Kalopanax septemlobus Seeds | Castor Aralia
LATIN NAME: Kalopanax septemlobus
COMMON NAME: Castor Aralia
Plant Profile
Put a hand on the trunk of a young castor aralia and you will not do it twice. The bark of Kalopanax septemlobus carries rows of stout conical prickles that grow out of the corky outer tissue, and a sapling is armoured from ankle to crown. Above that spiny stem it holds leaves of a size that seems out of keeping with a temperate tree, divided into seven pointed lobes on a long stalk.
The aralia family is best known for ginseng and its relatives, and it has a consistent architecture: small five-parted flowers crowded into umbels, and a fleshy fruit containing a pair of pyrenes. Castor aralia follows that plan at tree scale, which is unusual in a family otherwise of shrubs and herbs. The prickles are outgrowths of the outer stem layers, not leaf spines.
The flowers open in late summer in a broad flat-topped cluster made of many small umbels, greenish-white and only a few millimetres across, and the whole head is worked by bees, flies and beetles over several weeks. The fruit that follows is a blue-black drupe, taken by birds in autumn and carried away from the parent tree.
The species ranges through the cool moist forests of China, Korea, Japan and the southern Russian Far East, on deep leaf litter in mixed stands and along forest edges. Young plants in shade hold enormous, deeply divided leaves and many seedlings live for years in the understorey looking more like a herbaceous perennial than a tree. As they reach the canopy the leaves change.
Castor aralia wants cool summers, wet air and humus, and it indicates a fertile forest floor. A mature flowering tree carries smaller leaves with fewer lobes and fewer prickles than its own seedling, so the two look like different species in the same wood. In parts of its range it has become uncommon as old forest is cleared.
Science & Biotechnology
The stem bark is loaded with triterpenoid saponins of the hederagenin and oleanolic acid type, recorded in the literature as a series of kalopanaxsaponins, alongside lignans and phenolic glycosides. Saponins of this kind foam in water, which is why a decoction of the bark lathers, and they carry the bitter acrid character a medicinal bark needs. The wood was worked for small durable goods.
Among the compounds isolated from the genus, the lignan liriodendrin has been studied for anti-inflammatory and analgesic activity in laboratory models, which fits the traditional use of the bark against rheumatic pain. Work of this kind is chemical rather than clinical, but it explains why the species appears in the pharmacology literature as well as the horticultural one.
Uses & Benefits
In spring, before the prickles harden, the young shoots are gathered in Korea and Japan as a seasonal vegetable: boiled, then dressed, or cooked into a savoury dish, the bitterness reduced by parboiling. It is a wild-harvest crop rather than a market one, taken from cut stools and root suckers, and cutting forces more shoots the following year.
Because the flower heads are broad, open and produced in late summer when much of the forest has finished, the tree is valued by beekeepers in its native range as a source of late nectar and pollen. Hives sited near stands work the umbels heavily, and the honey is darker and more strongly flavoured than spring honey from the same district.
Growing from Seed
With natural stands declining and the species slow from seed, tissue culture has been developed as a practical route to planting stock. Somatic embryogenesis from immature seed tissue and shoot multiplication from nodal explants have both been reported for Kalopanax, each followed by rooting and a shaded acclimatisation stage, which allows selected genotypes to be bulked quickly and evenly.
The seed of the aralia family is generally shed with an immature embryo, and this species is no exception: it needs a moist warm spell to finish developing before it will respond to winter cold. Clean the flesh off the drupes, mix the seed with damp sand in a covered pan and keep it warm and shaded for the rest of the season, then move the pan to a cold frame for the winter. Sow in early spring, covering the seed with about a centimetre of mix, and thin the seedlings once the second true leaf has opened so the plants stand several centimetres apart. Do not be alarmed when the leaves grow larger and more divided each year.
Our Take
Castor aralia is a plant for the patient grower with a big garden, and its rewards are a thicket of enormous leaves and late-summer nectar rather than quick ornament. If you like the family, our pages on the Japanese angelica tree and on Trevesia palmata cover two araliads of comparable scale, and Fatsia gives the same leaf quality at shrub size.
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