Decaisnea insignis Seeds | Blue Sausage Fruit
LATIN NAME: Decaisnea insignis
COMMON NAME: Blue Sausage Fruit
Plant Profile
Decaisnea insignis is best known for its fruit: a long, cylindrical blue-violet fruit, fleshy, that hangs in a cluster and looks, frankly, like a fat sausage. It is one of the few blue fleshy fruits in temperate horticulture, which makes the plant a curiosity wherever it is grown. The fruit is a follicle — a dry fruit type in most plants, but here swollen and fleshy — and that odd combination is the species’ calling card.
The plant is a deciduous shrub or small tree with large, pinnate leaves of many oval leaflets, giving a bold, tropical look in a temperate garden. In early summer it bears drooping panicles of small, greenish-yellow flowers shaped like bells. Male and female flowers sit on the same plant, and only the fertilised female flowers swell into the blue follicles. The bold leaf and the odd fruit together make a striking specimen.
The species spans the moist woodlands of the Himalaya and the mountains of west China, from roughly 1500 to 3000 metres, where summers are cool and the air humid. It wants the same cool, leafy ground that is well drained in cultivation and resents hot, dry plains. That montane taste explains why it thrives in maritime and highland gardens but struggles in continental heat.
Left alone the plant makes a loose, scrambling shrub; train it against a wall or through a sturdy frame to show the fruit to best effect. Prune only to shape and to open the centre after fruiting. Feed with a balanced feed in spring, water in dry spells, and protect young wood from late frost. The chief troubles are slug damage to low leaves and crown rot in wet ground; both yield to good drainage and air flow.
Science & Biotechnology
The pulp and seed carry saponin-like compounds, which is why the flesh is slimy and mildly soapy to the touch — a trait shared with other Lardizabalaceae. The saponins are a research interest rather than a use, and they are the likely reason the raw seed is unpalatable. Study of the genus has mapped these glycosides alongside the fruit’s sugars and acids.
Uses & Benefits
Inside the blue skin is a translucent, sweet pulp with a mild flavour that surrounds a row of flat, dark seeds that are hard. The pulp is edible and pleasant, rather like a mild custard apple in texture, but the seeds are not — they are bitter and should be spat out. This split between edible aril-like pulp and inedible seed is the practical rule for anyone who tries the fruit: scrape the pulp, discard the seeds. The seeds themselves are the propagation unit. Birds largely ignore the fruit, perhaps because the pulp, while sweet, is thin and the seeds are bitter, so the plant spreads mostly by its own dropped fruit rolling to a neighbour rather than by being carried far.
Growing from Seed
The flat seeds are rich in storage lipids — glyceride fats that the embryo draws on as it grows. Work on related Lardizabalaceae seeds has examined the fatty-acid profile, which is of interest to oil chemists. For the grower the point is that the seed is oily and thus shorter-lived than a dry legume seed: sow it fresh and do not let it dry out for long. Some growers nick the flat edge lightly before the cold treatment to speed the coat split, though the seed will usually open on its own given a full cool, moist period and a warm follow-on.
Sow the fresh, cleaned seed in a deep pot of leafy, gritty loam, covering with twice its depth of medium. A cool, moist rest helps the hard coat split, so a spring sowing after a cool spell suits it. Space the pots so the seedlings are not shaded, keep the medium evenly moist, and top with grit to stop crusting. Mark the pots, as the seed is slow.
The flat seed benefits from a period of cold, moist treatment to soften the coat, after which a warm bench brings steady emergence. Sow deeper than a fine seed — about twice the seed’s thickness — so the radical can anchor. Thin to one seedling per pot when the first true leaf opens, and avoid letting the surface swing wet to dry.
Move seedlings to individual pots when the first true leaf is fully open. Handle by the leaf, keep the root straight in the deep pot, and set at the same depth. Grow on in light shade for the first season so the bold leaves harden without scorch.
Our Take
For related odd-fruited vines, the chocolate vine at Akebia trifoliata, the five-leaf akebia at Akebia quinata, and the stauntonia at Stauntonia latifolia belong to the same montane clan and fruit in a similar cool, leafy way.
Related Reading
More species in the same orbit as Blue Sausage Fruit: