12. Crataegus calpodendron (Ehrh.) Medik. (late hawthorn)

C. calpodendron var. globosa (Sarg.) E.J. Palmer

C. calpodendron var. hispidula (Sarg.) E.J. Palmer

C. calpodendron var. microcarpa (Chapm.) E.J. Palmer

C. calpodendron var. mollicula (Sarg.) E.J. Palmer

C. globosa Sarg.

C hispidula Sarg.

C. insperata Sarg.

C. mollicula Sarg.

C. mollita Sarg.

C. obesa Ashe

C. obscura Sarg.

C. scabera Sarg.

C. spinulosa Sarg.

C. tomentosa L. var. microcarpa Chapm.

Mespilus calpodendron Ehrh.

Pl. 527 a–f; Map 2423

Plants shrubs or more commonly small trees, 4–7 m tall, the trunks variously unarmed to relatively densely thorny. Branchlets often unarmed or nearly so, occasionally sparsely thorny, the thorns mostly 2.5–6.0 cm long. Twigs dark brown and shiny at second year, densely pubescent (at least along rapidly growing shoots) with soft, fine, often somewhat tangled, yellowish brown hairs when young, becoming less hairy at second year, eventually glabrous with age. Petioles 10–30 mm long, narrowly winged for most of the length, finely hairy, sometimes only on the upper side. Leaf blades 3–12 cm long, ovate to oblong-elliptic or rhombic, rarely nearly circular, with (2–)5–8 shallow lobes per side, rarely unlobed, the upper surface green to yellowish green, roughened-hairy when young, becoming glabrous or nearly so at maturity, the undersurface usually persistently pubescent with soft, more or less appressed hairs, especially on the veins, the veins not conspicuously impressed on the upper surface. Inflorescences 12–25(–45)-flowered, the branches densely hairy. Flowers 13–15(–22) mm in diameter. Stamens (10–)20, the anthers pink, red, or pinkish purple, occasionally ivory. Fruits (5–)7–9(–10) mm in diameter, oblong-ellipsoid to less commonly globose, orangish red to red. 2n=34, 56, 68; diploid or triploid (by flow cytometry; see Talent and Dickinson [2005]). Late April–mid-June.

Scattered nearly throughout the state, but apparently uncommon or absent from many of the westernmost counties (eastern U.S. west to Wisconsin and Texas; southeastern Canada). Mesic to dry upland forests, savannas, glades, bases, ledges, and tops of bluffs, banks of streams and rivers, edges of marshes, and bottomland forests; also fence rows and roadsides.

This is a widespread and usually distinctive species. It is one of the latest of the native hawthorns to begin flowering (only C. phenopyrum is sometimes later) in all parts of its range. Several varieties have been recognized in C. calpodendron, most of which, if accepted, can be found in Missouri. These have been said to differ in degree of leaf lobing, density of pubescence, prominence of venation, and slight differences in fruit shape. In general those forms with narrower, more elliptic, less deeply lobed leaves have shorter and somewhat blunter leaf-teeth, whereas forms with more nearly isodiametric leaves have the deepest and sharpest lobes as well as the biggest and sharpest marginal teeth. The number of lateral veins increases with narrowness of the leaf blade. Both extremes, as well as intermediates, are well-represented in Missouri herbaria. Examination of a large number of specimens suggests that the different leaf-shapes do not correlate well with the varieties historically recognized primarily on fruit characteristics. Crataegus hispidula, C. insperata, C. obscura, and C. spinulosa represent the broader-leaved, more sharply lobed forms, and C. calpodendron var. calpodendron, var. globosa, and var. mollicula, as well as C. mollita include the more elliptic-leaved forms. Crataegus scabera and C. spinulosa are intermediates. In practice, there is far too much variability among the Missouri plants to allow the formal recognition of any infraspecific taxa.

Crataegus rupicola Sarg. (C. harveyana Sarg.) represents a rare form with a few glands at the base of the leaf and on the petiole, which is an indication that it is perhaps of hybrid origin, involving a cross between C. calpodendron and a species in some other series (such glands occur most frequently in ser. Intricatae, but are produced by some taxa in a few other series as well).