Family Crossosomataceae

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. Stomata present; anomocytic.

Lamina isobilateral. The mesophyll containing calcium oxalate crystals. The mesophyll crystals raphides (minute, yellow).

Stem anatomy. Cork cambium present; initially superficial. Nodes unilacunar, or tri-lacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with tracheids; with vessels. Vessel end-walls horizontal; simple. Wood parenchyma mostly apotracheal.

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

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.
• Technical details: Crossosoma.
• Crossosoma: Chittenden.