J. Arnold Arbor. 7: 124. 1926.
Shrubs or trees, 40–60 dm. Stems: twigs: new growth not recorded, 1-year old dark purplish, older gray; thorns on twigs ± straight, 2-years old dark purple, fine, 2–4 cm. Leaves: petiole very slender, 0.5 mm wide, length ca. equal to or 50–66% blade, sparsely hairy or glabrous, slightly glandular or eglandular; blade ovate to deltate-ovate, (2–) 3–4 cm, thin, base broadly rounded to nearly truncate or subcordate, lobes 1–3 per side obscure, sinuses shallow, lobe apex subacute, margins sharply serrate nearly to base, veins 3 per side, apex acuminate, abaxial surface sparsely to ± densely hairy on veins, adaxial variable scabrous, glabrescent. Inflorescences 3–8-flowered; branches glabrous or sparsely villous; bracteoles not recorded. Pedicels glabrous or ± tomentose young. Flowers 15–18 mm diam.; hypanthium not seen; sepal length not recorded, margins glandular-serrate or subentire; stamens 20, anthers pink or rose to rose-purple; styles 3 or 4. Pomes green until late, becoming bright red, obovoid to pyriform, 8–15 mm diam., glabrous; flesh hard; sepals on collar, strongly reflexed; pyrenes 3 or 4.
Crataegus ouachitensis is endemic to the Ouachita Mountains. Among ser. Intricatae, the species is distinct because of its small leaves, only slightly glandular nature, 20 stamens, and bright red pomes. The delicate leaves and pome color recall C. wootoniana (ser. Tenuifoliae). Crataegus ouachitensis is also similar to Louisianan 58. C. iracunda, differing primarily in having 20 stamens and conspicuously glandular-serrate sepal margins in the type form. Crataegus ouachitensis is very rare and likely of interserial hybrid origin, though it could also plausibly be referred to ser. Pulcherrimae. Crataegus thermopegea E. J. Palmer, from the same area, is perhaps related; it has laterally pitted pyrenes and probably ten stamens, according to Palmer.
|1||Petioles 50–66% length of blade; inflorescence branches glabrous; pedicels glabrous; sepal margins glandular-serrate.||Crataegus ouachitensis var. ouachitensis|
|1||Petioles ca. equal to length of blade; inflorescence branches sparsely villous; pedicels ± tomentose young; sepal margins subentire.||Crataegus ouachitensis var. minor|