J. Bot. Res. Inst. Texas 1: 1066, plates 6.2b, 7.2b, fig. 15. 2007.
Shrubs or trees, 20–35 dm, dense and twiggy. Stems: twigs: new growth ± red, glabrous, 1-year old ± glossy, medium to deep brown, 2-years old gray; thorns on twigs numerous, straight to slightly curved, 1-year old deep brown, 2-years old nearly black, slender to ± stout, 2–3.5 cm. Leaves: petiole length 30–40% blade, sessile-glandular, glands 1–few, small, adaxial sulcus pubescent; blade broadly rhombic to broadly elliptic or oblong, length/width = 0.7–1, 2.5–4 cm at anthesis, 3.5–4.5 (–5) cm mature, base cuneate, lobes 2 or 3 per side, max LII 15–25%, lobe apex acute, margins serrulate or crenate-serrate, veins 3 or 4 (or 5) per side, barely impressed, apex acute to subacute, abaxial surface glabrous, adaxial appressed-scabrous (young), often glabrescent. Inflorescences 6–15-flowered; branches glabrate to sparsely pilose; bracteoles pale-brown, very narrow, margins glandular. Flowers 13–16 mm diam.; hypanthium glabrous or sparsely pilose; sepals usually pale green, triangular, 3 mm, abaxial surface glabrous, adaxial pubescent; anthers pink; styles 3 or 4. Pomes deep red to red-burgundy younger, deep purple fully ripe, ellipsoid to suborbicular, (9–) 11–12 mm, glabrous; sepals eroded or spreading, 4–4.5 mm, pointed; pyrenes 3 or 4, dorsally shallowly or more deeply grooved, sides longitudinally grooved or very shallowly concave.
Phenology: Flowering late May–early Jun; fruiting Aug–Sep.
Habitat: Thickets, light shade of aspen
Elevation: 800–1100 m
Crataegus purpurella is known only from the eastern half of the Cypress Hills; it is common in thickets along north-slope draws. The species is most similar to C. rivulopugnensis, with which it is allopatric. In the open, it is a much denser shrub than C. rivulopugnensis; both have short, slender thorns. Crataegus purpurella also differs from C. rivulopugnensis in its usually smaller, proportionately wider, fewer veined leaves and in the deep purple, rather than red, fruit at maturity.