Flower:

Flat-topped, branching cluster of 5 to 12 flowers at tips of branch twigs, emerging after the leaves in mid to late spring. Flowers are ½ to 2/3 inch across with 5 round white petals. In the center are usually 5 to 10 stamens, though there may be as many as 20; stamen tips (anthers) are usually pale to deep pink, occasionally white.

The 5 sepals around the base of the flower are narrowly triangular to awl shaped, smooth along the edges or with a few glands dotting the edge or at the tips of minute, shallow teeth. Sepals and the cup-shaped hypanthium below the sepals are both hairless; flower stalks are hairless to sparsely hairy.

Leaves and stems:

Leaves are alternate, 1 to 2½ inches long, up to 2 inches wide, egg-shaped, mostly widest near the base, mostly pointed at the tip, mostly rounded at the base but may be somewhat wedge-shaped to somewhat heart-shaped. Edges are toothed nearly to the base with dark red glands at the tips of most teeth, and usually have 3 to 5 small but distinct lobes per side. The upper surface is variously covered in stiff, appressed hairs, the lower completely hairless. The stalk is slender, about half (or more) as long as the blade, hairless or with a few hairs on the upper surface and has a few to several red glands on the edges.

Young twigs are hairless, yellowish to reddish brown, turning gray the 3rd year and developing straight to slightly curved thorns 1 to 2½ inches long. Thorns are usually abundant and are shiny dark brown to blackish or black-tipped when young.

Mature bark is thin, gray to gray-brown and splits into narrow plates. Stems are multiple from the base and may reach 5 inches in diameter on larger stems. Compound thorns are absent, branches are erect to ascending. Plants are not colony-forming or root-suckering.

Fruit:

Fruit is fleshy and berry-like, oblong to oval to nearly round, about ½ inch diameter, dull, bright to deep red at maturity.

Notes:

Large-seeded Hawthorn, also known as Eastern Hawthorn, reaches the northwest tip of its range in Minnesota, found in a variety of habitats and soil conditions. While it is documented as reaching heights of 23 feet, in Minnesota it typically tops out at around 10 feet.

Large-seeded Hawthorn is recognized by the combination of: multi-stemmed shrub (occasionally tree-like) lacking compound thorns; erect to ascending branches with abundant straight to slightly curved thorns 1 to 2½ inches long; leaves hairless on the underside, few if any hairs on the slender leaf stalks but usually at least a few glands; flowers usually with 5 to 10 stamens and pink anthers, but may have up to 20 stamens or white anthers; sepals and hypanthium hairless, flower stalks hairless to sparsely hairy, sepals with or without glands along the edge. Fruit is almost rectangular in outline to oval to nearly round, dull, bright to deep red at maturity. The leaves are relatively small and thin compared to other Hawthorns.

According to Welby Smith's book “Trees and Shrubs of Minnesota”, Minnesota populations show a lot more variation than in the east, where flower stalks are described as hairless, sepals lack any glands, and flowers are not noted as having more than 10 stamens. Crataegus macrosperma is most likely to be confused with C. chrysocarpa (Fireberry Hawthorn), which has leaves of a similar shape and size that are also sometimes hairless on the underside, stamens also may number 5 to 20 and anthers may be white or pink, but its leaves tend to be more consistently wedge-shaped (i.e. a straight angle, not curved) at the base, flower stalks tend to be more consistently and densely hairy, sepals more consistently glandular and/or toothed along the edge, and the hypanthium is always hairy, at least for the varieties known to be in Minnesota.