Sterculia subracemosa Seeds | Sterculia
LATIN NAME: Sterculia subracemosa
COMMON NAME: Sterculia
Plant Profile
Leaves are simple and alternate on a petiole 1.5 to 2.5 centimetres long, and both stalk and blade carry minute black glands that show up best on dried material. The blade is oblanceolate to elliptic-obovate, eleven to eighteen centimetres long, hairless on both faces, with eight to ten pairs of lateral veins that rejoin in a looping network inside the margin instead of running straight out to it. That vein detail is what separates the species from its closest relatives.
No Sterculia carries petals, so the whole display is the calyx: a bell-shaped tube about thirteen millimetres long opening into five lobes slightly longer than the tube. Recorded colour runs from white tinged with pink to orange-red. Female flowers carry about seventeen staminodes around a globose ovary of some 1.5 millimetres with a five-lobed stigma, and flowering falls in March and April.
The 1947 paper places the new shrub beside Sterculia lanceaefolia, a more widespread plant with narrower leaves and darker flowers, and notes that it approaches Sterculia hainanensis of Hainan. The distinguishing features are the obovate-oblong leaf and the pale calyx, and in a genus of similar shrubs those are the characters that settle an identification.
Older references file this plant under Sterculiaceae, a family since dismantled into an expanded Malvaceae. Sterculia now sits in the subfamily Sterculioideae, while two former companions, cacao and the kola nut, went to Byttnerioideae. The reshuffle explains why a petal-less shrub is treated as a relative of hibiscus and cotton.
The group shares a plan: flowers without petals, a stalked column carrying the stamens, mucilage in the tissues, and seeds that store unusual fatty acids. The genus name itself comes from the Latin word for dung, after the foetid flowers of its better-known members.
Sterculias are grown indoors as foliage and curiosity plants far more often than as crop plants, and the routine is uniform: warmth, humidity, a free-draining mix, and no cold nights at all.
Science & Biotechnology
Where Sterculia seed oil has been examined it has proved chemically unusual. The genus is a source of cyclopropenoid fatty acids, sterculic acid chief among them, whose three-membered ring is rare in plant oils and makes the fat behave quite unlike an ordinary culinary oil. Almost all of that work rests on better-documented species; this seed has never been analysed, because it has never been found.
Sterculic acid, with its shorter relative malvalic acid, is studied as an inhibitor of the desaturase that converts saturated fatty acids into monounsaturated ones. That property made the compounds laboratory tools in lipid research and kept Sterculia seed oils out of the food chain. The cyclopropene ring, not the chain length, does the work.
Uses & Benefits
The genus Sterculia is full of large tropical trees with fluted trunks, so the first surprise here is scale. Sterculia subracemosa is a shrub of roughly three and a half metres, its slender branchlets drying a distinctive red-brown beneath a sparse coat of star-shaped hairs. Nothing in its frame suggests canopy timber; it belongs to the understorey of warm hill forest, in gullies and on slopes between about five hundred and six hundred metres.
Chun Woon-Young and Hsue Hsiang-Hao published the species in the Journal of the Arnold Arboretum in 1947, from material gathered beside a stream at Xinyi on 21 March 1932. The specimen carried flowers and no fruit, and later accounts repeat the admission. For a genus whose trade is built on seed, that is a remarkable position for a species to occupy.
Growing from Seed
For a species with no recorded fruit, vegetative propagation is not a convenience but the only dependable route. The wider genus has been taken into sterile culture from shoot tips and nodal segments, with a cytokinin to break bud dormancy and an auxin to induce rooting, and Sterculia foetida is among the best documented. Rooting leafy cuttings is far simpler than raising seedlings from a fruit nobody has described.
Build the mix from two parts loam-based compost to one part coarse grit, with a handful of leaf mould worked through, and use a pot deep enough for the taproot these plants run early. Where seed of any sterculia comes to hand, sow it barely covered, because large soft seeds rot under a heavy layer, and hold the pot warm in bright, filtered light.
Water when the top centimetre of mix dries and never leave the pot in a saucer, because the fleshy roots resent it. Feed lightly through the growing season and give light shade at midday, which suits a shrub that evolved under a forest canopy. Hold the plant above about ten degrees in winter, since one cold night undoes a season of growth. Scale insects and mealybug are the usual indoor pests; a monthly look under the leaves beats any spray applied later.
Our Take
Sterculia subracemosa is a plant to grow for interest rather than yield: a small Chinese shrub with pale calyces and a fruit no herbarium holds. On the same warm bench, our notes on the stinking sterculia cover the genus’s tougher ornamental member, while Sterculia monosperma is the relative that does yield a harvestable seed. For the family’s most famous crop, read the file on cacao.
Related Reading
More species in the same orbit as Sterculia: