2. Aesculus L. (buckeye)

Plants shrubs or trees, lacking tendrils. Bark variously light to dark-colored, smooth to scaly. Twigs gray to reddish brown, with light yellowish lenticels and relatively large leaf scars, the winter buds ovoid to more or less conical, sharply pointed (blunt in A. pavia), with several pairs of overlapping scales, these often somewhat keeled, rounded at the tip and often with a minute sharp point. Leaves opposite, long-petiolate. Stipules lacking, but small tufts of purplish cobwebby hairs or minute dark scales often present at the leaflet bases. Leaf blades palmately compound, pentagonal to kidney-shaped or nearly circular in overall outline, with 5–11 leaflets, these often short-stalked, oblanceolate to obovate or elliptic, angled or tapered at the base, angled or more commonly tapered to a sharply pointed tip, the margins finely and sharply toothed. Inflorescences terminal on the branches, cylindrical to ovoid panicles, the main axis usually densely pubescent with short, curly hairs, sometimes also with tufts of longer, cobwebby, reddish purple hairs at the branch points, the flowers relatively densely racemose along the pinnate main branches. Flowers zygomorphic, hypogynous. Calyces 5-lobed, usually not green, variously shaped but usually only slightly zygomorphic, with relatively shallow, rounded to bluntly pointed lobes, the outer surface densely pubescent with minute, curved or curled hairs, often also with sparse to moderate, gland-tipped hairs, usually not persistent at fruiting. Corollas of 4 free petals (5 elsewhere), the lowermost petal usually abortive, slightly to relatively strongly zygomorphic, the upper pair usually somewhat longer and narrower than the lower pair, all tapered to flattened or winged, stalklike bases, variously colored, the margins and outer surface variously hairy. Stamens 6–8 (except in pistillate flowers), the anthers yellow, orange, or red. Pistil of (2)3 fused carpels (except in staminate flowers), usually 3-locular. Style 1, elongate, unbranched, the stigma entire or only slightly lobed. Fruits capsules, dehiscent longitudinally, the surface sometimes with spinelike tubercles, 1–3-seeded. Seeds 2–4 cm long, variously depressed-globose, often with a somewhat flattened area, the surface often faintly wrinkled, smooth, tan to dark reddish brown with a large, pale, attachment scar.

The horse chestnut, which is native to Europe and Asia, is widely cultivated in temperate North America as an ornamental shade tree and for its seeds, which are roasted and eaten. It may be recognized by its large (often 10–25 cm long) leaflets, 5-petaled flowers (the lower petal well-developed), and very large (often more than 5 cm in diameter), spiny fruits. It has escaped from cultivation only rarely in North America has not escaped thus far in Missouri (Steyermark, 1963).

The two species native to Missouri also have been roasted for food, but they have smaller seeds sometimes with inferior flavor. It should be noted that raw seeds (or other portions of the plant) are considered mildly toxic to livestock and humans, containing a complex array of chemical compounds that can cause symptoms of intoxication, including an unbalanced stance, staggering or exaggerated movements, and rarely muscle spasms and collapse (Burrows and Tyrl, 2001). The crushed seeds have been scattered into ponds as a poison to stun fish (Steyermark, 1963).

Buckeyes are of only minor value for their lightweight, relatively brittle timber, which occasionally has been used in furniture, musical instruments, or implements. The roots occasionally were used by pioneers to produce a soap. The large seeds of buckeyes have been carried in the pocket for their pleasant, smooth texture, as a good luck charm, and as a folk remedy for rheumatism. The principal use of both of the Missouri species is for cultivation as ornamentals.

Buckeyes produce new foliage relatively early in the spring and are among the earliest woody species to drop their leaves in the autumn. The seeds tend to germinate very quickly after dispersal, but enter a deep physiological dormancy that is very difficult to break if allowed to dry (Baskin and Baskin, 1998). Thus, they cannot be stored for future germination using standard seed storage protocols.