Aesculus parviflora Seeds | Bottlebrush Buckeye
LATIN NAME: Aesculus parviflora
COMMON NAME: Bottlebrush Buckeye
Plant Profile
When Thomas Walter published the Flora Caroliniana in 1788 he set the name on the first North American buckeye to be described by a botanist, and the plant he knew is still one of the oddities of the genus. The horse chestnut of European parks and the red buckeyes of the American woods both flower on the bare or half-open tree in spring. Bottlebrush buckeye flowers in the middle of summer, on a wide suckering shrub that spreads underground, and it does so with flower spikes that rise well clear of the foliage. Nothing else in the genus behaves quite like it.
The flower spike is the giveaway. The European horse chestnut and most of its relatives hide short stamens inside a bowl of clawed petals; this species narrows the petals into a slender tube and pushes six or seven long stamens well beyond the mouth, so the whole spike reads as a bottlebrush rather than a candelabra of cups. The flowers are white, faintly tinted with pink at the base, and they open in sequence from the bottom of the spike upward, which keeps a colony in bloom for a long stretch of high summer. Bees and butterflies work the spikes continuously while they last.
Each leaf is a fan of five, sometimes seven, obovate leaflets up to about twenty centimetres long, borne on a long stalk. The leaflets are held in a flat hand, glossy above and softly haired beneath, and they turn a soft even yellow in autumn. The shrub is only two to three metres tall, but it spreads sideways by stolons, so a single planting becomes a colony several metres across that marches slowly through a border.
The spikes are borne upright on the current season’s growth, reaching a good thirty centimetres on a well-grown clump, at the point in the year when most flowering shrubs have finished.
Science & Biotechnology
The genus is rich in the coumarin glucoside aesculin, which hydrolyses to the aglycone aesculetin. Those two compounds left a mark far outside botany: aesculin is the reagent in the bile-esculin agar test used to tell enterococci from other streptococci, because organisms that split the glucoside release aesculetin, which reacts with ferric citrate in the medium and turns the colony black. Every hospital laboratory that identifies a urinary enterococcus is using a buckeye compound to do it.
The seeds carry triterpenoid saponins of the escin type along with aesculin, and they are bitter and toxic enough that no one cooks with them. The same saponin chemistry has been studied for years in the European horse chestnut as a treatment for heavy, swollen legs, and the traditional use of buckeye nuts as a fish stupefying agent in North America rests on the same detergency: the saponins froth in water and interfere with the gills.
Aesculus has a textbook distribution. Species grow in eastern Asia, in eastern North America and in Europe, with a single outlier in California, and chromosome counts run at forty across the genus. Molecular work on the group has used that pattern to argue about how the horse chestnuts crossed between continents, and the shrubby, tubular-flowered species of the southeastern United States take a place near the base of the family tree. Embryo rescue is also used in the genus to raise hybrids that would otherwise abort.
Uses & Benefits
This is a plant for the woodland edge, the north wall and the awkward gap under a mature tree, where its tolerance of root competition makes it valuable. Plant it in groups of three to build a colony, or single it in a large bed and let it spread. The flowers are a genuine mid-summer nectar source at a lean point in the season for bees. Because the foliage and seed are poisonous, it is not a plant for a paddock or a garden where children graze.
Growing from Seed
Buckeye seed is recalcitrant: it has no ability to survive drying, and a nut left on a shelf loses its power to grow within a short time. Sow it as soon as it falls, five centimetres deep, on its side, in a deep pot, using two parts loam, one part leafmould and one part coarse grit. The seed leaves stay in the soil while the shoot lifts, and the first root runs straight down, so a deep container matters more than a wide one. Move each seedling on once the first pair of true leaves has opened.
To make a new clump, lift a rooted sucker in early spring with a spade and cut it clean from the parent. To hold an old colony in bounds, cut the outermost stems at ground level after flowering. The plant wants deep, humus-rich ground that does not dry out completely, and it scorches in a hot, windy position. An annual mulch is the whole of its feeding, and no winter protection is needed in a cold garden.
A leaf blotch fungus can speck the foliage in a wet summer, and the genus’s leaf-mining moth, notorious on horse chestnuts, is far less damaging here because the foliage emerges late. Rake up fallen leaves under the colony to reduce both, and water the clump in a drought year so that the leaves do not brown early.
Our Take
For a dark corner that defeats most flowering shrubs, few things beat a colony of bottlebrush buckeye in July. If you want the spring-flowering end of the genus, the red buckeye is a smaller native shrub with scarlet spikes, and the Indian horse chestnut suits a bigger, wetter site. The horse chestnut and buckeye group as a whole is worth growing for the foliage alone.
Related Reading
More species in the same orbit as Bottlebrush Buckeye: