64f.11. Crataegus Linnaeus (sect. Coccineae) ser. Pruinosae (Sargent) Rehder, Man. Cult. Trees ed. 2. 363. 1940.
Crataegus [unranked] Pruinosae Sargent, Silva 13: 32. 1902
Shrubs or trees, (20–)30–80 dm, main trunk dominant. Stems: trunk bark gray-brown, flattened-scaly, freshly exposed bark often orange-brown; ˂branches spreading; twigs ± straight˃, new growth glabrous, 1-year old usually purple-brown, sometimes tan or reddish brown, 2-years old grayish; thorns on twigs usually numerous, straight to recurved, 2-years old usually black or blackish, shiny, sometimes reddish brown or purple, ± fine to slender or moderately thick, 1.5–5 cm. Leaves: petiole length (28–)50–100% blade, glabrous, usually glandular, sometimes eglandular; blade ˂mid to dark green or ± blue-green˃, ± ovate or ± trullate to rhombic or deltate, sometimes suborbiculate, (2–)3–6(–7) cm, thin to subcoriaceous, base cuneate to truncate, sometimes cordate or rounded, lobes (1–)3 or 4 per side, sinuses shallow to moderately deep, lobe apex ± acute, sometimes ± obtuse, margins finely to coarsely serrate, venation craspedodromous, veins 4–7 per side, apex acute to obtuse, surfaces usually glabrous, sometimes adaxial sparsely hairy young. Inflorescences 4–10-flowered, convex panicles; branches usually glabrous, sometimes sparsely villous; bracteoles caducous, ˂few to numerous, rarely absent˃, linear, membranous, margins sessile- or short-stipitate-glandular. Flowers 15–30 mm diam.; hypanthium glabrous; sepals triangular, length 1/2 petal, margins usually subentire, sometimes entire, rarely glandular-serrate; stamens (10) 20, anthers white to pink or red, sometimes cream; styles 3–5. Pomes pink, mauve, or pale green, sometimes scarlet, deep crimson, or purple, suborbicular, (6–)7–15(–20) mm diam., ˂strongly pruinose˃, glabrous; flesh hard (until overripe); sepals ˂usually on prominent collar˃, spreading, ˂non-accrescent˃; pyrenes (2 or)3–5, ˂often angular˃.
Species 6 (6 in the flora): c, e North America.
Members of ser. Pruinosae are common from Wisconsin through the southern Great Lakes to southern Quebec and southern New England, to Arkansas and Louisiana to Georgia but absent from the southern coastal plain. In the north, they are found mainly in the open; southward they are more often found in woodland shade.
The core of ser. Pruinosae is a natural group of very thorny hawthorns with glabrous, somewhat blue-green, medium-sized to fairly large leaves, mid season anthesis relative to congeners, usually entire sepal margins, and hard, pruinose, often pink or mauve pomes, most with strikingly elevated fruiting calyx. All taxa except Crataegus pruinosa var. dissona have 20 stamens. Crataegus pruinosa var. virella, with the adaxial surface of younger leaves scabrous, might key to ser. Tenuifoliae when in flower. Crataegus gattingeri resembles C. iracunda (ser. Tenuifoliae) in fruit, though differing in leaf adaxial surface indumentum, leaf shape, stamen number, and anther size (see discussion below and under 58. C. iracunda). Members of ser. Pruinosae are similar to members of ser. Intricatae in many particulars, including range; they differ in bracteole form, fruit color, and leaf indumentum and often in stamen number.
The interserial hybrid Crataegus ×coleae keys out in the sixth couplet.
Selected reference Sinnott, Q. P. and J. B. Phipps. 1983. Variation patterns in Crataegus series Pruinosae (Rosaceae) in southern Ontario. Syst. Bot. 8: 59–70.