21. Crataegus pruinosa (H.L. Wendl.) K. Koch (frosted hawthorn)

C. aperta Sarg.

C. aspera Sarg.

C. brachypoda Sarg.

C. bracteata Sarg.

C. calliantha Sarg.

C. decorata Sarg.

C. disjuncta Sarg.

C. dissona Sarg.

C. eggertii Britton

C. leiophylla Sarg.

C. mackenzii Sarg.

C. mackenzii var. aspera (Sarg.) E.J. Palmer

C. magnifolia Sarg.

C. patrum Sarg.

C. platycarpa Sarg.

C. rigida Sarg.

C. rubicundula Sarg.

C. rugosa Ashe

C. seclusa Sarg

C. seducta Sarg.

C. tumida Sarg.

C. virella Ashe

Mespilus pruinosa H.L. Wendl.

Pl. 529 a–f, h, i; Map 2432

Plants shrubs, 2–4 m tall. Twigs reddish-brown when young, dull purple-brown at end of first year, becoming dull gray at second year, paler gray with age, glabrous .Thorns on branchlets mostly 3–5 cm long, purplish brown to black at second year. Petioles 15–30 mm long, very slender, glabrous, nonglandular or with a few, inconspicious, sessile, dark glands. Leaf blades 2.5–6.0 cm long, often relatively broad (to 90% as wide as long) and broadly angled to rounded, truncate, or shallowly cordate at the base or, if relatively narrow, then rounded to angled at the base, ovate to broadly ovate or triangular-ovate, usually with 3 or 4 shallow to moderate (at most 30% of the way to the midvein), sharp lobes per side (except in var. magnifolia, with has some or most of the leaves unlobed or merely with short to obscure and often blunt or rounded lobes), mostly with 4–6 pairs of secondary veins per side, the upper surface glabrous or less commonly sparsely to densely roughened-hairy when young (then often becoming glabrous or nearly so at maturity), the undersurface glabrous or occasionally sparsely to moderately soft-hairy along the veins when young (then often becoming glabrous or nearly so at maturity). Inflorescences mostly 5–10-flowered; the branches glabrous or rarely sparsely hairy. Flowers 15–22 mm in diameter. Sepals 4–5(–7) mm long, the lobes triangular to narrowly triangular or linear above a triangular base. Stamens (10–)20, the anthers 0.7–1.0 mm long, ivory to cream-colored or pale to bright pink, rarely dull purple. Styles 3–5. Fruits 9–16 mm in diameter, reddish pink to red or green with pink to purple areas, often strongly glaucous. Nutlets 2–5. 2n=51, 68, 72; triploid (by anatomical sections; see Longley [1924]); triploid to tetraploid (by flow cytometry; see Talent and Dickinson [2005]). Mid-April–late May.

Scattered nearly throughout the state (eastern U.S. west to Iowa, Kansas, and Oklahoma; southeastern Canada). Mesic to dry upland forests, banks of streams and rivers, glades, bases and ledges of bluffs, and occasionally bottomland forests; also pastures, old fields, fence rows, and roadsides.

Frosted hawthorn is a widespread species and very variable in leaf morphology. It is characterized (except for uncommon forms) in being glabrous and having strongly glaucous (pruinose) fruits, at least the immature ones, hence the vernacular name. There are several more or less well-marked varieties of C. pruinosa in Missouri, as well as a large array of less distinctive forms. The major variants may be distinguished using the following key. Plants with 10 stamens (var. dissona) usually have pink anthers, but occasionally they produce pale, cream-colored anthers. Distinctive plants with relatively small, moderately to densely hairy leaves may be referred to as C. pruinosa var. virella. However, sparsely hairy plants are occasionally encountered and have been called C. mackenzii and C. decorata in the older literature. These differ somewhat in leaf shape from var. virella and thus are better considered unusual components of var. pruinosa. Crataegus aspera is a poorly understood taxon based on a few historical specimens from Jasper County. It has strongly roughened-hairy foliage and inflorescences, as well as somewhat larger leaves than is typical in var. virella. Plausibly it may reflect past hybridization between C. pruinosa and C. biltmoreana (ser. Intricatae). If future studies find that this taxon should be combined with var. virella, then the epithet aspera has priority at the varietal rank and a new combination will have to be published under C. pruinosa.