden.

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: 24th October 2017.’.