w United States, Mexico.
Genera 4, species ca. 8 (3 genera, 7 species in the flora).
For years, Crossosomataceae were thought to comprise only the type genus. In 1975, the circumscription was expanded with the discovery of Apacheria, and three years later it was enlarged further with the transfer of Glossopetalon from the Celastraceae (R. F. Thorne and R. Scoggin 1978). A fourth genus, the monospecific Velascoa Calderón & Rzedowski, endemic to northeastern Querétaro, Mexico, was described in 1997. Velascoa recondita Calderón & Rzedowski is unique in the family in its elongate, narrowly funnelform hypanthium and nearly sessile stamens.
The affinities of the family have been controversial. A. Cronquist (1981) outlined the problems, noting that the presence of an aril (and some embryologic features) suggested a placement in the Dilleniales, but he chose instead to classify the family tentatively in his concept of Rosales, near the Rosaceae, based on superficial floral similarities such as perigyny. V. Sosa and M. W. Chase (2003), who studied DNA sequence variation, and M. L. Matthews and P. K. Endress (2005), who studied developmental floral morphology, independently concluded that the Crossosomatales should be segregated as a distinct order (including such morphologically diverse families as Stachyuraceae and Staphyleaceae). The circumscription and placement of this order in relation to other Rosids are still uncertain.
|1||Stamens 15–50; sepals and petals 5; petals 9–18 mm; follicles finely transversely verrucose or indistinctly reticulate; seeds 4–22 per follicle; aril deeply fimbriate.||Crossosoma|
|1||Stamens 8 or 4–10; sepals and petals 4 or 3–5(–6); petals 4–5 mm or 2–9 mm; follicles longitudinally striate; seeds 1 or 2 per follicle; aril irregularly discoid or ± fimbrillate||> 2|
|2||Leaves opposite, sometimes appearing fasciculate on short shoots, blade margins entire or apically 2–3-lobed; stigmas linear; sepals and petals 4.||Apacheria|
|2||Leaves alternate, blade margins entire; stigmas capitate, oblique; sepals and petals 3–5(–6).||Glossopetalon|